Regulation of cytoplasmic Ca2+ in vascular smooth muscle

The vascular smooth muscle of conduit arteries can be excited by either depolarization or agonists. The former stimulus opens potential sensitive Ca2+ channels in the plasmalemma and releases bound Ca2+ from its outer surface. Ne interacts with alpha-receptors to open receptor operated Ca2+ channels which are distinct from the PSCs and also liberates surface bound Ca2+. In addition, it releases "trigger" Ca2+ from the inner plasmalemmal surface which in turn induces Ca2+ release from the sarcoplasmic reticulum. The elevated cytoplasmic free Ca2+ then combines with calmodulin to stimulate myosin light-chain kinase.