Capsaicin differentially modulates voltage-activated calcium channel currents in dorsal root ganglion neurones of rats (original) (raw)
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Journal of the Peripheral Nervous System, 2007
Modulation of intracellular calcium ([Ca 2þ ] i ) has a major impact on processing of nociceptive signals. While activation of the transient receptor potential vanilloid-1 (TRPV-1) receptor/channel complex increases [Ca 2þ ] i by Ca 2þ entry from the extracellular space, as well as by Ca 2þ release from intracellular stores, the Ca 2þ entry through voltageactivated calcium channels (VACCs) is modulated simultaneously. To clarify the relations between [Ca 2þ ] i and the activation of TRPV-1 receptor and VACC currents [I TRPV-1 and I Ca(V) ], we performed voltage clamp experiments using Ba 2þ as well as Ca 2þ as a charge carrier. The TRPV-1 receptor was activated by the application of 0.5 mM capsaicin, and the currents through TRPV-1 and VACC [I TRPV-1 and I Ca(V) ] were measured either when Ca 2þ release from intracellular stores was pharmacologically promoted or prevented. With Ba 2þ as the divalent charge carrier, capsaicin (0.5 mM) reduced I Ca(V) (elicited by a depolarization to 0 mV) to 52.7 AE 4.5% of baseline, and the elicited current through the TRPV-1 receptor/ channel complex was 6.6 AE 0.9% [relative to peak I Ca(V) ]. These currents were significantly different when Ca 2þ was used as charge carrier: the I Ca(V) reductions were decreased to 17.8 AE 5.9% of baseline, while the I TRPV-1 was as high as 57.1 AE 9.1% of I Ca(V) . Increases of [Ca 2þ ] i by releasing Ca 2þ from intracellular stores (using caffeine, 10 mM) before the application of capsaicin increased the I TRPV-1 (14.1 AE 7%), while the I Ca(V) was decreased to 51.6 AE 4.9% compared with control. A preexperimental partial reduction of the Ca 2þ release from the stores by dantrolene (5 mM) resulted in less pronounced effects [24.5 AE 8.8%, relative to peak I Ca(V) ] for I TRPV-1 , and a reduction to 35.4 AE 3% of baseline for I Ca(V) after capsaicin application.
The Journal of Physiology, 1997
1. Capsaicin and protons cause excitation and sensitization of primary nociceptive afferents. In a subset of dorsal root ganglion (DRG) neurones, which probably represent nociceptive neurones, both capsaicin and protons induce slowly inactivating non-selective cation currents. Whole-cell as well as single channel currents activated by these two stimuli share many biophysical and physiological properties in these neurones. This has lead to the suggestion that protons and capsaicin might activate the same ion channels. 2. In this study we simultaneously measured fluorescence signals and whole-cell currents activated by capsaicin or protons in acutely isolated DRG neurones filled with a high concentration (1 mM) of the Ca2P indicator dye fura-2. From these measurements the fractional contribution of Ca2P (Pf; the portion of the whole-cell current carried by Ca2+) to capsaicin-and two types of proton-induced (fast and slowly inactivating) membrane currents was determined. 3. Capsaicinand slowly inactivating proton-induced currents were accompanied by a change in fluorescence that was dependent on the presence of extracellular Ca2+. With 1 6 mm extracellular Ca2+ and at a holding potential of-80 mV Pf of capsaicin-induced currents (at pH 7'3) was 4-30 + 0-17% (mean +s.E.M.; no. of experiments, n = 16) and of slowly inactivating proton-induced currents (at pH 5-1) was 1 65 + 0'11 % (n = 17). Pf of fast inactivating proton-induced currents was negligible. 4. Pf of capsaicin-and slowly inactivating proton-induced currents increased with increasing extracellular Ca2+ concentration (0'5-4'8 mM). 5. Pf of both current types decreased linearly with decreasing extracellular pH by about 0 7 % per pH unit over the pH range investigated. When determined at the same extracellular pH Pf values were significantly different for the two current types at all pH values tested. 6. In summary, our results provide evidence that capsaicin and protons activate ion channels which are markedly permeable to Ca2+. The fractional contribution of Ca2+, however, was significantly different for capsaicin-and slowly inactivating proton-induced currents. This strongly suggests that the two stimuli activate different populations of ion channels and supports the possibility that Ca2P influx through these channels may be important for Ca2+dependent sensitization of primary nociceptive neurones. Capsaicin (8-methyl-N-vanillyl-6-nonenamide), a pungent Handwerker, 1990). Because of its specificity capsaicin has tasting ingredient of hot peppers, has long been known as a become a valuable tool for the identification of those dorsal potent algogen (for reviews see Holzer, 1991; Kress & Reeh, root ganglion (DRG) neurones from which polymodal 1996). Short exposure to capsaicin leads to selective nociceptive C fibres originate (for review see Holzer, 1991). excitation and pronounced sensitization of primary In these DRG neurones, which we hereafter refer to as nociceptive afferents (Culp, Ochoa, Cline & Dotson, 1989; 'nociceptive DRG neurones', capsaicin elicits a slowly Simone & Ochoa, 1991), whereas prolonged exposure causes inactivating cation current. Single channel activity desensitization to nociceptive stimuli (e.g. Maggi & Meli, underlying this current has been recorded in attached and 1988) and a specific degeneration of small diameter nerve excised patches of rat DRG neurones (Oh, Hwang & Kim, fibres and neurones (Szolcsanyi, 1987; Lang, Novak & 1996) suggesting that capsaicin probably activates the
A rapid capsaicin-activated current in rat trigeminal ganglion neurons
Proceedings of the National Academy of Sciences, 1994
A subpopulation of pain fibers are activated by capsaicin, the ingredient in red peppers that produces a burning sensation when eaten or placed on skin. Previous studies on dorsal root ganglion neurons indicated that capsaicin activates sensory nerves via a single slowly activating and inactivating inward current. In rat trigeminal neurons, we identified a second capsaicin-activated inward current. This current can be distinguished from the slow one in that it rapidly activates and inactivates, requires Ca2+ for activation, and is insensitive to the potent capsaicin agonist resiniferatoxin. The rapid current, like the slower one, is inhibited by ruthenium red and capsazepine. The two capsaicin-activated inward currents share many similarities with the two inward currents activated by lowering the pH to 6.0. These similarities include kinetics, reversal potentials, responses to Ca2+, and inhibition by ruthenium red and capsazepine. These results suggest that acidic stimuli may be an endogenous activator of capsaicingated currents and therefore may rationalize why pain is produced when the plasma acidity is increased, as occurs during ischemia and inflammation.
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1997
Capsaicin (Cap) is a pungent extract of the Capsicum pepper family, which activates nociceptive primary sensory neurons. Inward current and membrane potential responses of cultured neonatal rat dorsal root ganglion neurons to capsaicin were examined using whole-cell and perforated patch recording methods. The responses exhibited strong desensitization operationally classified as acute (diminished response during constant Cap exposure) and tachyphylaxis (diminished response to successive applications of Cap). Both acute desensitization and tachyphylaxis were greatly diminished by reductions in external Ca2+ concentration. Furthermore, chelation of intracellular Ca2+ by addition of either EGTA or bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid to the patch pipette attenuated both forms of desensitization even in normal Ca2+. Release of intracellular Ca2+ by caffeine triggered acute desensitization in the absence of extracellular Ca2+, and barium was found to effectively ...
Brain Research, 2008
Hyperalgesia and allodynia occur as a consequence of peripheral and central sensitization that follows sustained nociceptive activation. The cellular alterations associated to this state of nociceptive network hyperexcitability represent a form of neuronal plasticity, but they are not well understood because of its complexity in situ. In this study, after treating primary spinal neuron cultures with capsaicin (0.5-1 μM) for 48 h fluorimetric recordings were performed. The activation of TRPV1 receptors with capsaicin (0.5-1.0 μM) increased the frequency of calcium transients (0.03± 0.002 Hz vs. 0.05± 0.006 Hz, P b 0.05), mediated by AMPAergic transmission, as well as the percent of neurons with activity (37 ± 3% vs. 65± 4%, P b 0.05). The effect of capsaicin was long lasting and the neurons were found to be hyperfunctional and with increased levels of phosphorylated CREB (cAMP responsive element binding) even after 72 h of treatment with capsaicin (32 ± 5% vs. 52 ± 5%). The effect of capsaicin was blocked by capsazepine (1 μM), TTX (100 nM) and KN-62 (1 μM), but not by K252a (200 nM) or PD98059 (50 μM) indicating the involvement of TRPV1. The results suggest the participation of Ca 2+ , CaMKII and CREB on the prolonged enhancement of excitability following chronic exposure to capsaicin. Thus, it is likely that chronic TRPV1 activation is capable of inducing prolonged increases in neurotransmission mediated by glutamatergic receptors.
Biochemical and Biophysical Research Communications - BIOCHEM BIOPHYS RES COMMUN, 2001
2؉ -free solution. Capsazepine, an antagonist of capsaicin receptor, completely blocked the capsaicin-induced [Ca 2؉ ] i transient. Caffeine completely abolished capsaicin-induced [Ca 2؉ ] i transient. Dantrolene sodium and ruthenium red, antagonists of the ryanodine receptor, blocked the effect of capsaicin on [Ca 2؉ ] i . However, capsaicin-induced [Ca 2؉ ] i transient was not affected by 2-APB, a
Neuroscience, 1993
The effects of caps&in cytosolic Ca2+ concentration (ICa*+l) were measured in individual dorsal root ganglion neurons of the rat in culture. Capsaicin produced a rapid concentration-dependent (xc+,, value of 72 nM) increase in [Ca*+], which was entirely dependent on Ca*+ entry. Exposure of the neurons to a high concentration of capsaicin resulted in desensitization, but only in the presence of external Ca2+. Raising [Ca2+li with a depolarizing concentration of potassium or the Caz+ ionophore ionomycin did not reduce the response to a subsequent application of capsaicin. Capsaicin did not induce desensitization in Ca2+-free medium even if [Ca2+li was simultaneously raised with a combination of ionomycin plus carbonyl cyanide m-chlorophenyl-hydrazone. Okadaic acid, a known inhibitor of protein phosphatases 1 and 2A, caused a transient dose-dependent (ec, value, 100 nM) rise in [Ca2+],, but had no effect on either the responsiveness to capsaicin or eapsaicin induced desensitization. The cap&in antagonist capsaxepine blocked the increase in [Ca*+l, evoked by capsaicin and prevented desensitization. These results suggest that desensitization requires the presence of extracellular Ca2+, cannot be mimicked by raising the concentration of [Ca'+], and may involve Ca2+ entry through activated capsaicin-operated ion chamrels.
Low pH facilitates capsaicin responses in isolated sensory neurons of the rat
Neuroscience Letters, 1996
The effects of capsaicin (CAPS; 30 nM, 300 nM, 3/~M) and acidic solutions (pH 6.6, 6.1, 5.6, 5.1) were studied in dorsal root ganglion (DRG) neurons from adult rats in short term culture using the whole cell patch-clamp technique and a system for fast drug application. At -60 mV holding potential, both CAPS 30 nM and 300 nM for 10 s did not induce a significant membrane current in pH 7.3. The first response to 3/zM CAPS at pH 7.3 yielded an inward current of 898 _+ 517 pA and with pH 6.1 the sustained protoninduced current was 365 -+ 153 pA. A more than additive current increase was observed when both agents were applied together even at subthreshold concentrations of CAPS or protons. Similar results were obtained at positive holding potential. Facilitation was also observed when extracellular pH 6.1 solution was applied immediately after discontinuation of 3/zM CAPS application but not when CAPS followed the application of pH 6.1 solution (n = 8). The proton-induced current as well as the CAPS-pH response both increased with proton concentration and showed the same short relaxation time relative to the CAPS response. The facilitation saturated near pH 5.6, and was present in repeated trials when responses to CAPS were markedly decreased due to tachyphylaxis. It is suggested that protonation of CAPS gated ion channels increases their open probability or conductance and modulates their kinetics.
Exposure to calcium-free medium protects sensory fibers by capsaicin desensitization
Neuroscience Letters, 1987
Capsaicin (1 pM) produces a tetrodotoxin-resistant contraction of the rat isolated urinary bladder ascribable to neuropeptide release from sensory nerves. A second application of capsaicin (1 10 itM) up to 5 h from the first one was ineffective, indicating complete desensitization. However, if the first exposure to capsaicin was made after a prolonged incubation in a Ca-free medium containing EDTA (0.1 raM), a second application of capsaicin (1/zM) was still able to induce a contraction, thus indicating protection from desensitization. Capsaicin exerts a selective excitatory (depolarizing) action on certain sensory nerves which determines activation of afferent discharge and also a depolarizationcoupled secretion of stored transmitters from peripheral terminals (see ref. 11 for a review). The sensory receptor itself seems a main target for the stimulatory action of capsaicin [7, 11]. The depolarization-coupled transmitter secretion [3, 11] determines a variety of visceromotor responses to capsaicin in isolated organs, such as the rat urinary bladder [5, 8, 10]. The depolarizing action of capsaicin on sensory nerve terminals is tetrodotoxin (TTX)-resistant, e.g. does not require activation of fast Na + channels, but the neurogenic nature of these responses can be easily demonstrated following chronic extrinsic denervation which depletes bladder content of sensory neuropeptides [5, 6, 8, 10]. Although the ionic basis of depolarization of sensory terminals is still largely unexplored, some evidence indicates that an increase in conductance to calcium ions (Ca) may be involved [I I]. Within a short time from the end of the excitatory effect of capsaicin the nerve terminals become unexcitable to both capsaicin and natural stimuli [4, 7]. In this communication we present evidence that exposure to a Ca-free medium protects the sensory terminals of the rat urinary bladder from the desensitizing action of capsaicin.