Ca2+ localization and sensitivity in vascular smooth muscle.
An increase in cytosolic Ca2+ level ([Ca2+]i) is a prerequisite for smooth muscle contraction. Simultaneous measurements of [Ca2+]i and muscle tension give direct information on the Ca2+ regulation of smooth muscle. The photoprotein aequorin and the fluorescent Ca2+ indicator fura-2 are widely used for this purpose. Although there are some inconsistencies between the results obtained with these two indicators, comparison between [Ca2+]i and muscle tension in vascular smooth muscle indicates that stimulation of alpha-adrenoceptors increases, whereas stimulation of beta-adrenoceptors decreases, both the Ca2+ sensitivity of contractile elements and [Ca2+]i. Thus, as Hideaki Karaki explains, contractility of vascular smooth muscle may be regulated not only by [Ca2+]i but also by the Ca2+ sensitivity of the contractile elements.
Karaki
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D000818:Animals; D002118:Calcium / Q000032:analysis / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000502:physiology*
D002118:Calcium