Anion dependence of electrical effects of bicarbonate and sodium on cultured bovine corneal endothelial cells

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Abstract
Using intracellular microelectrode technique, the effect of anion substitution on the voltage responses to extracellular bicarbonate and sodium was explored in cultured bovine corneal endothelial cells. The overall amplitude of voltage changes induced by periodic changes of [HCO 3 − ]0 (depolarization upon removal of HCO 3 − and hyperpolarization upon readdition) was reduced when Cl− was replaced by organic anions (cyclamate, methylsulfate, benzenesulfonate) or by SO 4 2− , and to a lesser extent by substitution with Br−. There was a similar effect of anion substitution on the response to changes of [Na+]0. In both cases, in the absence of Cl, the voltage V returned at a slower rate to baseline levels after it had been transiently changed by either an imposed Na- or HCO3-gradient, indicating a slower dissipation of these gradients. The direct response of V to these imposed gradients was affected only to a minor degree. Replacement of Cl− by SO 4 2− or organic anions led to a slow, reversible depolarization of the cell, while substitution with Br− had only a slight effect. The effect of anion substitution on the voltage responses to HCO 3 − or Na+ could not be mimicked by a depolarization induced by Ba2+ (1 mM). Furosemide (10−3 M) led to a slight reduction of the voltage responses to HCO 3 − , but could not suppress the effect of anion substitution on these reactions. It could neither suppress the depolarization induced by anion substitution and had no effect on steady-state PD. It is suggested, that cultured bovine corneal endothelial cells, in addition to a previously demonstrated electrogenic HCO 3 − −Na+-cotransport, which is probably not dependent on Cl, possess an electroneutral mechanism for HCO 3 − and/or Na+-movement, which depends on Cl. No evidence for a Cl-conductance could be obtained.