AJP - Cell Physiology, Vol 262, Issue 6 C1423-C1429, Copyright © 1992 by American Physiological Society
Ca(2+)-activated nonselective cation channel in apical membrane of vestibular dark cells
D. C. Marcus, S. Takeuchi and P. Wangemann
Biophysics Laboratory, Boys Town National Research Hospital, Omaha, Nebraska 68131.
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.
