An outwardly rectifying k+ current active near the resting
potential in human retinal pigment epithelial cells.
Hughes, Bret A., Masayuki Takahira, and Yasunori Segawa.
Departments of Ophthalmology and Physiology, University of
Michigan, Ann Arbor, MI 48105
APStracts 2:0084C, 1995.
Currents in freshly dissociated adult human retinal pigment epithelial
(RPE) cells were studied using the perforated patch-clamp technique.
The zero-current potential (V0) averaged -48.9 +/- 7.7 mV (n=50).
Depolarizing voltage pulses from -70 mV evoked an outward current
that activated with first order kinetics and which did not inactivate
during prolonged depolarizations. Repolarizing the membrane potential
produced tail currents that reversed near EK, indicating that the
sustained outward current was carried mainly by K+. The outwardly
rectifying K+ conductance (gK) had an activation threshold voltage
near -60 mV and was half-maximal at -37 mV. Approximately 25% of gK
was active at the average V0. The K+ current was nearly completely
blocked by 2 mM Ba2+ but was relatively insensitive to 20 mM
tetraethylammonium. The kinetics, voltage dependence, and blocker
sensitivity of this current clearly distinguish it from delayed
rectifier K+ currents previously identified in RPE cells. We conclude
that the sustained outward K+ current may help establish the resting
potential of the apical and/or basolateral membranes and may also
participate in K+ transport across the RPE.
Received 31 October 1994; accepted in final form 9 January 9
1995.
APS Manuscript Number C646-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 28 February 1995.