Current-voltage relations of Cs+-inhibited K+ currents through the apical membrane of frog skin (original) (raw)
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Effect of mucosal H+ and chemical modification on transcellular K+ current in frog skin
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1990
A transcellular K + current (I K) was established across the skin of the frog Rana temporaria, whose apical K ÷ permeability had been previously stimulated by exposure to K +-Hch media. Short-term (< 15 s) mucosal pH-titration of I K indicated two titrated groups (A and B), with apparent pK A of 6 and pK B of 3. The height of the titration steps, A and B, varied from skin to skin. Intracellular (i) H +-sensitive microelectrode studies on Rana esculenta skin (which lacks apical Pa) were conducted in order to assess possible changes in pH i and basolateral K + conductance as a consequence of the rise in mucosal [H + ]. Cell pH decreased only at mucosal pH lower than 5.4 which caused a drop in hasolateral K + conductance as estimated from I-V records of the serosal membranes. These effects were much too slow to account for the fast mucosal pH effects on I K (Rana temporaria). Thus, we conclude that the two-step titration curves reflect solely the interaction of external H + with the mucosal side of apical membrane K + channels. Exposure to the SH-reagent PCMB, and to the carboxy-modifying EEDQ markedly reduced total IK at neutral pH; however, PCMB seemed to preferentially affect titration step B while EEDQ virtually eliminated step A. When the saturating I K kinetics were studied at different mucosal pH, protons showed a 'mixed' type inhibition of K + current in the range of titration step A; at pH values less than 5, protons blocked I K by competition with K + ions. These results are compatible with the presence of two K + channel populations in the apical membrane which are discernible by their different interactions with external protons and chemical modifiers.
The interaction of “K+-like” cations with the apical K+ channel in frog skin
The Journal of Membrane Biology, 1983
The apparent permeability of the apical K + channel in the abdominal skin of the frog (Rana temporaria) for different monovalent cations was tested by comparing the shortcircuit current (SCC) obtained after imposition of serosally directed ionic concentration gradients. Furthermore, the SCC was subjected to noise analysis. Of various cations tested, only the "K+-like '' ions NH~, Rb + and T1 +, besides K +, were found to permeate the apical K + channel, as reflected by SCC-and fluctuation analysis : (i) The SCC could be depressed by addition of the K +-channel blocker Ba 2 + to the mucosal solution. (i/) With the K+-like ions (Ringer's concentration), a spontaneous Lorentzian noise was observed. Plateau values were similar for K + and T1 +, and smaller for NH 2 and Rb +. The corner frequencies clearly increased in the order K § < NH~-< T1 + ~ Rb +. The SCC dose-response relationships revealed a Michaelis-Menten-type current saturation only for pure K +-or T1 +-Ringer's solutions as mucosal medium, whereas a more complicated SCC behavior was seen with Rb + and especially, NH~-. For K +-T1 + mixtures an anomalous mole-fraction relationship was observed: At low [TI+]/[K +] ratios, T1 + ions appeared to inhibit competitively the K + current while, at high [TI+]/ [K +] ratios, T1 + seemed to be a permeant cation. This feature was also detected in the noise analysis of K+-T1 + mixtures. Long-term exposure to mucosal T1 + resulted in an irreversible deterioration of the tissue. The SCC depression by Ba 2 + was of a simple saturation-type characteristic with, however, different half-maximal doses (NH~-<K+< Rb+). Ba 2+ induced a "blocker noise" in presence of all permeant cations with corner frequencies that depended on the Ba 2 + concentration. A linear increase of the corner frequencies of the Ba 2 +-induced noise with increasing Ba z+ concentration was seen for NH2, Rb + and K +. With the assumption of a pseudo two-state model for the Ba 2 + blockade the on-and off-rate constants for the Ba z + interaction with the NH2/Rb+/K + channel were calculated and showed marked differences, dependent on the nature of the permeant ion. The specific problems with T1 + prevented such an analysis but SCC-and noise data indicated a comparably poor efficiency of Ba 2 § as Tl+-current inhibitor. We attempted a qualitative analysis of our results in terms of a "twosites, three-barriers" model of the apical K + channel in frog skin.
Biochemical and Biophysical Research Communications, 2001
The rat primary cultured-airway monolayer has been an excellent model for deciphering the ion channel after nystatin permeabilization of its basolateral or apical membrane. Inwardly rectifying K ؉ currents were characterized across the basolateral membrane in symmetrical HCO 3 ؊-free high K ؉ Ringer's solution (125 mM) in this study. The potency of K ؉ channel inhibitors against K ؉ conductance was Ba 2؉ (IC 50 ؍ 5 M) > Cs ؉ (IC 50 ؍ 2 mM) ӷ glybenclamide (IC 50 > 5 mM) ӷ TEA (IC 50 ӷ 100 mM). The application of basolateral Cs ؉ changed K ؉ conductance into an oscillating current, and its frequency (holding voltage ؍ ؊100 mV) increased with increase in concentration of basolateral Cs ؉ (0.05-5 mM) and in degree of hyperpolarization. Addition of basolateral Cs ؉ blocked inward current strongly at ؊100 mV and hardly at all at ؊60 mV, giving a sharp curvature to the I-V relation of the IRK current. RT-PCR, Western blotting, and immunohistochemical analyses showed that Kir2.1 might be present in basolateral membrane of tracheal epithelia and plasma membrane of pulmonary alveolar cells.
Fast and slow voltage modulation of apical Cl- permeability in toad skin at high [K+]
Brazilian Journal of Medical and Biological Research, 1997
The influence of voltage on the conductance of toad skin was studied to identify the time course of the activation/deactivation dynamics of voltage-dependent Clchannels located in the apical membrane of mitochondrion-rich cells in this tissue. Positive apical voltage induced an important conductance inhibition which took a few seconds to fully develop and was instantaneously released by pulse inversion to negative voltage, indicating a short-duration memory of the inhibiting factors. Sinusoidal stimulation at 23.4 mM [Cl-] showed hysteresis in the current versus voltage curves, even at very low frequency, suggesting that the rate of voltage application was also relevant for the inhibition/releasing effect to develop. We conclude that the voltage modulation of apical Clpermeability is essentially a fast process and the apparent slow components of activation/deactivation obtained in the whole skin are a consequence of a gradual voltage build-up across the apical membrane due to voltage sharing between apical and basolateral membranes.
Inward-rectifier potassium channels in basolateral membranes of frog skin epithelium
Journal of General Physiology, 1994
Inward-rectifier K channel: using macroscopic voltage clamp and single-channel patch clamp techniques we have identified the K+ channel responsible for potassium recycling across basolateral membranes (BLM) of principal cells in intact epithelia isolated from frog skin. The spontaneously active K+ channel is an inward rectifier (Kir) and is the major component of macroscopic conductance of intact cells. The current-voltage relationship of BLM in intact cells of isolated epithelia, mounted in miniature Ussing chambers (bathed on apical and basolateral sides in normal amphibian Ringer solution), showed pronounced inward rectification which was K(+)-dependent and inhibited by Ba2+, H+, and quinidine. A 15-pS Kir channel was the only type of K(+)-selective channel found in BLM in cell-attached membrane patches bathed in physiological solutions. Although the channel behaves as an inward rectifier, it conducts outward current (K+ exit from the cell) with a very high open probability (Po =...
Inward-rectifier Potassium in Basolateral Membranes of Frog Skin Epithelium Channels
2000
Inward-rectifier K channel: using macroscopic voltage clamp and single-channel patch clamp techniques we have identified the K + channel respon- sible for potassium recycling across basolateral membranes (BLM) of principal cells in intact epithelia isolated from frog skin. The spontaneously active K + channel is an inward rectifier (Ke) and is the major component of macroscopic conductance of intact cells.
State-dependent inactivation of K+ currents in rat type II alveolar epithelial cells
The Journal of General Physiology, 1990
Inactivation of K+ channels responsible for delayed rectification in rat type II alveolar epithelial cells was studied in Ringer, 160 mM K-Ringer, and 20 mM Ca-Ringer. Inactivation is slower and less complete when the extracellular K+ concentration is increased from 4.5 to 160 mM. Inactivation is faster and more complete when the extracellular Ca2+ concentration is increased from 2 to 20 mM. Several observations suggest that inactivation is state-dependent. In each of these solutions depolarization to potentials near threshold results in slow and partial inactivation, whereas depolarization to potentials at which the K+ conductance, gK, is fully activated results in maximal inactivation, suggesting that open channels inactivate more readily than closed channels. The time constant of current inactivation during depolarizing pulses is clearly voltage-dependent only at potentials where activation is incomplete, a result consistent with coupling of inactivation to activation. Additional...
Current-voltage relationship of the basolateral membrane of a tight epithelium
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1979
The polyene antibiotic nystatin is used to reduce selectively to zero the apical membrane resistance of the rabbit descending colon, allowing the measurement of the current-voltage curve of the basolateral membrane. The I-V relationship is described by the Goldman-Hodgkin-Katz equations allowing calculation of PNa/PK, PcI/PK and PK for the basolateral membrane. Cs ÷ is found to block inward current (serosa-* mucosa) in a manner similar to that found in excitable membranes.
Journal of Cellular Physiology, 1993
The transmembrane potential (V,,,) of vascular endothelial cells (ECj is an important property that may be involved in intra-and intercellular signal transduction for various vascular functions. In this study, V,,, of intact aortic and vena caval EC from hamsters were measured using conventional microelectrodes. Vascular strips with the luminal surface upwards were suffused in a tissue chamber with Krebs solution in physiological conditions. The resting V, of aortic and vend caval EC was found to be -40 ? 1 mV (n = 55) and -43 5 1 mV (n = 15j, respectively. The V, recordings were confirmed to have originated from EC by scanning and transmission electron microscopy combined with the comparison of electrical recordings between normal and endothelium-denuded aortic strips. The input resistance varied from 10-240 MdZ, which implied the presence of electrical coupling between vascular EC. Elevating the K + level in the suffusate from 4.7 mM to 50 and 100 mM depolarized aortic EC by 19% and 29% and vena caval EC by 18% and 29%, respectively. These low percentages indicated a relatively small contribution of [ K f ] to the resting V,, of vascular EC. A positive correlation (r > 0.69) between the resting V, and the magnitude of depolarization by the high [K+], may be related to the involvement of voltage-dependent K' channels. The hyperpolarization caused by lowering both "at], and [CIp], suggested the disengagement of some electrogenic transport systems in the membrane, such as a Naf-Kf-CIp cotransporter. The transference number (t , , , ), as an index of membrane conductance for specific ions, was calculated for K' (1 5-20%), Na+ (1 6%), and CI-(9-15%), demonstrating that both Naf and CI-as well as K+ contribute (b 1993 WILEY-LISS, INC c) 1993 Wiley-Liis, Inc Klepper, 19901, membrane electrical conductivity (O'Donnell and Vargas, 1986), and electrical coupling between endothelial cells (Daut et al., 1988; Beny and Gribi, 1989), have been documented, but most of these studies were completed on cells in culture.
The Journal of physiology, 1991
1. The ionic permeability of Necturus maculosus small intestine epithelial cells was investigated using intracellular microelectrodes to measure membrane potential in intact tissue or by the single-electrode voltage-clamp technique in isolated cells. 2. The basolateral membrane of enterocytes appears to be K+ selective as demonstrated by the dependence of membrane potential and fractional serosal resistance measured in the intact epithelium on serosal K+ concentration. 3. Isolated cells had membrane potentials similar to those measured in the intact tissue. Voltage-clamp experiments in a physiological Ringer solution showed the presence of both large outward and inward currents. 4. Removal of Cl- from the bathing medium, linear subtraction or the use of a Cl- channel blocker revealed outwardly rectifying currents. The quasi-linear component was also revealed following K+ channel inhibition; it reversed near ECl, suggesting that the charge carrier was Cl-. 5. Outwardly rectifying cur...