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Abstract
The endocochlear DC potential (EP) is generated by the stria vascularis, and essential
for the normal function of hair cells. Intermediate cells are melanocytes in the stria
vascularis. To examine the contribution of the membrane potential of intermediate
cells (E(m)) to the EP, a comparison was made between the effects of K(+) channel
blockers on the E(m) and those on the EP. The E(m) of dissociated guinea pig intermediate
cells was measured in the zero-current clamp mode of the whole-cell patch clamp configuration.
The E(m) changed by 55.1 mV per 10-fold changes in extracellular K(+) concentration.
Ba(2+), Cs(+), and quinine depressed the E(m) in a dose-dependent manner, whereas
tetraethylammonium at 30 mM and 4-aminopyridine at 10 mM had no effect. The reduction
of the E(m) by Ba(2+) and Cs(+) was enhanced by lowering the extracellular K(+) concentration
from 3.6 mM to 1.2 mM. To examine the effect of the K(+) channel blockers on the EP,
the EP of guinea pigs was maintained by vascular perfusion, and K(+) channel blockers
were administered to the artificial blood. Ba(2+), Cs(+) and quinine depressed the
EP in a dose-dependent manner, whereas tetraethylammonium at 30 mM and 4-aminopyridine
at 10 mM did not change the EP. A 10-fold increase in the K(+) concentration in the
artificial blood caused a minor decrease in the EP of only 10.6 mV. The changes in
the EP were similar to those seen in the E(m) obtained at the lower extracellular
K(+) concentration of 1.2 mM. On the basis of these results, we propose that the EP
is critically dependent on the voltage jump across the plasma membrane of intermediate
cells, and that K(+) concentration in the intercellular space in the stria vascularis
may be actively controlled at a concentration lower than the plasma level.