The cardiac sarcolemmal ATP-sensitive potassium channel as a novel target for anti-arrhythmic therapy

The activation of cardiac cell membrane ATP-sensitive potassium channels during myocardial ischemia promotes potassium efflux, reductions in action potential duration, and heterogeneities in repolarization, thereby creating a substrate for re-entrant arrhythmias. Drugs that block this channel should be particularly effective anti-arrhythmic agents. Indeed, non-selective ATP-sensitive potassium channel antagonists, (e.g., glibenclamide) can prevent arrhythmias associated with myocardial ischemia. However, these non-selective antagonists have important non-cardiac actions that promote insulin release and hypoglycemia (pancreatic beta-cells), reduce coronary blood flow (vascular smooth muscle cells), prevent ischemia preconditioning (cardiac mitochondrial channels) and depress cardiac contractile function. The ATP-sensitive potassium channel consists of a pore forming inward rectifying potassium channel (Kir6.1 or Kir6.2) and a regulatory subunit (sulfonylurea receptors, SUR1, SUR2A &SUR2B). The Kir6.2/SUR2A combination appears to be preferentially expressed on cardiac cell membranes. As such, it should be possible to develop agents selective for cardiac sarcolemmal ATP-sensitive potassium channels. The novel compounds HMR 1883 (or its sodium salt HMR 1098) or HMR 1402 have been shown to block selectively the cardiac sarcolemmal ATP-sensitive potassium channels. These drugs attenuated ischemically-induced changes in cardiac electrical properties and prevented malignant arrhythmias without the untoward effects of other drugs. Since the ATP-sensitive potassium channel only becomes active as ATP levels fall, these drugs have the added advantage that they would have effects only on ischemic tissue with little or no effect noted on normal tissue. Thus, selective antagonists of the cardiac cell surface ATP-sensitive potassium channel may represent a new class of ischemia selective anti-arrhythmic medications.