ATP-dependent potassium channels of muscle cells: their properties, regulation, and possible functions

ATP-dependent potassium channels are present at high density in the membranes of heart, skeletal, and smooth muscle and have a low Popen at physiological [ATP]i. The unitary conductance is 15-20 pS at physiological [K+]o, and the channels are highly selective for K+. Certain sulfonylureas are specific blockers, and some K channel openers may also act through these channels. KATP channels are probably regulated through the binding of ATP, which may in turn be regulated through changes in the ADP/ATP ratio or in pHi. There is some evidence for control through G-proteins. The channels have complex kinetics, with multiple open and close states. The main effect of ATP is to increase occupancy of long-lived close states. The channels may have a role in the control of excitability and probably act as a route for K+ loss from muscle during activity. In arterial smooth muscle they may act as targets for vasodilators.