Ion channels and vascular tone

Ion channels in the plasma membrane of vascular muscle cells that form the walls of resistance arteries and arterioles play a central role in the regulation of vascular tone. Current evidence indicates that vascular smooth muscle cells express at least 4 different types of K+ channels, 1 to 2 types of voltage-gated Ca2+ channels, greater than or equal to 2 types of Cl- channels, store-operated Ca+ (SOC) channels, and stretch-activated cation (SAC) channels in their plasma membranes, all of which may be involved in the regulation of vascular tone. Calcium influx through voltage-gated Ca2+, SOC, and SAC channels provides a major source of activator Ca2+ used by resistance arteries and arterioles. In addition, K+ and Cl- channels and the Ca2+ channels mentioned previously all are involved in the determination of the membrane potential of these cells. Membrane potential is a key variable that not only regulates Ca+2 influx through voltage-gated Ca2+ channels, but also influences release of Ca2+ from internal stores and Ca2+- sensitivity of the contractile apparatus. By controlling Ca2+ delivery and membrane potential, ion channels are involved in all aspects of the generation and regulation of vascular tone.