Outward k+ current in the epithelial cells isolated from the
intermediate portion of the endolymphatic sac in guinea pigs.
Wu, Dazheng, and Nozomu Mori.
Department of Otolaryngology, Kagawa Medical School, Japan
APStracts 3:0201C, 1996.
Ion currents in epithelial cells isolated from the intermediate
portion of endolymphatic sac (ES) in guinea pigs were investigated
using the whole-cell patch-clamp technique. The depolarizing voltage
steps from a holding potential of - 60 mV induced a time- and
voltage-dependent outward current, which is comparable to that of
delayed rectifying K+ currents. The average resting membrane
potential in the current-clamp mode was - 54.7+/- 1.3 mV ( n = 34 ),
which was similar to the value of zero current potential (- 53.9 +/-
1.7 mV; n = 16 ) obtained from current / voltage ( I/V )
relationships of outward currents in voltage-clamp mode. The I/V
relationship of the tail current exhibited a reversal potential of -
78.1 +/- 0.9 mV (n=19) in standard external solution. The reversal
potential of the outward current was linearly related to the
logarithm of extracellular K+ concentrations. The slope was 48 mV per
ten-fold change in extracellular K+ concentrations. The time constant
of K+ current activation and K+ tail current deactivation were
voltage-dependent. The activation and inactivation of K+ current
exhibited a sigmoid relationship to voltage. The half-maximal
activation voltage and slope factor were - 21 mV and 11 mV ( n = 8 ),
respectively. The half-maximal inactivation voltage and slope factor
were - 45 mV and 13 mV ( n = 7 ), respectively. The K+ current was
blocked by externally applied 1 mM 4-AP and 20 mM TEA. The
sensitivity of the current to 4-AP was higher than that to TEA.
Elimination of external Ca2+ or buffering internal Ca2+ with EGTA
failed to significantly change the current, suggesting that the K+
current may be Ca2+ -independent. The results show that the
epithelial cells in the intermediate portion of the ES possess a
delayed rectifier K+ current, which may play important roles in K+
transport and K+ homeostasis in the ES.
Received 30 October 1995; accepted in final form 6 June 1996.
APS Manuscript Number C656-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 4 July 96