Regulation of contraction and relaxation in arterial smooth muscle.
Intracellular calcium concentration ([Ca2+]i)-dependent activation of myosin light chain kinase and its phosphorylation of the 20-kd light chain of myosin is generally considered the primary mechanism responsible for regulation of contractile force in arterial smooth muscle. However, recent data suggest that the relation between [Ca2+]i and myosin light chain phosphorylation is variable and depends on the form of stimulation. The dependence of myosin phosphorylation on [Ca2+]i has been termed the "[Ca2+]i sensitivity of phosphorylation." The [Ca2+]i sensitivity of phosphorylation is "high" when relatively small increases in [Ca2+]i induce a large increase in myosin phosphorylation. Conversely, the [Ca2+]i sensitivity of phosphorylation is "low" when relatively large increases in [Ca2+]i are required to induce a small increase in myosin phosphorylation. There are two proposed mechanisms for changes in the [Ca2+]i sensitivity of phosphorylation: Ca(2+)-dependent decreases in the [Ca2+]i sensitivity of phosphorylation induced by phosphorylation of myosin light chain kinase by Ca(2+)-calmodulin protein kinase II and agonist-dependent increases in the [Ca2+]i sensitivity of phosphorylation by inhibition of a myosin light chain phosphatase. I will review the proposed mechanisms responsible for the regulation of [Ca2+]i and the [Ca2+]i sensitivity of phosphorylation in arterial smooth muscle.
Rembold
C M
CM
Department of Internal Medicine, University of Virginia School of Medicine, Charlottesville.
D000818:Animals; D001158:Arteries / Q000378:metabolism / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D006801:Humans; D009131:Muscle, Smooth, Vascular / Q000378:metabolism / Q000502:physiology*; D009218:Myosins / Q000737:chemistry / Q000378:metabolism; D009712:Nucleotides, Cyclic / Q000502:physiology; D009994:Osmolar Concentration; D010766:Phosphorylation; D014661:Vasoconstriction / Q000502:physiology*; D014664:Vasodilation / Q000502:physiology*
D009712:Nucleotides, Cyclic; D009218:Myosins; D002118:Calcium