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Department of Physiology, Kochi Medical School, Nankoku 783-8505, Japan
A voltage-dependent outward
K+
(KV) current in the intermediate
cell (melanocyte) of the cochlear stria vascularis was studied using
the whole cell patch-clamp technique. The
KV current had an activation
threshold voltage of approximately
80 mV, and 50% activation
was observed at
42.6 mV. The time courses of activation and
inactivation were well fitted by two exponential functions: the time
constants at 0 mV were 7.9 and 58.8 ms for activation and 0.6 and 4.3 s
for inactivation. The half-maximal activation time was 13.8 ms at 0 mV.
Inactivation of the current was incomplete even after a prolonged
depolarization of 10 s. This current was independent of intracellular
Ca2+. Quinine, verapamil,
Ba2+, and tetraethylammonium
inhibited the current in a dose-dependent manner, but 4-aminopyridine
was ineffective at 50 mM. We conclude that the
KV conductance in the intermediate
cell may stabilize the membrane potential, which is thought to be
closely related to the endocochlear potential, and may provide an
additional route for K+ secretion
into the intercellular space.
patch clamp; melanocyte; endocochlear potential
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