Vascular smooth muscle

Vascular smooth muscle consists of contractile cells in blood-vessel walls that change vessel diameter. Its contraction and relaxation help regulate blood flow and blood pressure.

Calcium-induced calcium release: A process in which calcium entering a cell triggers further calcium release from intracellular stores. Calcium signals raise cytosolic calcium and initiate contraction in vascular smooth muscle.
Smooth muscle: A type of involuntary, nonstriated muscle found in the walls of hollow organs and vessels. Vascular smooth muscle is the smooth-muscle tissue specialized for blood vessels.
Vasoconstriction: Narrowing of a blood vessel caused by contraction of its muscular wall. Vascular smooth-muscle contraction directly produces vasoconstriction.
Endothelium: The thin layer of cells lining blood vessels and other body cavities. Endothelial signals, including nitric oxide and endothelin, regulate adjacent smooth muscle.
Myosin light-chain kinase: An enzyme that phosphorylates myosin light chains, enabling smooth-muscle myosin to interact with actin. It converts calcium-calmodulin signals into the phosphorylation that starts contraction.
Actin: A protein that forms filaments used in cell structure and muscle contraction. Actin filaments interact with myosin to generate force in vascular smooth-muscle cells.
Vasodilation: Widening of a blood vessel caused by relaxation of its muscular wall. Relaxation of vascular smooth muscle allows vessels to dilate.
Pericyte: A contractile cell associated with capillaries and small venules that helps support and regulate microvessels. Pericytes occupy smaller-vessel niches and are distinct from the smooth-muscle layer of larger vessels.
Rho-associated protein kinase: A kinase that regulates cell functions, including smooth-muscle contraction, by phosphorylating target proteins. It increases contractile force by inhibiting myosin light-chain phosphatase.
Myosin: A family of motor proteins that use ATP to move along actin filaments. Smooth-muscle myosin generates the force that narrows or widens vessels.

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