Activation of Ca2+-dependent K+ channels by cyanide in guinea pig adrenal chromaffin cells

Abstract

The effects of cyanide (CN) on whole cell current measured with the perforated-patch method were studied in adrenal medullary cells. Application of CN produced initially inward and then outward currents at −52 mV or more negative. As the membrane potential was hyperpolarized, amplitude and latency of the outward current ( I o) by CN became small and long, respectively. A decrease in the external Na+ concentration did not affect the latency for CN-induced I o but enhanced the amplitude markedly. The CN I o reversed polarity at −85 mV, close to the Nernst potential for K+, and was suppressed by the K+ channel blockers curare and apamin but not by glibenclamide, suggesting that I o is due to the activation of Ca2+-dependent K+ channels. Consistent with this notion, the Ca2+-mobilizing agents, muscarine and caffeine, also produced I o. Exposure to CN in a Ca2+-deficient medium for 4 min abolished caffeine- or muscarine-induced I o without development of I o, and addition of Ca2+ to the CN-containing solution induced I o. We conclude that exposure to CN produces Ca2+-dependent K+ currents in an external Ca2+-dependent manner, probably via facilitation of Ca2+ influx.