Cyanide suppression of inwardly rectifying K+ channels in guinea pig chromaffin cells involves dephosphorylation

Treatment of chromaffin cells with cyanide induced a gradual decrease in an inwardly rectifying K+ current (IIR), and washout of the mitochondrial inhibitor resulted in a rapid recovery of IIR. This diminution of IIR was reversed in a time-dependent manner by infusion of ATP or UTP, but not by that of GTP, ITP, or CTP. The restoration by ATP was not altered by addition to the pipette solution of 50 microM fluorescein 5-isothiocyanate, an inhibitor of various ATPases. A similar recovery of IIR occurred with injection of adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S), but not of 5'-adenylylimidodiphosphate or alpha,beta-methyleneadenosine 5'-triphosphate. The ATP gamma S effect was biphasic, resulting in first a run-up of the current in ATP-depleted cells followed by a rundown of the current. This rundown was almost abolished by addition of guanosine 5'-O-(2-thiodiphosphate) to the ATP gamma S solution, suggesting the involvement of a G protein. Bath application of the protein kinase inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine at 100 microM, but not N-(2-[methylamino]-ethyl)-5-isoquinolinesulfonamide, induced a reversible inhibition of IIR in the presence of pipette ATP, and the inhibition was diminished by 1 microM calyculin A, a phosphatase inhibitor. Bath application of 1 microM phorbol 12,13-dibutyrate did not affect IIR. It is concluded that cyanide suppresses inward rectifier K+ channel activity via dephosphorylation and that protein kinase C, adenosine 3',5'-cyclic monophosphate-dependent kinase, or guanosine 3',5'-cyclic monophosphate-dependent kinase is not involved in modulation of the channel.