AJP - Cell Physiology, Vol 262, Issue 6 C1430-C1436, Copyright © 1992 by American Physiological Society
Maxi K+ channel in apical membrane of vestibular dark cells
S. Takeuchi, D. C. Marcus and P. Wangemann
Biophysics Laboratory, Boys Town National Research Hospital, Omaha, Nebraska 68131.
Recordings were made on excised apical membrane patches from vestibular
dark cells from the semicircular canal of gerbils to determine if ion
channels could be involved in the process of K+ secretion. Both
nonselective cation channels [Am. J. Physiol. 262 (Cell Physiol. 31):
C1430-C1436, 1992] and K(+)-selective channels were found. The K+ channels
occurred in only 0.7% of the patches. In symmetrical 145 mM KCl solutions,
the current-voltage (I-V) relation of the K(+)-selective channel was
linear, indicating the absence of rectification, and the conductance was
240 +/- 8 pS (n = 8). The Goldman-Hodgkin-Katz equation for current carried
solely by K+ could be fitted to the I-V relation in asymmetrical K+ and Na+
solutions and yielded a K+ permeability of 5.78 x 10(-13) cm3/s (n = 12).
The channel was shown to be impermeable to Li+, NH4+, N-methyl-D-glucamine,
and Cl-. Channel activity increased with depolarization and with increasing
free [Ca2+]; for voltages between +40 and -60 mV, the strongest regulation
occurred in the range 10(-6) to 10(-5) M Ca2+. Tetraethylammonium (2 x
10(-2) M) had from the cytosolic side no effect on the open probability
(Po) but completely inhibited activity from the extracellular side. Po was
reduced by Ba2+ (5 x 10(-3) M), verapamil (10(-4) M), quinine (10(-4) M),
and quinidine (10(-4) and 10(-3) M), while lidocaine (5 x 10(-3) M) had no
measurable effect on Po but decreased the amplitude. Rb+ and Cs+ were
either poorly permeable or partially blocked the channel in a
voltage-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)
