Endothelin Dissociates Muscle Tension from Cytosolic Ca²⁺ in Vascular Smooth Muscle of Rat Carotid Artery

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Endothelin induced rapid increase followed by a decrease in cytosolic Ca²⁺ ([Ca²⁺]i) and a slow increase in muscle tension in the vascular smooth muscle strip of rat carotid artery. Thus, the endothelin-induced contraction was smaller, and it, became gradually greater than high K-induced contraction at a given [Ca²⁺], i. In Ca²⁺-free solution, endothelin induced a transient increase in [Ca²⁺]i and a sustained contraction. These results suggest that endothelin-induced contraption is due to the increase in [Ca²⁺]i, the time-dependent change in Ca²⁺-sensitivity of contractile elements, and the mechanism which is independent of the increment in [Ca²⁺]i.