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

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.