Differential sensitivity of cardiac K+(ATP) channels to guanine nucleotides--evidence for a heterogeneous channel population.

In cell-free patches from cultured neonatal rat cardiocytes, the cytosolic presence of GTP-gamma-S (100 mumol/l) or GDP-beta-S (100 mumol/l) activated K+(ATP) channels. GTP-gamma-S required cytosolic Mg++, suggesting that an activated G-protein causes the increase in open probability. The great variations of the channel response to GTP-gamma-S and GDP-beta-S indicates that cardiac K+(ATP) channels represent a heterogeneous family.