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 - Ca2+ activated K+ (K-Ca) channels, voltage-dependent K+ (K-V) channels, ATP-sensitive K+ (K-ATP) channels, and inwardly rectifying K+ (K-IR) channels, and the latter type will be the subject of this review. Recent advances in vascular K-IR 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 K-IR channels have so far been most extensively studied in the cerebral circulation where K-IR function may be important in coupling cerebral metabolism and blood flow.