A disrupter of actin microfilaments impairs sulfonylurea-inhibitory gating of cardiac K-ATP channels

The efficacy with which sulfonylurea drugs inhibit cardiac ATP-sensitive K+ (K-ATP) channels is reduced during metabolic compromise and cellular contracture, Disruption of the actin microfilament artwork? which occurs under similar conditions, reduces tl-io sensitivity of the channel toward intracellular ATP. To investigate whether a disrupter of actin microfilaments could also affect the responsiveness of the K-ATP channel to sulfonylurea drugs, single-channel currents were measured in the inside-out configuration of excised patches from guinea pig ventricular myocytes. Treatment of the internal side of patches with deoxyribonuclease (DNase) I (100 mu g/ml), which forms complexes with G actin and prevents actin filament formation, antagonized sulfonylurea-induced inhibition of K-ATP channels that was coupled with a loss of sensitivity to ATP. The apparent dissociation constant and Hill coefficient for the inhibitory effect of glyburide, a prototype sulfonylurea, on K-ATP-channel opening were, respectively, 0.13 mu M and 0.95 before and 2.7 mu M and 0.98 after DNase treatment. DNase did not alter intraburst kinetic properties of the channel. When DNase was denatured or coincubated with purified actin (200 mu g/ml), it no longer decreased glyburide-induced channel inhibition. This suggests that sulfonylurea-inhibitory gating of cardiac K-ATP channels may also be regulated. through a mechanism involving subsarcolemmal actin microfilament networks.