Gerard Heck - Profile on Academia.edu (original) (raw)
Papers by Gerard Heck
Involvement of NADPH-Dependent and cAMP-PKA Sensitive H+ Channels in the Chorda Tympani Nerve Responses to Strong Acids
Chemical Senses, Feb 21, 2011
Dietary Na(+)-restriction prevents development of functional Na+ channels in taste cell apical membranes: proof by in vivo membrane voltage perturbation
Journal of Neurophysiology, Oct 1, 1993
1. Chorda tympani (CT) neural responses to NaCl were recorded while the potential across the apic... more 1. Chorda tympani (CT) neural responses to NaCl were recorded while the potential across the apical membrane of taste cells was perturbed by voltage clamp in rats fed a Na(+)-restricted diet pre- and postnatally (Na(+)-restricted rats) and in controls. 2. Control rats gave CT responses that were enhanced at negative voltage clamp and suppressed at positive voltage clamp. In contrast, CT responses from Na(+)-restricted rats were virtually voltage insensitive. 3. Analysis of the voltage-sensitivity of the CT response shows that Na(+)-restricted rats have < 10% of the density of functional apical Na+ channels normally present in control rats demonstrating that early dietary Na(+)-restriction prevents the functional expression of these key elements in salt taste transduction. Furthermore, the data demonstrate the value of this technique in assessing involvement of distinct cellular domains in taste transduction.
Surface active taste modifiers: a comparison of the physical and psychophysical properties of gymnemic acid and sodium lauryl sulfate
Chemical Senses, 1980
Abstract We have compared the surface active properties of gymnemic acid with those of the wellkn... more Abstract We have compared the surface active properties of gymnemic acid with those of the wellknown surfactant sodium lauryl sulfate. Aqueous solutions of gymnemic acid produce a surface tension-concentration relation similar to that of water soluble surfactants. Its form ...
The Journal of General Physiology, May 1, 1984
The electrophysiological properties of the dorsal and ventral canine lingual epithelium are studi... more The electrophysiological properties of the dorsal and ventral canine lingual epithelium are studied in vitro. The dorsal epithelium contains a special ion transport system activated by mucosal solutions hyperosmotic in NaCl or LiCl. Hyperosmotic KCl is significantly less effective as an activator of this system. The lingual frenulum does not contain the transport system. In the dorsal surface it is characterized by a rapid increase in inward current and can be quantitated as a second component in the time course of either the opencircuit potential or short-circuit current when the mucosal solution is hyperosmotic in NaCl or LiCl. The increased inward current (hyperosmotic response) can be eliminated by amiloride (10' M). The specific location of this transport system in the dorsal surface and the fact that it operates over the concentration range characteristic of mammalian salt taste suggests a possible link to gustatory transduction. This possibility is tested by recording neural responses in the rat to NaCl and KCl over a concentration range including the hyperosmotic. We demonstrate that amiloride specifically blocks the response to NaCl over the hyperosmotic range while affecting the KCl response significantly less. The results suggest that gustatory transduction for NaCl is mediated by Na entry into the taste cells via the same amiloride-sensitive pathway responsible for the hyperosmotic response in vitro. Further studies of the in vitro system give evidence for paracellular as well as transcellular current paths. The transmural current-voltage relations are linear under both symmetrical and asymmetrical conditions. After ouabain treatment under symmetrical conditions, the shortcircuit current decays to zero. The increase in resistance, though significant, is small, which suggests a sizeable shunt pathway for current. Flux measurements show that sodium is absorbed under symmetrical conditions. Mucosal solutions hyperosmotic in various sugars also induce an amiloride-sensitive inward current. In summary, this work provides evidence that the sodium taste receptor is most probably a sodium transport system, specifically adapted to the dorsal surface of the tongue. The transport paradigm of gustation also suggests a simple model for electric taste and possible mechanisms for sweet taste .
Evidence for electrogenic active ion transport across the frog olfactory mucosa in vitro
Chemical Senses, 1984
ABSTRACT
PLOS ONE, May 19, 2014
The effects of small molecule ENaC activators N,N,N-trimethyl-2-((4-methyl-2-((4-methyl-1H-indol-... more The effects of small molecule ENaC activators N,N,N-trimethyl-2-((4-methyl-2-((4-methyl-1H-indol-3-yl)thio)pentanoyl)oxy)ethanaminium iodide (Compound 1) and N-(2-hydroxyethyl)-4-methyl-2-((4-methyl-1H-indol-3-yl)thio)pentanamide (Compound 2), were tested on the benzamil (Bz)-sensitive NaCl chorda tympani (CT) taste nerve response under opencircuit conditions and under 660 mV applied lingual voltage-clamp, and compared with the effects of known physiological activators (8-CPT-cAMP, BAPTA-AM, and alkaline pH), and an inhibitor (ionomycin+Ca 2+) of ENaC. The NaCl CT response was enhanced at 260 mV and suppressed at +60 mV. In every case the CT response (r) versus voltage (V) curve was linear. All ENaC activators increased the open-circuit response (r o) and the voltage sensitivity (k, negative of the slope of the r versus V curve) and ionomycin+Ca 2+ decreased r o and k to zero. Compound 1 and Compound 2 expressed a sigmoidal-saturating function of concentration (0.25-1 mM) with a half-maximal response concentration (k) of 0.49 and 1.05 mM, respectively. Following treatment with 1 mM Compound 1, 8-CPT-cAMP, BAPTA-AM and pH 10.3, the Bz-sensitive NaCl CT response to 100 mM NaCl was enhanced and was equivalent to the Bz-sensitive CT response to 300 mM NaCl. Plots of k versus r o in the absence and presence of the activators or the inhibitor were linear, suggesting that changes in the affinity of Na + for ENaC under different conditions are fully compensated by changes in the apical membrane potential difference, and that the observed changes in the Bz-sensitive NaCl CT response arise exclusively from changes in the maximum CT response (r m). The results further suggest that the agonists enhance and ionomycin+Ca 2+ decreases ENaC function by increasing or decreasing the rate of release of Na + from its ENaC binding site to the receptor cell cytosol, respectively. Irrespective of agonist type, the Bz-sensitive NaCl CT response demonstrated a maximum response enhancement limit of about 75% over control value.
Journal of Neurophysiology, Mar 1, 1997
psychophysical studies have suggested simi-Chorda tympani responses under lingual voltage clamp: ... more psychophysical studies have suggested simi-Chorda tympani responses under lingual voltage clamp: implicalarities in the taste quality profiles of NH 4 Cl and KCl. In tions for NH 4 salt taste transduction. J. Neurophysiol. 77: 1393addition, functional similarities at the level of nucleus tractus 1406, 1997. Rat chorda tympani (CT) responses to NH 4 Cl, ammosolitarius for NH / 4 and K / salts have been suggested (Nakanium acetate (NH 4 Ac), and ammonium hippurate (NH 4 Hp) were mura and Norgren 1993). NH / 4 and K / ions have similar obtained during simultaneous current and voltage clamping of the hydrated radii and ionic conductances in free solution (Kneplingual field potential. Although functional and developmental simper et al. 1989). These ions may also have similar properties ilarities for gustation have been reported for NH / 4 and K / salts, at the cell membrane level, e.g., NH / 4 has been found to we report here that significant differences are discernible in the CT responses to both salts. Unlike neural responses to KCl, those substitute for K / on transporters in many cell types (Amlal to NH 4 Cl are voltage sensitive, enhanced by submucosa negative et al. 1994; Kinne et al. 1986; Tsuruoka et al. 1993). and suppressed by positive voltage clamp. In this regard, NH 4 Cl Developmental studies of salt taste in neonatal rats responses are qualitatively similar to NaCl responses; however, the show that CT responses to NH 4 Cl are fully developed magnitude of NH 4 Cl voltage sensitivity is significantly less than before those to NaCl (Hill et al. 1982; Mistretta and that of NaCl. The concentration dependence of the CT response Bradley 1980; Yamada 1980). Recordings from more to NH 4 Cl manifests a biphasic nonlinear relationship not observed central loci in the taste neuraxis, in the nucleus tractus with KCl or NaCl. Below 0.3 M, the CT response increases as if to solitarius (Hill et al. 1983) , and in cortical taste areas approach a saturation value. However, beyond 0.3 M an inflection (Ogawa et al. 1994) are generally consistent with this. appears in the CT-concentration curve because of an abrupt increase in CT responses. This kinetic profile is Cl 0 dependent and The different maturation rates for NaCl and NH 4 Cl neural is correlated with an increase in transepithelial conductance that responses suggest that taste receptors for NH / 4 and Na / displays similar NH 4 Cl concentration dependence. The biphasic are, at least in part, functionally distinct. A recent study relation to salt concentration is not observed when acetate or hipindicates that K / salt CT responses are mediated by a purate is substituted for Cl 0. As with Na / and K / salts, less single, diffusion-controlled voltage-insensitive transducmobile anions than Cl 0 (Ac 0 and Hp 0) lower the CT responses. tion mechanism (Ye et al. 1994). K / salt taste responses However, like Na / salts, but in contrast to K / salts, the onset occur via a sub-tight junctional transducer for K / ions kinetics of CT responses to NH 4 Ac or NH 4 Hp remain rapid, even with access limited by anion mobility. In contrast, NaCl under positive voltage-clamp conditions. Amiloride (100 mM) partially suppresses CT responses within the concentration range of CT responses consist of a voltage-dependent (amiloride-0.05-0.3 M (48-20% suppression). Amiloride also suppresses sensitive) component and smaller voltage-independent the voltage sensitivity of NH 4 Cl CT responses, but does not elimi-(amiloride-insensitive) component (Ye et al. 1993). The nate that sensitivity as it does for Na / salts. In conclusion, the data amiloride and voltage sensitivity suggests that this Na suggest that taste transduction for NH 4 salts is mediated over two taste transducing element is an apical membrane ion NH / 4 conduction pathways in the taste bud. This is especially evichannel (Avenet and Lindemann 1991; Garty and Benos dent with NH 4 Cl, where the CT-concentration curves show two 1988). The amiloride-insensitive component depends on distinct kinetic regimes. Below 0.3 M the saturation with increasing the presence of Cl 0 in Na salt taste (Elliott and Simon concentration, clamp voltage response dependence, and amiloride 1990; Formaker and Hill 1988; Ye et al. 1993). sensitivity suggest an apical membrane transduction conductance. Above 0.3 M, the high anion dependence of the response and The main objective of this study is to investigate the transits amiloride insensitivity indicate participation of the paracellular duction mechanisms involved in NH / 4 salt taste perception. pathway in transduction. This was accomplished by comparing CT responses to NH / 4 salts, with the use of the in situ lingual voltage-clamp method, with the responses to Na / and K / salts. The results I N T R O D U C T I O N indicate the presence of two transduction mechanisms for NH 4 Cl: an apical NH / 4 ion conductance, dominant with NH 4 Cl has been widely used as a reference stimulus in NH 4 Cl concentrations below Ç0.3 M, and a mechanism acrecordings from different levels of the taste sensory system cessible via the paracellular pathway. The latter is especially in various animal models. These include cortical taste areas prominant in the presence of Cl 0 and with NH / 4 concentra-(Ogawa et al. 1994), the nucleus tractus solitarius (Hill et al. tions ú0.3 M. 1983; Nakamura and Norgren 1993), and the chorda tympani
Journal of Neurophysiology, Sep 1, 2007
The effect of nicotine on the benzamil (Bz)-insensitive (transient receptor potential vanilloid-1... more The effect of nicotine on the benzamil (Bz)-insensitive (transient receptor potential vanilloid-1 variant cation channel, TRPV1t) and the Bzsensitive (epithelial Na ϩ channel, ENaC) salt taste receptors and sour taste was investigated by monitoring intracellular Na ϩ and H ϩ activity (pH i) in polarized fungiform taste receptor cells (TRCs) and the chorda tympani (CT) nerve responses to NaCl, KCl, and HCl. CT responses in Sprague-Dawley rats and both wildtype and TRPV1 knockout (KO) mice were recorded in the presence and absence of agonists [resiniferatoxin (RTX) and elevated temperature] and an antagonist (SB-366791) of TRPV1t, the ENaC blocker (Bz), and varying apical pH (pH o). At concentrations Ͻ0.015 M, nicotine enhanced and at Ͼ0.015 M, it inhibited CT responses to KCl and NaCl. Nicotine produced maximum enhancement in the Bz-insensitive NaCl CT response at pH o between 6 and 7. RTX and elevated temperature increased the sensitivity of the CT response to nicotine in salt-containing media, and SB-366791 inhibited these effects. TRPV1 KO mice demonstrated no Bz-insensitive CT response to NaCl and no sensitivity to nicotine, RTX, and elevated temperature. We conclude that nicotine modulates salt responses by direct interaction with TRPV1t. At pH o Ͼ8, the apical membrane permeability of nicotine was increased significantly, resulting in increase in TRC pH i and volume, activation of ENaC, and enhancement of the Bz-sensitive NaCl CT response. At pH o Ͼ8, nicotine also inhibited the phasic component of the HCl CT response. We conclude that the effects of nicotine on ENaC and the phasic HCl CT response arise from increases in TRC pH i and volume.
The Journal of Physiology, Mar 30, 2004
The role of basolateral Na+–H+ exchanger isoform-1 (NHE-1) was investigated in neural adaptation ... more The role of basolateral Na+–H+ exchanger isoform-1 (NHE-1) was investigated in neural adaptation of rat taste responses to acidic stimuli, by direct measurement of intracellular pH (pHi) in polarized taste receptor cells (TRCs) and by chorda tympani (CT) taste nerve recordings. In TRCs perfused with CO2/HCO3−-free solution (pH 7.4), removal of basolateral Na+ decreased pHi reversibly and zoniporide, a specific NHE-1 blocker, inhibited the Na+-induced changes in pHi. The spontaneous rate of TRC pHi recovery from NH4Cl pulses was inhibited by basolateral zoniporide with a Ki of 0.33μm. Exposure to basolateral ionomycin, reversibly increased TRC Ca2+, resting pHi, and the spontaneous rate of pHi recovery from an NH4Cl pulse. These effects of Ca2+ on pHi were blocked by zoniporide. In in vivo experiments, topical lingual application of zoniporide increased the magnitude of the CT responses to acetic acid and CO2, but not to HCl. Topical lingual application of ionomycin did not affect the phasic part of the CT responses to acidic stimuli, but decreased the tonic part by 50% of control over a period of about 1 min. This increased adaptation in the CT response was inhibited by zoniporide. Topical lingual application of 8-CPT-cAMP increased the CT responses to HCl, but not to CO2, and acetic acid. In the presence of cAMP, ionomycin increased sensory adaptation to HCl, CO2, and acetic acid. Thus, cAMP and Ca2+ independently modulate CT responses to acidic stimuli. While cAMP enhances TRC apical H+ entry and CT responses to strong acid, an increase in Ca2+ activates NHE-1, and increases neural adaptation to all acidic stimuli.
The Journal of General Physiology, Jul 1, 1988
There is good evidence indicating that ion-transport pathways in the apical regions of lingual ep... more There is good evidence indicating that ion-transport pathways in the apical regions of lingual epithelial cells, including taste bud cells, may play a role in salt taste reception. In this article, we present evidence that, in the case of the dog, there also exists a sugar-activated ion-transport pathway that is linked to sugar taste transduction. Evidence was drawn from two parallel lines of experiments: (a) ion-transport studies on the isolated canine lingual epithelium, and (b) recordings from the canine chorda tympani. The results in vitro showed that both mono-and disaccharides in the mucosal bath stimulate a dose-dependent increase in the short-circuit current over the concentration range coincident with mammalian sugar taste responses. Transepithelial current evoked by glucose, fructose, or sucrose in either 30 mM NaC1 or in Krebs-Henseleit buffer (K-H) was partially blocked by amiloride. Among current carriers activated by saccharides, the current response was greater with Na than with K. Ion flux measurements in K-H during stimulation with 3-O-methylgiucose showed that the sugar-evoked current was due to an increase in the Na influx. Ouabain or amiloride reduced the sugar-evoked Na influx without effect on sugar transport as measured with tritiated 3-O-methylglucose. Amiloride inhibited the canine chorda tympani response to 0.5 M NaC1 by 70-80% and the response to 0.5 M KCI by ~40%. This agreed with the percent inhibition by amiloride of the short-circuit current supported in vitro by NaCI and KC1. Amiloride also partially inhibited the chorda tympani responses to sucrose and to fructose. The results indicate that in the dog: (a) the ion transporter subserving Na taste also subserves part of the response to K, and (b) a sugar-activated, Na-preferring ion-transport system is one mechanism mediating sugar taste transduction. Results in the literature indicate a similar sweet taste mechanism for humans.
The Journal of General Physiology, Nov 1, 1994
Taste sensory responses from the chorda tympani nerve of the rat were recorded with the lingual r... more Taste sensory responses from the chorda tympani nerve of the rat were recorded with the lingual receptive field under current or voltage clamp. Consistent with previous results (Ye, Q.
The Anion Paradox in Sodium Taste Reception: Resolution by Voltage-Clamp Studies
Science, Nov 1, 1991
Sodium salts are potent taste stimuli, but their effectiveness is markedly dependent on the anion... more Sodium salts are potent taste stimuli, but their effectiveness is markedly dependent on the anion, with chloride yielding the greatest response. The cellular mechanisms that mediate this phenomenon are not known. This "anion paradox" has been resolved by considering the field potential that is generated by restricted electrodiffusion of the anion through paracellular shunts between taste-bud cells. Neural responses to sodium chloride, sodium acetate, and sodium gluconate were studied while the field potential was voltage-clamped. Clamping at electronegative values eliminated the anion effect, whereas clamping at electropositive potentials exaggerated it. Thus, field potentials across the lingual epithelium modulate taste reception, indicating that the functional unit of taste reception includes the taste cell and its paracellular microenvironment.
Taste-mixture suppression: functional dissection of cellular and paracellular origins
Journal of Neurophysiology, May 1, 1996
1. Chorda tympani (CT) nerve responses were recorded during simultaneous current and voltage clam... more 1. Chorda tympani (CT) nerve responses were recorded during simultaneous current and voltage clamping of the lingual receptive-field epithelium to examine the role of field potential in taste mixture suppression between sodium gluconate (NaG) and potassium gluconate (KG). 2. Under zero current-clamp conditions, CT responses to 100 mM NaG were suppressed by 63% when presented in mixture with 250 mM KG. At this concentration, KG alone elicited no measurable neural activity, but produced a large submucosal-positive field potential. 3. When CT responses to 100 mM NaG were obtained with voltage clamp at the zero-current clamp field potential of the NaG/KG mixture, they were suppressed by only 30% relative to NaG responses under zero-current clamp. Similarly, CT responses to the mixture of NaG and KG measured while voltage was clamped at the field potential of NaG alone were slightly elevated, but not to the magnitude of zero-current clamp responses to NaG. Therefore field potential-mediated suppression of CT responses to NaG accounts for only a part of the total mixture suppression between NaG and KG. 4. Analysis of the voltage dependence of CT responses to NaG indicated that the moderate field potential increase (8.9 mV) caused by the presence of KG in the mixture equates to a 43% increase in the apparent Km for NaG, from 110 to 157 mM. Use of this effective Km obviated the effect of field potential on CT responses to the NaG/KG mixture and permitted kinetic analysis of K+ blockade of Na+ responses. These analyses suggested that K ions block Na+ movement through apical Na+ channels in a voltage-independent manner with an apparent Ko of 405 mM. Importantly, direct inhibition of Na+ transduction by K+ can account for the part of mixture suppression not mediated by field potential. 5. These experiments reveal that mixture suppression between NaG and KG is derived from two distinct sources. Field potential, triggered largely by the limited mobility of both K+ and Na+ through taste bud tight junctions, globally modulates Na+ transduction. In addition, at the level of the apical Na+ channel, K ions directly block movement of depolarizing Na+ across taste receptor apical membranes.
Journal of Neurophysiology, Feb 1, 1998
Self-inhibition in Ca 2/-evoked taste receptors: a novel tool for (AIC) of the NaCl neural respon... more Self-inhibition in Ca 2/-evoked taste receptors: a novel tool for (AIC) of the NaCl neural response arises from transduction functional dissection of salt taste transduction mechanisms. J. Neusites along the basolateral membranes of receptor cells, acrophysiol. 79: 911-921, 1998. Rat chorda tympani (CT) responses cess to which is assumed to be through paracellular pathways to CaCl 2 were obtained during simultaneous current and voltage (Elliot and Simon 1990; Mierson et al. 1996; Simon et al. clamping of the lingual receptive field. Unlike most other salts, 1993; Stewart et al. 1995; Ye et al. 1993). The principal CaCl 2 induced negatively directed transepithelial potentials and barriers in these pathways are the TJs that connect the apical gave CT responses that were auto-inhibitory beyond a critical conpoles of the taste receptor cells, which act as weakly cationcentration. CT responses increased in a dose-dependent manner to Ç0.3 M, whereafter they decreased with increasing concentration. selective barriers (DeSimone et al. 1984; Simon and Garvin At concentrations where Ca 2/ was self-inhibitory, it also inhibited 1985; Ye et al. 1993). In addition, these pathways likely responses to NaCl, KCl, and NH 4 Cl present in mixtures with CaCl 2. participate in K / and NH / 4 salt taste responses (Kloub et Ca 2/ completely blocked the amiloride-insensitive component of al. 1997; Ye at al. 1994). If so, transduction sites for NaCl, the NaCl CT response, the entire KCl-evoked CT response, and KCl, and NH 4 Cl may be accessible only by means of a the high-concentration-domain CT responses of NH 4 Cl (¢0.3 M). common pathway across the TJ complex. However, until The overlapping Ca 2/-sensitivity between the responses of the now, a reliable means of probing paracellular pathways, inthree Cl 0 salts (Na / , K / , and NH / 4) suggests a common, Ca 2/volved in taste reception, has been unavailable. sensitive, transduction pathway. Extracellular Ca 2/ has been shown to modulate the paracellular pathways in different epithelial cell Calcium modulation of TJs has been documented in varilines by decreasing the water permeability and cation conductance ous epithelia. Removing it increases the permeability of the of tight junctions. Ca 2/-induced modulation of tight junctions is rat intestine (Tidball 1964), opens the junctional complex associated with Ca 2/ binding to fixed negative sites. This results between the oxyntic cells (Sedar and Forte 1964) and panin a conversion of ion selectivity from cationic to anionic, which creatic acinar cells (Meldolesi et al. 1978), and produces we also observed in our system through simultaneous monitoring fragmentation of the TJs in mammary glands (Pitelka et al. of the transepithelial potential during CT recording. The data indi-1983). Removal of Ca 2/ from the medium of Madin-Darby cate the paracellular pathway as the stimulatory and modulatory canine monolayer cells opens their TJs, and its subsequent site of CaCl 2 taste responses. In addition, they indicate that imrestoration causes them to reseal (Martinez-Palmo et al. portant transduction sites for NaCl, KCl, and NH 4 Cl taste reception are accessible only through the paracellular pathways. More gener-1980). Ca 2/ triggers the sealing of TJs at a critical concenally, they show that modulation of paracellular transport by Ca 2/ tration by acting on an extracellular site (Contreras et al. in an intact epithelium has functional consequences at a systemic 1991). TJ permeability has been correlated with changes in level.
Biophysical Journal, Mar 1, 1980
Excitatory responses recorded from vertebrate olfactory sensory neurons are characterized by long... more Excitatory responses recorded from vertebrate olfactory sensory neurons are characterized by long latencies compared with those from other sensory receptors. Explanations which assume free access of the stimuli to receptor molecules presumably located on the olfactory cilia necessarily imply an intrinsic delay in the transduction mechanism. In contrast, the possibility of restricted or delayed access due to diffusion of the stimulus to molecular receptors located on the dendritic knob or proximal portions of the cilia suggests transduction processes having time courses similar to those in other sensory systems. We show that the threshold stimulus concentration and the latency of the excitatory response of the salamander can be predicted primarily on the basis of a diffusional delay and that the receptor molecules are well below the surface of the mucus. Examination of response latencies for other species reported in the literature support the generality of diffusional delay. The predicted location of molecular receptor sites is largely insensitive to assumptions based on the mode of clearance of the stimuli. Additional access restrictions are discussed but are shown to generate qualitatively different latency functions than does diffusion, suggesting that they exert only minor influences on latency and threshold characteristics.
A Surface Chemical Model of Salt, Acid, and "Water" Taste
Advances in chemistry series, Jun 1, 1980
An analysis of the effects of stimulus transport and membrane charge on the salt, acid and water-response of mammals
Chemical Senses, 1980
Abstract. We present an analysis of stimulus transport in mammalian taste reception emphasizing t... more Abstract. We present an analysis of stimulus transport in mammalian taste reception emphasizing the coupling between hydrodynamic and diffusive mass transfer. We show that flow-rate dependence in the phasic portions of the gustatory response can be explained by a flow-velocity dependent diffusion-boundary layer in series with a flow-indifferent path length. Using data from the literature we show that the concentration dependence of the neural latency to NaCl stimulation in the rat and the threshold concentration can be accounted for by the time course of stimulus arrival and need not imp-ly a uniquely slow sensory transduction process. We develop a generalized response function which describes aspects of the early phasic neural response and shows that early events are governed solely by the local concentration of stimulus. This too is confirmed by data in the literature. The surface pressure is characterized as an example of a nonmonotonic response function which can account for the general properties of the salt, acid and water response. In vitro studies on phopholipid monolayers conform to the theory. It is suggested that surface activity may be critical in transduction and that sur-face active agents can have profound effects on taste reception.
Voltage dependence of the rat chorda tympani response to Na+ salts: implications for the functional organization of taste receptor cells
Journal of Neurophysiology, Jul 1, 1993
1. Voltage-clamp and current-clamp data were obtained from a circumscribed region of the anterior... more 1. Voltage-clamp and current-clamp data were obtained from a circumscribed region of the anterior rat lingual epithelium while simultaneously monitoring the afferent, stimulus-evoked, neural response from the same receptive field. 2. Chorda tympani (CT) responses at constant Na(+)-salt concentration were enhanced by submucosa negative voltage clamp and suppressed by positive voltage clamp. The complete CT response profile, including the time course of adaptation, was not uniquely determined by NaCl concentration alone. The response could be reproduced at different NaCl concentrations by applying a compensating voltage. 3. The form of the concentration and voltage dependence of the CT response indicates that the complete stimulus energy is the Na+ electrochemical potential difference across receptor cell apical membranes, and not Na+ concentration alone. This is the underlying principal behind the equivalence of chemical and electric taste for Na+ salts. 4. CT responses to sodium gluconate (25 and 200 mM) and 25 mM NaCl produced amiloride-insensitive components (AIC) of low magnitude. NaCl at 200 mM produced a significantly larger AIC. The AIC was voltage-clamp independent. The relative magnitude of the AIC was positively correlated with the transepithelial conductance of each salt. This suggests that the large AIC for 200 mM NaCl results from its relatively high permeability through the paracellular pathway. 5. Analysis of the CT response under voltage clamp revealed two anion effects on Na(+)-salt taste, both of which act through the paracellular shunt. 1) Anions modify the transepithelial potential (TP) across tight junctions and thereby modulate the cell receptor potential. This anion effect can be eliminated by voltage clamping the TP. 2) Sufficiently mobile anions facilitate electroneutral diffusion of Na+ salts through tight junctions. This effect is observed especially when Cl- is the anion and when the stimulus concentration favors NaCl influx, allowing Na+ to stimulate receptor cells from the submucosal side. Because the submucosal intercellular spaces are nearly isopotential regions, this effect is insensitive to voltage clamp of the TP. The large AIC associated with this anion effect is due to the low permeability of amiloride.
Chemical Senses, May 7, 2015
Modulatory effects of pH i and [Ca 2+ ] i on taste receptor cell (TRC) epithelial sodium channel ... more Modulatory effects of pH i and [Ca 2+ ] i on taste receptor cell (TRC) epithelial sodium channel (ENaC) were investigated by monitoring chorda tympani (CT) responses to NaCl and KCl at various lingual voltages, before and after lingual application of ionomycin and with 0-10 mM CaCl 2 in the stimulus and rinse solutions adjusted to pH o 2.0-9.7. 0.1 and 0.5 M KCl responses varied continuously with voltage and were fitted to an apical ion channel kinetic model using the same parameters. ENaC-dependent NaCl CT response was fitted to the same channel model but with parameters characteristic of ENaC. A graded increase in TRC [Ca 2+ ] i decreased the ENaC-dependent NaCl CT response, and inhibited and ultimately eliminated its pH sensitivity. CT responses to KCl were pH i-and [Ca 2+ ] i-independent. Between ±60 mV applied lingual potential, the data were well described by a linear approximation to the nonlinear channel equation and yielded 2 parameters, the open-circuit response and the negative of the slope of the line in the CT response versus voltage plot, designated the response conductance. The ENaC-dependent NaCl CT response conductance was a linear function of the open-circuit response for all pH i-[Ca 2+ ] i combinations examined. Analysis of these data shows that pH i and [Ca 2+ ] i regulate TRC ENaC exclusively through modulation of the maximum CT response.
Electrophysiological studies of salt-sensitive taste receptors
Experimental data indicate that the Na ion taste receptor is a Na selective membrane ion channel.... more Experimental data indicate that the Na ion taste receptor is a Na selective membrane ion channel. This channel appears to have passive properties (it is not voltage-gated). Sodium ions stimulate receptor cells by entering them directly down a favorable electrochemical potential gradient and thereby depolarizing the cells. This presumably leads to the release of neurotransmitter, thereby causing excitation of the taste nerves. This process may require the intervention of voltage-gated Na channels that may depolarize the cells sufficiently to activate Ca channels necessary for Ca entry into the cells prior to the release of neurotransmitter. Anions may either augment or impede the movement of Na, depending on their paracellular permeabilities. The electrical potential across the taste buds, controlled in part by anion permeability across the tight junctions, may be one of the regulatory factors in the release of neurotransmitter.<<ETX>>
Involvement of NADPH-Dependent and cAMP-PKA Sensitive H+ Channels in the Chorda Tympani Nerve Responses to Strong Acids
Chemical Senses, Feb 21, 2011
Dietary Na(+)-restriction prevents development of functional Na+ channels in taste cell apical membranes: proof by in vivo membrane voltage perturbation
Journal of Neurophysiology, Oct 1, 1993
1. Chorda tympani (CT) neural responses to NaCl were recorded while the potential across the apic... more 1. Chorda tympani (CT) neural responses to NaCl were recorded while the potential across the apical membrane of taste cells was perturbed by voltage clamp in rats fed a Na(+)-restricted diet pre- and postnatally (Na(+)-restricted rats) and in controls. 2. Control rats gave CT responses that were enhanced at negative voltage clamp and suppressed at positive voltage clamp. In contrast, CT responses from Na(+)-restricted rats were virtually voltage insensitive. 3. Analysis of the voltage-sensitivity of the CT response shows that Na(+)-restricted rats have < 10% of the density of functional apical Na+ channels normally present in control rats demonstrating that early dietary Na(+)-restriction prevents the functional expression of these key elements in salt taste transduction. Furthermore, the data demonstrate the value of this technique in assessing involvement of distinct cellular domains in taste transduction.
Surface active taste modifiers: a comparison of the physical and psychophysical properties of gymnemic acid and sodium lauryl sulfate
Chemical Senses, 1980
Abstract We have compared the surface active properties of gymnemic acid with those of the wellkn... more Abstract We have compared the surface active properties of gymnemic acid with those of the wellknown surfactant sodium lauryl sulfate. Aqueous solutions of gymnemic acid produce a surface tension-concentration relation similar to that of water soluble surfactants. Its form ...
The Journal of General Physiology, May 1, 1984
The electrophysiological properties of the dorsal and ventral canine lingual epithelium are studi... more The electrophysiological properties of the dorsal and ventral canine lingual epithelium are studied in vitro. The dorsal epithelium contains a special ion transport system activated by mucosal solutions hyperosmotic in NaCl or LiCl. Hyperosmotic KCl is significantly less effective as an activator of this system. The lingual frenulum does not contain the transport system. In the dorsal surface it is characterized by a rapid increase in inward current and can be quantitated as a second component in the time course of either the opencircuit potential or short-circuit current when the mucosal solution is hyperosmotic in NaCl or LiCl. The increased inward current (hyperosmotic response) can be eliminated by amiloride (10' M). The specific location of this transport system in the dorsal surface and the fact that it operates over the concentration range characteristic of mammalian salt taste suggests a possible link to gustatory transduction. This possibility is tested by recording neural responses in the rat to NaCl and KCl over a concentration range including the hyperosmotic. We demonstrate that amiloride specifically blocks the response to NaCl over the hyperosmotic range while affecting the KCl response significantly less. The results suggest that gustatory transduction for NaCl is mediated by Na entry into the taste cells via the same amiloride-sensitive pathway responsible for the hyperosmotic response in vitro. Further studies of the in vitro system give evidence for paracellular as well as transcellular current paths. The transmural current-voltage relations are linear under both symmetrical and asymmetrical conditions. After ouabain treatment under symmetrical conditions, the shortcircuit current decays to zero. The increase in resistance, though significant, is small, which suggests a sizeable shunt pathway for current. Flux measurements show that sodium is absorbed under symmetrical conditions. Mucosal solutions hyperosmotic in various sugars also induce an amiloride-sensitive inward current. In summary, this work provides evidence that the sodium taste receptor is most probably a sodium transport system, specifically adapted to the dorsal surface of the tongue. The transport paradigm of gustation also suggests a simple model for electric taste and possible mechanisms for sweet taste .
Evidence for electrogenic active ion transport across the frog olfactory mucosa in vitro
Chemical Senses, 1984
ABSTRACT
PLOS ONE, May 19, 2014
The effects of small molecule ENaC activators N,N,N-trimethyl-2-((4-methyl-2-((4-methyl-1H-indol-... more The effects of small molecule ENaC activators N,N,N-trimethyl-2-((4-methyl-2-((4-methyl-1H-indol-3-yl)thio)pentanoyl)oxy)ethanaminium iodide (Compound 1) and N-(2-hydroxyethyl)-4-methyl-2-((4-methyl-1H-indol-3-yl)thio)pentanamide (Compound 2), were tested on the benzamil (Bz)-sensitive NaCl chorda tympani (CT) taste nerve response under opencircuit conditions and under 660 mV applied lingual voltage-clamp, and compared with the effects of known physiological activators (8-CPT-cAMP, BAPTA-AM, and alkaline pH), and an inhibitor (ionomycin+Ca 2+) of ENaC. The NaCl CT response was enhanced at 260 mV and suppressed at +60 mV. In every case the CT response (r) versus voltage (V) curve was linear. All ENaC activators increased the open-circuit response (r o) and the voltage sensitivity (k, negative of the slope of the r versus V curve) and ionomycin+Ca 2+ decreased r o and k to zero. Compound 1 and Compound 2 expressed a sigmoidal-saturating function of concentration (0.25-1 mM) with a half-maximal response concentration (k) of 0.49 and 1.05 mM, respectively. Following treatment with 1 mM Compound 1, 8-CPT-cAMP, BAPTA-AM and pH 10.3, the Bz-sensitive NaCl CT response to 100 mM NaCl was enhanced and was equivalent to the Bz-sensitive CT response to 300 mM NaCl. Plots of k versus r o in the absence and presence of the activators or the inhibitor were linear, suggesting that changes in the affinity of Na + for ENaC under different conditions are fully compensated by changes in the apical membrane potential difference, and that the observed changes in the Bz-sensitive NaCl CT response arise exclusively from changes in the maximum CT response (r m). The results further suggest that the agonists enhance and ionomycin+Ca 2+ decreases ENaC function by increasing or decreasing the rate of release of Na + from its ENaC binding site to the receptor cell cytosol, respectively. Irrespective of agonist type, the Bz-sensitive NaCl CT response demonstrated a maximum response enhancement limit of about 75% over control value.
Journal of Neurophysiology, Mar 1, 1997
psychophysical studies have suggested simi-Chorda tympani responses under lingual voltage clamp: ... more psychophysical studies have suggested simi-Chorda tympani responses under lingual voltage clamp: implicalarities in the taste quality profiles of NH 4 Cl and KCl. In tions for NH 4 salt taste transduction. J. Neurophysiol. 77: 1393addition, functional similarities at the level of nucleus tractus 1406, 1997. Rat chorda tympani (CT) responses to NH 4 Cl, ammosolitarius for NH / 4 and K / salts have been suggested (Nakanium acetate (NH 4 Ac), and ammonium hippurate (NH 4 Hp) were mura and Norgren 1993). NH / 4 and K / ions have similar obtained during simultaneous current and voltage clamping of the hydrated radii and ionic conductances in free solution (Kneplingual field potential. Although functional and developmental simper et al. 1989). These ions may also have similar properties ilarities for gustation have been reported for NH / 4 and K / salts, at the cell membrane level, e.g., NH / 4 has been found to we report here that significant differences are discernible in the CT responses to both salts. Unlike neural responses to KCl, those substitute for K / on transporters in many cell types (Amlal to NH 4 Cl are voltage sensitive, enhanced by submucosa negative et al. 1994; Kinne et al. 1986; Tsuruoka et al. 1993). and suppressed by positive voltage clamp. In this regard, NH 4 Cl Developmental studies of salt taste in neonatal rats responses are qualitatively similar to NaCl responses; however, the show that CT responses to NH 4 Cl are fully developed magnitude of NH 4 Cl voltage sensitivity is significantly less than before those to NaCl (Hill et al. 1982; Mistretta and that of NaCl. The concentration dependence of the CT response Bradley 1980; Yamada 1980). Recordings from more to NH 4 Cl manifests a biphasic nonlinear relationship not observed central loci in the taste neuraxis, in the nucleus tractus with KCl or NaCl. Below 0.3 M, the CT response increases as if to solitarius (Hill et al. 1983) , and in cortical taste areas approach a saturation value. However, beyond 0.3 M an inflection (Ogawa et al. 1994) are generally consistent with this. appears in the CT-concentration curve because of an abrupt increase in CT responses. This kinetic profile is Cl 0 dependent and The different maturation rates for NaCl and NH 4 Cl neural is correlated with an increase in transepithelial conductance that responses suggest that taste receptors for NH / 4 and Na / displays similar NH 4 Cl concentration dependence. The biphasic are, at least in part, functionally distinct. A recent study relation to salt concentration is not observed when acetate or hipindicates that K / salt CT responses are mediated by a purate is substituted for Cl 0. As with Na / and K / salts, less single, diffusion-controlled voltage-insensitive transducmobile anions than Cl 0 (Ac 0 and Hp 0) lower the CT responses. tion mechanism (Ye et al. 1994). K / salt taste responses However, like Na / salts, but in contrast to K / salts, the onset occur via a sub-tight junctional transducer for K / ions kinetics of CT responses to NH 4 Ac or NH 4 Hp remain rapid, even with access limited by anion mobility. In contrast, NaCl under positive voltage-clamp conditions. Amiloride (100 mM) partially suppresses CT responses within the concentration range of CT responses consist of a voltage-dependent (amiloride-0.05-0.3 M (48-20% suppression). Amiloride also suppresses sensitive) component and smaller voltage-independent the voltage sensitivity of NH 4 Cl CT responses, but does not elimi-(amiloride-insensitive) component (Ye et al. 1993). The nate that sensitivity as it does for Na / salts. In conclusion, the data amiloride and voltage sensitivity suggests that this Na suggest that taste transduction for NH 4 salts is mediated over two taste transducing element is an apical membrane ion NH / 4 conduction pathways in the taste bud. This is especially evichannel (Avenet and Lindemann 1991; Garty and Benos dent with NH 4 Cl, where the CT-concentration curves show two 1988). The amiloride-insensitive component depends on distinct kinetic regimes. Below 0.3 M the saturation with increasing the presence of Cl 0 in Na salt taste (Elliott and Simon concentration, clamp voltage response dependence, and amiloride 1990; Formaker and Hill 1988; Ye et al. 1993). sensitivity suggest an apical membrane transduction conductance. Above 0.3 M, the high anion dependence of the response and The main objective of this study is to investigate the transits amiloride insensitivity indicate participation of the paracellular duction mechanisms involved in NH / 4 salt taste perception. pathway in transduction. This was accomplished by comparing CT responses to NH / 4 salts, with the use of the in situ lingual voltage-clamp method, with the responses to Na / and K / salts. The results I N T R O D U C T I O N indicate the presence of two transduction mechanisms for NH 4 Cl: an apical NH / 4 ion conductance, dominant with NH 4 Cl has been widely used as a reference stimulus in NH 4 Cl concentrations below Ç0.3 M, and a mechanism acrecordings from different levels of the taste sensory system cessible via the paracellular pathway. The latter is especially in various animal models. These include cortical taste areas prominant in the presence of Cl 0 and with NH / 4 concentra-(Ogawa et al. 1994), the nucleus tractus solitarius (Hill et al. tions ú0.3 M. 1983; Nakamura and Norgren 1993), and the chorda tympani
Journal of Neurophysiology, Sep 1, 2007
The effect of nicotine on the benzamil (Bz)-insensitive (transient receptor potential vanilloid-1... more The effect of nicotine on the benzamil (Bz)-insensitive (transient receptor potential vanilloid-1 variant cation channel, TRPV1t) and the Bzsensitive (epithelial Na ϩ channel, ENaC) salt taste receptors and sour taste was investigated by monitoring intracellular Na ϩ and H ϩ activity (pH i) in polarized fungiform taste receptor cells (TRCs) and the chorda tympani (CT) nerve responses to NaCl, KCl, and HCl. CT responses in Sprague-Dawley rats and both wildtype and TRPV1 knockout (KO) mice were recorded in the presence and absence of agonists [resiniferatoxin (RTX) and elevated temperature] and an antagonist (SB-366791) of TRPV1t, the ENaC blocker (Bz), and varying apical pH (pH o). At concentrations Ͻ0.015 M, nicotine enhanced and at Ͼ0.015 M, it inhibited CT responses to KCl and NaCl. Nicotine produced maximum enhancement in the Bz-insensitive NaCl CT response at pH o between 6 and 7. RTX and elevated temperature increased the sensitivity of the CT response to nicotine in salt-containing media, and SB-366791 inhibited these effects. TRPV1 KO mice demonstrated no Bz-insensitive CT response to NaCl and no sensitivity to nicotine, RTX, and elevated temperature. We conclude that nicotine modulates salt responses by direct interaction with TRPV1t. At pH o Ͼ8, the apical membrane permeability of nicotine was increased significantly, resulting in increase in TRC pH i and volume, activation of ENaC, and enhancement of the Bz-sensitive NaCl CT response. At pH o Ͼ8, nicotine also inhibited the phasic component of the HCl CT response. We conclude that the effects of nicotine on ENaC and the phasic HCl CT response arise from increases in TRC pH i and volume.
The Journal of Physiology, Mar 30, 2004
The role of basolateral Na+–H+ exchanger isoform-1 (NHE-1) was investigated in neural adaptation ... more The role of basolateral Na+–H+ exchanger isoform-1 (NHE-1) was investigated in neural adaptation of rat taste responses to acidic stimuli, by direct measurement of intracellular pH (pHi) in polarized taste receptor cells (TRCs) and by chorda tympani (CT) taste nerve recordings. In TRCs perfused with CO2/HCO3−-free solution (pH 7.4), removal of basolateral Na+ decreased pHi reversibly and zoniporide, a specific NHE-1 blocker, inhibited the Na+-induced changes in pHi. The spontaneous rate of TRC pHi recovery from NH4Cl pulses was inhibited by basolateral zoniporide with a Ki of 0.33μm. Exposure to basolateral ionomycin, reversibly increased TRC Ca2+, resting pHi, and the spontaneous rate of pHi recovery from an NH4Cl pulse. These effects of Ca2+ on pHi were blocked by zoniporide. In in vivo experiments, topical lingual application of zoniporide increased the magnitude of the CT responses to acetic acid and CO2, but not to HCl. Topical lingual application of ionomycin did not affect the phasic part of the CT responses to acidic stimuli, but decreased the tonic part by 50% of control over a period of about 1 min. This increased adaptation in the CT response was inhibited by zoniporide. Topical lingual application of 8-CPT-cAMP increased the CT responses to HCl, but not to CO2, and acetic acid. In the presence of cAMP, ionomycin increased sensory adaptation to HCl, CO2, and acetic acid. Thus, cAMP and Ca2+ independently modulate CT responses to acidic stimuli. While cAMP enhances TRC apical H+ entry and CT responses to strong acid, an increase in Ca2+ activates NHE-1, and increases neural adaptation to all acidic stimuli.
The Journal of General Physiology, Jul 1, 1988
There is good evidence indicating that ion-transport pathways in the apical regions of lingual ep... more There is good evidence indicating that ion-transport pathways in the apical regions of lingual epithelial cells, including taste bud cells, may play a role in salt taste reception. In this article, we present evidence that, in the case of the dog, there also exists a sugar-activated ion-transport pathway that is linked to sugar taste transduction. Evidence was drawn from two parallel lines of experiments: (a) ion-transport studies on the isolated canine lingual epithelium, and (b) recordings from the canine chorda tympani. The results in vitro showed that both mono-and disaccharides in the mucosal bath stimulate a dose-dependent increase in the short-circuit current over the concentration range coincident with mammalian sugar taste responses. Transepithelial current evoked by glucose, fructose, or sucrose in either 30 mM NaC1 or in Krebs-Henseleit buffer (K-H) was partially blocked by amiloride. Among current carriers activated by saccharides, the current response was greater with Na than with K. Ion flux measurements in K-H during stimulation with 3-O-methylgiucose showed that the sugar-evoked current was due to an increase in the Na influx. Ouabain or amiloride reduced the sugar-evoked Na influx without effect on sugar transport as measured with tritiated 3-O-methylglucose. Amiloride inhibited the canine chorda tympani response to 0.5 M NaC1 by 70-80% and the response to 0.5 M KCI by ~40%. This agreed with the percent inhibition by amiloride of the short-circuit current supported in vitro by NaCI and KC1. Amiloride also partially inhibited the chorda tympani responses to sucrose and to fructose. The results indicate that in the dog: (a) the ion transporter subserving Na taste also subserves part of the response to K, and (b) a sugar-activated, Na-preferring ion-transport system is one mechanism mediating sugar taste transduction. Results in the literature indicate a similar sweet taste mechanism for humans.
The Journal of General Physiology, Nov 1, 1994
Taste sensory responses from the chorda tympani nerve of the rat were recorded with the lingual r... more Taste sensory responses from the chorda tympani nerve of the rat were recorded with the lingual receptive field under current or voltage clamp. Consistent with previous results (Ye, Q.
The Anion Paradox in Sodium Taste Reception: Resolution by Voltage-Clamp Studies
Science, Nov 1, 1991
Sodium salts are potent taste stimuli, but their effectiveness is markedly dependent on the anion... more Sodium salts are potent taste stimuli, but their effectiveness is markedly dependent on the anion, with chloride yielding the greatest response. The cellular mechanisms that mediate this phenomenon are not known. This "anion paradox" has been resolved by considering the field potential that is generated by restricted electrodiffusion of the anion through paracellular shunts between taste-bud cells. Neural responses to sodium chloride, sodium acetate, and sodium gluconate were studied while the field potential was voltage-clamped. Clamping at electronegative values eliminated the anion effect, whereas clamping at electropositive potentials exaggerated it. Thus, field potentials across the lingual epithelium modulate taste reception, indicating that the functional unit of taste reception includes the taste cell and its paracellular microenvironment.
Taste-mixture suppression: functional dissection of cellular and paracellular origins
Journal of Neurophysiology, May 1, 1996
1. Chorda tympani (CT) nerve responses were recorded during simultaneous current and voltage clam... more 1. Chorda tympani (CT) nerve responses were recorded during simultaneous current and voltage clamping of the lingual receptive-field epithelium to examine the role of field potential in taste mixture suppression between sodium gluconate (NaG) and potassium gluconate (KG). 2. Under zero current-clamp conditions, CT responses to 100 mM NaG were suppressed by 63% when presented in mixture with 250 mM KG. At this concentration, KG alone elicited no measurable neural activity, but produced a large submucosal-positive field potential. 3. When CT responses to 100 mM NaG were obtained with voltage clamp at the zero-current clamp field potential of the NaG/KG mixture, they were suppressed by only 30% relative to NaG responses under zero-current clamp. Similarly, CT responses to the mixture of NaG and KG measured while voltage was clamped at the field potential of NaG alone were slightly elevated, but not to the magnitude of zero-current clamp responses to NaG. Therefore field potential-mediated suppression of CT responses to NaG accounts for only a part of the total mixture suppression between NaG and KG. 4. Analysis of the voltage dependence of CT responses to NaG indicated that the moderate field potential increase (8.9 mV) caused by the presence of KG in the mixture equates to a 43% increase in the apparent Km for NaG, from 110 to 157 mM. Use of this effective Km obviated the effect of field potential on CT responses to the NaG/KG mixture and permitted kinetic analysis of K+ blockade of Na+ responses. These analyses suggested that K ions block Na+ movement through apical Na+ channels in a voltage-independent manner with an apparent Ko of 405 mM. Importantly, direct inhibition of Na+ transduction by K+ can account for the part of mixture suppression not mediated by field potential. 5. These experiments reveal that mixture suppression between NaG and KG is derived from two distinct sources. Field potential, triggered largely by the limited mobility of both K+ and Na+ through taste bud tight junctions, globally modulates Na+ transduction. In addition, at the level of the apical Na+ channel, K ions directly block movement of depolarizing Na+ across taste receptor apical membranes.
Journal of Neurophysiology, Feb 1, 1998
Self-inhibition in Ca 2/-evoked taste receptors: a novel tool for (AIC) of the NaCl neural respon... more Self-inhibition in Ca 2/-evoked taste receptors: a novel tool for (AIC) of the NaCl neural response arises from transduction functional dissection of salt taste transduction mechanisms. J. Neusites along the basolateral membranes of receptor cells, acrophysiol. 79: 911-921, 1998. Rat chorda tympani (CT) responses cess to which is assumed to be through paracellular pathways to CaCl 2 were obtained during simultaneous current and voltage (Elliot and Simon 1990; Mierson et al. 1996; Simon et al. clamping of the lingual receptive field. Unlike most other salts, 1993; Stewart et al. 1995; Ye et al. 1993). The principal CaCl 2 induced negatively directed transepithelial potentials and barriers in these pathways are the TJs that connect the apical gave CT responses that were auto-inhibitory beyond a critical conpoles of the taste receptor cells, which act as weakly cationcentration. CT responses increased in a dose-dependent manner to Ç0.3 M, whereafter they decreased with increasing concentration. selective barriers (DeSimone et al. 1984; Simon and Garvin At concentrations where Ca 2/ was self-inhibitory, it also inhibited 1985; Ye et al. 1993). In addition, these pathways likely responses to NaCl, KCl, and NH 4 Cl present in mixtures with CaCl 2. participate in K / and NH / 4 salt taste responses (Kloub et Ca 2/ completely blocked the amiloride-insensitive component of al. 1997; Ye at al. 1994). If so, transduction sites for NaCl, the NaCl CT response, the entire KCl-evoked CT response, and KCl, and NH 4 Cl may be accessible only by means of a the high-concentration-domain CT responses of NH 4 Cl (¢0.3 M). common pathway across the TJ complex. However, until The overlapping Ca 2/-sensitivity between the responses of the now, a reliable means of probing paracellular pathways, inthree Cl 0 salts (Na / , K / , and NH / 4) suggests a common, Ca 2/volved in taste reception, has been unavailable. sensitive, transduction pathway. Extracellular Ca 2/ has been shown to modulate the paracellular pathways in different epithelial cell Calcium modulation of TJs has been documented in varilines by decreasing the water permeability and cation conductance ous epithelia. Removing it increases the permeability of the of tight junctions. Ca 2/-induced modulation of tight junctions is rat intestine (Tidball 1964), opens the junctional complex associated with Ca 2/ binding to fixed negative sites. This results between the oxyntic cells (Sedar and Forte 1964) and panin a conversion of ion selectivity from cationic to anionic, which creatic acinar cells (Meldolesi et al. 1978), and produces we also observed in our system through simultaneous monitoring fragmentation of the TJs in mammary glands (Pitelka et al. of the transepithelial potential during CT recording. The data indi-1983). Removal of Ca 2/ from the medium of Madin-Darby cate the paracellular pathway as the stimulatory and modulatory canine monolayer cells opens their TJs, and its subsequent site of CaCl 2 taste responses. In addition, they indicate that imrestoration causes them to reseal (Martinez-Palmo et al. portant transduction sites for NaCl, KCl, and NH 4 Cl taste reception are accessible only through the paracellular pathways. More gener-1980). Ca 2/ triggers the sealing of TJs at a critical concenally, they show that modulation of paracellular transport by Ca 2/ tration by acting on an extracellular site (Contreras et al. in an intact epithelium has functional consequences at a systemic 1991). TJ permeability has been correlated with changes in level.
Biophysical Journal, Mar 1, 1980
Excitatory responses recorded from vertebrate olfactory sensory neurons are characterized by long... more Excitatory responses recorded from vertebrate olfactory sensory neurons are characterized by long latencies compared with those from other sensory receptors. Explanations which assume free access of the stimuli to receptor molecules presumably located on the olfactory cilia necessarily imply an intrinsic delay in the transduction mechanism. In contrast, the possibility of restricted or delayed access due to diffusion of the stimulus to molecular receptors located on the dendritic knob or proximal portions of the cilia suggests transduction processes having time courses similar to those in other sensory systems. We show that the threshold stimulus concentration and the latency of the excitatory response of the salamander can be predicted primarily on the basis of a diffusional delay and that the receptor molecules are well below the surface of the mucus. Examination of response latencies for other species reported in the literature support the generality of diffusional delay. The predicted location of molecular receptor sites is largely insensitive to assumptions based on the mode of clearance of the stimuli. Additional access restrictions are discussed but are shown to generate qualitatively different latency functions than does diffusion, suggesting that they exert only minor influences on latency and threshold characteristics.
A Surface Chemical Model of Salt, Acid, and "Water" Taste
Advances in chemistry series, Jun 1, 1980
An analysis of the effects of stimulus transport and membrane charge on the salt, acid and water-response of mammals
Chemical Senses, 1980
Abstract. We present an analysis of stimulus transport in mammalian taste reception emphasizing t... more Abstract. We present an analysis of stimulus transport in mammalian taste reception emphasizing the coupling between hydrodynamic and diffusive mass transfer. We show that flow-rate dependence in the phasic portions of the gustatory response can be explained by a flow-velocity dependent diffusion-boundary layer in series with a flow-indifferent path length. Using data from the literature we show that the concentration dependence of the neural latency to NaCl stimulation in the rat and the threshold concentration can be accounted for by the time course of stimulus arrival and need not imp-ly a uniquely slow sensory transduction process. We develop a generalized response function which describes aspects of the early phasic neural response and shows that early events are governed solely by the local concentration of stimulus. This too is confirmed by data in the literature. The surface pressure is characterized as an example of a nonmonotonic response function which can account for the general properties of the salt, acid and water response. In vitro studies on phopholipid monolayers conform to the theory. It is suggested that surface activity may be critical in transduction and that sur-face active agents can have profound effects on taste reception.
Voltage dependence of the rat chorda tympani response to Na+ salts: implications for the functional organization of taste receptor cells
Journal of Neurophysiology, Jul 1, 1993
1. Voltage-clamp and current-clamp data were obtained from a circumscribed region of the anterior... more 1. Voltage-clamp and current-clamp data were obtained from a circumscribed region of the anterior rat lingual epithelium while simultaneously monitoring the afferent, stimulus-evoked, neural response from the same receptive field. 2. Chorda tympani (CT) responses at constant Na(+)-salt concentration were enhanced by submucosa negative voltage clamp and suppressed by positive voltage clamp. The complete CT response profile, including the time course of adaptation, was not uniquely determined by NaCl concentration alone. The response could be reproduced at different NaCl concentrations by applying a compensating voltage. 3. The form of the concentration and voltage dependence of the CT response indicates that the complete stimulus energy is the Na+ electrochemical potential difference across receptor cell apical membranes, and not Na+ concentration alone. This is the underlying principal behind the equivalence of chemical and electric taste for Na+ salts. 4. CT responses to sodium gluconate (25 and 200 mM) and 25 mM NaCl produced amiloride-insensitive components (AIC) of low magnitude. NaCl at 200 mM produced a significantly larger AIC. The AIC was voltage-clamp independent. The relative magnitude of the AIC was positively correlated with the transepithelial conductance of each salt. This suggests that the large AIC for 200 mM NaCl results from its relatively high permeability through the paracellular pathway. 5. Analysis of the CT response under voltage clamp revealed two anion effects on Na(+)-salt taste, both of which act through the paracellular shunt. 1) Anions modify the transepithelial potential (TP) across tight junctions and thereby modulate the cell receptor potential. This anion effect can be eliminated by voltage clamping the TP. 2) Sufficiently mobile anions facilitate electroneutral diffusion of Na+ salts through tight junctions. This effect is observed especially when Cl- is the anion and when the stimulus concentration favors NaCl influx, allowing Na+ to stimulate receptor cells from the submucosal side. Because the submucosal intercellular spaces are nearly isopotential regions, this effect is insensitive to voltage clamp of the TP. The large AIC associated with this anion effect is due to the low permeability of amiloride.
Chemical Senses, May 7, 2015
Modulatory effects of pH i and [Ca 2+ ] i on taste receptor cell (TRC) epithelial sodium channel ... more Modulatory effects of pH i and [Ca 2+ ] i on taste receptor cell (TRC) epithelial sodium channel (ENaC) were investigated by monitoring chorda tympani (CT) responses to NaCl and KCl at various lingual voltages, before and after lingual application of ionomycin and with 0-10 mM CaCl 2 in the stimulus and rinse solutions adjusted to pH o 2.0-9.7. 0.1 and 0.5 M KCl responses varied continuously with voltage and were fitted to an apical ion channel kinetic model using the same parameters. ENaC-dependent NaCl CT response was fitted to the same channel model but with parameters characteristic of ENaC. A graded increase in TRC [Ca 2+ ] i decreased the ENaC-dependent NaCl CT response, and inhibited and ultimately eliminated its pH sensitivity. CT responses to KCl were pH i-and [Ca 2+ ] i-independent. Between ±60 mV applied lingual potential, the data were well described by a linear approximation to the nonlinear channel equation and yielded 2 parameters, the open-circuit response and the negative of the slope of the line in the CT response versus voltage plot, designated the response conductance. The ENaC-dependent NaCl CT response conductance was a linear function of the open-circuit response for all pH i-[Ca 2+ ] i combinations examined. Analysis of these data shows that pH i and [Ca 2+ ] i regulate TRC ENaC exclusively through modulation of the maximum CT response.
Electrophysiological studies of salt-sensitive taste receptors
Experimental data indicate that the Na ion taste receptor is a Na selective membrane ion channel.... more Experimental data indicate that the Na ion taste receptor is a Na selective membrane ion channel. This channel appears to have passive properties (it is not voltage-gated). Sodium ions stimulate receptor cells by entering them directly down a favorable electrochemical potential gradient and thereby depolarizing the cells. This presumably leads to the release of neurotransmitter, thereby causing excitation of the taste nerves. This process may require the intervention of voltage-gated Na channels that may depolarize the cells sufficiently to activate Ca channels necessary for Ca entry into the cells prior to the release of neurotransmitter. Anions may either augment or impede the movement of Na, depending on their paracellular permeabilities. The electrical potential across the taste buds, controlled in part by anion permeability across the tight junctions, may be one of the regulatory factors in the release of neurotransmitter.<<ETX>>