Mechanism of the effect of cyanide on cell membrane potentials in Necturus gall‐bladder epithelium.

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Abstract
Addition of sodium cyanide to the mucosal or the serosal medium bathing the isolated gall-bladder of N. maculosus causes hyperpolarization of both apical and basolateral membrane of the epithelial cells. The effect of cyanide is practically immediate, reversible (if exposure is brief) and long-lasting (> 30 min). The hyperpolarization is accompanied by reduction of the equivalent resistance of the cell membranes, as shown by cable analysis and input resistance measurements, and increase of the K selectivity of both cell membranes, as evidence by the effects of external substitutions of K for Na on cell membrane potentials. The cyanide-induced hyperpolarization is caused mainly or exclusively by an increase of the K permeability of the cell membranes. Addition of the Ca ionophore A23187 (5 .mu.M) to the mucosal medium in the presence of 1 mM-Ca caused similar effects to those produced by cyanide. After either cyanide or A23187, addition of the other agent did not cause further membrane potential changes. Quinine (100 .mu.M, mucosal medium) reduced the K permeability of the apical membrane both under control conditions and during exposure to cyanide. Probably, the cyanide-induced increase of the K permeability of the cell membrane is mediated by an elevation of intracellular Ca2+ activity, attributable to release from mitochondrial sources.

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