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Am J Physiol Cell Physiol 269: C179-C187, 1995;
0363-6143/95 $5.00
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AJP - Cell Physiology, Vol 269, Issue 1 C179-C187, Copyright © 1995 by American Physiological Society

ARTICLES

An outwardly rectifying K+ current active near resting potential in human retinal pigment epithelial cells

B. A. Hughes, M. Takahira and Y. Segawa
Department of Ophthalmology, University of Michigan, Ann Arbor 48105, USA.

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 that did not inactivate during prolonged depolarizations. Repolarizing the membrane potential produced tail currents that reversed near the K+ equilibrium potential, 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.


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