Endothelin and Vasoconstriction

Summary

We investigated the effect of endothelin-1 (ET) on cytosolic free Ca²⁺ concentration ( [Ca²⁺]_i) and intracellular Ca²⁺ store in vascular smooth muscle cells (VSMCs). Using quin2 microfluorometry, effects of ET on [Ca²⁺]_i were investigated in rat aortic VSMCs in primary culture. In Ca²⁺-containing solution, ET induced a rapid and sustained [Ca²⁺]_i elevation. The sustained component of [Ca²⁺]_i elevation was inhibited by diltiazem. In Ca²⁺-free solution, ET induced only a rapid and transient component of elevation, which was not inhibited by diltiazem. When the caffeine-sensitive intracellular Ca²⁺ store was depleted in Ca²⁺-free solution, ET did not increase [Ca²⁺]_i. ⁴⁵Ca²⁺ flux study showed that ET released Ca²⁺ from intracellular store in VSMCs. Front-surface fluorometry with fura-2-loaded strips of porcine coronary artery were used to simultaneously measure the effects of ET on [Ca²⁺]_i and tension development. In the Ca²⁺-containing solution, ET induced rapid and sustained increases in [Ca²⁺]_i and tension. In the Ca²⁺-free solution, ET induced rapid and transient increases in [Ca²⁺]_i and tension. Pretreatment for depletion of histamine-sensitive intracellular Ca²⁺ store did not affect ET-induced transient increases in [Ca²⁺]_i and tension in the Ca²⁺-free solution. Conversely, when the caffeine-sensitive store or both caffeine- and histamine-sensitive stores were depleted, ET induced a contraction with no change in [Ca²⁺]j. This Ca²⁺-independent contraction was markedly inhibited by H-7, a protein kinase C inhibitor. Thus, we conclude that ET-sensitive intracellular Ca²⁺ store overlaps with the caffeine-sensitive one, and that the ET-induced contraction depends on (1) Ca²⁺ release from intracellular store, (2) extracellular Ca²⁺-dependent mechanism in the sustained phase, and (3) Ca²⁺-independent mechanisms mediated by protein kinase C-related phosphorylation of contractile elements.