ATP-dependent potassium channels in the cardiac cell.

Patch-clamp techniques were used to study the ATP-dependent K+ channel in single ventricular myocytes from guinea pig hearts. During long lasting whole-cell recordings an increase of a time-independent K+ outward current could be observed. This outward current could be inhibited by the intracellular application of ATP (3-20 mM), but not by the Ca2+-chelator EGTA (20 mM). The blocking effect of ATP was also observed in single-channel experiments. The hypoglycaemic sulphonylurea tolbutamide specifically inhibited the ATP-dependent K+ current in whole-cell recordings, inside-out and outside-out patches (IC50 = 0.4 mM).