POTASSIUM CHANNELS IN VASCULAR SMOOTH-MUSCLE

1. Regulation of smooth muscle membrane potential through changes in K + channel activity and subsequent alterations in the activity of volta ge-dependent calcium channels is a major mechanism of vasodilation and vasoconstriction, both in normal and pathophysiological conditions. T he contribution of a given K+ channel type to this mechanism of vascul ar regulation depends on the vascular bed and species examined. 2. Mul tiple K+ channels are present in most vascular smooth muscle cells and these different K+ channels play unique roles in regulating vascular tone. Voltage-dependent K+ (K-v) channels are activated by depolarizat ion, may contribute to steady state resting membrane potential and are inhibited by certain vasoconstrictors. Calcium-activated K+ (K-Ca) ch annels oppose the depolarization associated with intrinsic vascular to ne and are activated by some endogenous vasodilators. Small-conductanc e, apamin-sensitive K-Ca channels may be activated by endothelium-deri ved hyperpolarizing factor. ATP-sensitive K+ (K-ATP) channels are acti vated by pharmacological and endogenous vasodilators. Inward rectifier K+ (K-ir) channels are activated by slight changes in extracellular K + and may contribute to resting membrane potential. 3. Membrane potent ial and diameter are determined, in part, by the integrated activity o f several K+ channels, which are regulated by multiple dilator and con strictor signals in vascular smooth muscle.