title: An outwardly rectifying K+ current active near resting potential in human retinal pigment epithelial cells.
abstract: 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.
authors.affiliation: Department of Ophthalmology, University of Michigan, Ann Arbor 48105, USA.
authors.forename: B A
authors.initials: BA
authors.lastname: Hughes
authors.forename: M
authors.initials: M
authors.lastname: Takahira
authors.forename: Y
authors.initials: Y
authors.lastname: Segawa
mesh_terms: D000328:Adult; D000368:Aged; D001464:Barium / Q000494:pharmacology; D004553:Electric Conductivity; D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D008875:Middle Aged; D010857:Pigment Epithelium of Eye / Q000166:cytology / Q000502:physiology*; D011188:Potassium / Q000502:physiology*; D026902:Potassium Channel Blockers; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
chemical_list: D026902:Potassium Channel Blockers; D013757:Tetraethylammonium Compounds; D001464:Barium; D019789:Tetraethylammonium; D011188:Potassium