Ca(2+)-activated nonselective cation channel in apical membrane of vestibular dark cells.
Patch-clamp recordings were made on cell-attached and excised apical membrane from dark cells of the semicircular canal of the gerbil. These cells are thought to secrete K+ and absorb Na+ from the luminal fluid (endolymph). Single-channel events were identified as being equally conductive (27.6 +/- 0.4 pS; n = 48) for K+, Na+, Rb+, Li+, and Cs+ and 1.4 times more permeable to NH4+ but not permeable to Cl-, Ca2+, Ba2+, nor to N-methyl-D-glucamine. The channels displayed linear current-voltage relations that passed nearly through the origin (intercept: -2.6 +/- 0.5 mV; n = 48) when conductive monovalent cations were present on both sides of the membrane in equal concentrations. Channel activity required the presence of Ca2+ at the cytosolic face; there was no activity at less than or equal to 10(-7) M Ca2+ and full activity at greater than or equal to 10(-5) M Ca2+. Cell-attached recordings had a mean reversal voltage of -36.4 +/- 7.9 mV (n = 7), which was interpreted to reflect the intracellular potential of dark cells under the present conditions. We have identified a nonselective cation channel in the apical membrane of vestibular dark cells that might participate in K+ secretion or Na+ absorption under stimulated conditions, but the density appears to be insufficient to fully account for the transepithelial K+ flux.
Marcus
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DC
Biophysics Laboratory, Boys Town National Research Hospital, Omaha, Nebraska 68131.
Takeuchi
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Wangemann
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D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002414:Cations, Monovalent / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D005849:Gerbillinae; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects / Q000502:physiology*; D008433:Mathematics; D008564:Membrane Potentials; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism; D012665:Semicircular Canals / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D012964:Sodium / Q000378:metabolism
D002414:Cations, Monovalent; D007473:Ion Channels; D012964:Sodium; D011188:Potassium; D002118:Calcium