POTASSIUM CHANNELS IN VASCULAR SMOOTH MUSCLE

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Abstract
SUMMARY: 1. Regulation of smooth muscle membrane potential through changes in K+ channel activity and subsequent alterations in the activity of voltage‐dependent calcium channels is a major mechanism of vasodilation and vasoconstriction, both in normal and pathophysiological conditions. The contribution of a given K+ channel type to this mechanism of vascular regulation depends on the vascular bed and species examined.2. Multiple 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+ (Kv) channels are activated by depolarization, may contribute to steady state resting membrane potential and are inhibited by certain vasoconstrictors. Calcium‐activated K+ (KCa) channels oppose the depolarization associated with intrinsic vascular tone and are activated by some endogenous vasodilators. Small‐conductance, apamin‐sensitive KCa channels may be activated by endothelium‐derived hyperpolarizing factor. ATP‐sensitive K+ (KATP) channels are activated by pharmacological and endogenous vasodilators. Inward rectifier K+ (Kir) channels are activated by slight changes in extracellular K+ and may contribute to resting membrane potential.3. Membrane potential and diameter are determined, in part, by the integrated activity of several K+ channels, which are regulated by multiple dilator and constrictor signals in vascular smooth muscle.