K+-conductance and electrogenic Na+/K+ transport of cultured bovine pigmented ciliary epithelium

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Abstract
Using intracellular microelectrode technique, we investigated the changes in membrane voltage (V) of cultured bovine pigmented ciliary epithelial cells induced by different extracellular solutions. (1)V in 213 cells under steady-state conditions averaged −46.1±0.6 mV (sem). (2) Increasing extracellular K+ concentration ([K+] o ) depolarizedV. Addition of Ba2+ could diminish this response. (3) Depolarization on doubling [K+] o was increased at higher [K+] o (or low voltage). (4) Removing extracellular Ca2+ decreasedV and reduced theV amplitude on increasing [K+] o . (5)V was pH sensitive. Extra-and intracellular acidification depolarizedV; alkalinization induced a hyperpolarization.V responses to high [K+] o were reduced at acidic extracellular pH. (6) Removing K o + depolarized, K o + readdition after K+ depletion transiently hyperpolarizedV. These responses were insensitive to Ba2+ but were abolished in the presence of ouabain or in Na+-free medium. (7) Na+ readdition after Na+ depletion transiently hyperpolarizedV. This reaction was markedly reduced in the presence of ouabain or in K+-free solution but unchanged by Ba2+. It is concluded that in cultured bovine pigmented ciliary epithelial cells K+ conductance depends on Ca2+, pH and [K+] o (or voltage). An electrogenic Na+/K+-transport is present, which is stimulated during recovery from K+ or Na+ depletion. This transport is inhibited by ouabain and in K+-or Na+-free medium.