Slowly activating voltage-dependent K+ conductance is apical pathway for K+ secretion in vestibular dark cells.
Dark cell epithelium secretes K+ into the lumen of the vestibular labyrinth by a previously unidentified apical transport mechanism. Previous single-channel patch-clamp studies demonstrated nonselective cation channels and maxi-K+ channels in the apical membrane, but in too low a density to account for transepithelial K+ transport. In this report, we demonstrated with the cell-attached macro-patch-clamp technique an outward apical membrane current at 0-mV pipette voltage, which was stimulated by elevating bath K+ concentration from 3.6 to 25 mM and inhibited by 10 microM bumetanide, similar to their known effects on transepithelial short-circuit current and K+ secretion. Furthermore, the patch current was activated over several seconds by a sustained depolarization and deactivated over several hundred milliseconds by a hyperpolarization. Current-voltage relationships from tail currents were obtained with either NaCl or KCl in the pipette. Depolarization from -40 to +40 mV led to an increased conductance by a factor of 7.3 +/- 1.7 (n = 7) and 19.2 +/- 7.6 (n = 6) for NaCl and KCl, respectively, and to a reversal voltage near the presumed equilibrium potential for K+. The results demonstrate that dark cell K+ secretion occurs via K(+)-selective channels with characteristics similar to those associated with the IsK protein.
Marcus
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Biophysics Laboratory, Boys Town National Research Hospital, Omaha, Nebraska 68131.
Shen
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D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D004553:Electric Conductivity; D004594:Electrophysiology / Q000379:methods; D005849:Gerbillinae; D011188:Potassium / Q000378:metabolism / Q000502:physiology*; D011189:Potassium Chloride / Q000494:pharmacology; D012965:Sodium Chloride / Q000494:pharmacology; D012996:Solutions; D013997:Time Factors; D014722:Vestibule, Labyrinth / Q000166:cytology / Q000378:metabolism / Q000502:physiology*
D012996:Solutions; D012965:Sodium Chloride; D011189:Potassium Chloride; D011188:Potassium