Inwardly rectifying potassium channels in the regulation of vascular tone

Potassium ion (K+) channel activity is one of the major determinants of vascular muscle cell membrane potential and thus vascular tone. Four types of K+ channels are functionally important in the vasculature-Ca(2+)-activated K+ (KCa) channels, voltage-dependent K+ (Kv) channels, ATP-sensitive K+ (KATP) channels, and inwardly rectifying K+ (KIR) channels, and the latter type will be the subject of this review. Recent advances in vascular KIR channel research indicate that this channel: 1) is present in vascular muscle; 2) modulates basal arterial tone; 3) mediates powerful hyperpolarization and vasodilator responses to small but physiological increases in extracellular K+; 4) may contribute to vasodilatation in response to flow-induced shear stress; 5) may be inhibited by protein kinase C activity; 6) may be involved in vasorelaxation mediated by endothelium-derived hyperpolarizing factor; and 7) may be functionally altered in cardiovascular diseases. Vascular effects of KIR channels have so far been most extensively studied in the cerebral circulation where KIR function may be important in coupling cerebral metabolism and blood flow.