ATP-sensitive K+ channels in heart muscle cells first open and subsequently close at maintained anoxia.

In ventricular myocardial cells of the guinea pig and the mouse, anoxia caused after a mean latency of 439 +/- 141 s and 129 +/- 23 s (mean +/- S.E.M.), respectively, a large current through KATP-channels. This current disappeared within several seconds when reoxygenating the cells but decayed also completely at maintained anoxia. The kinetics of the latter process, however, were much slower and obeyed an approximately monoexponential time course with time constants in the range of 30 s. The results suggest that in the ischaemic myocardium KATP-channels contribute only to the initial phase of extracellular K+ accumulation.