CPA induces a sustained increase in [Ca2+]i of endothelial cells in situ and relaxes porcine coronary artery.

Using fura 2 fluorometry, we investigated the effect of cyclopiazonic acid (CPA), an inhibitor of Ca2+ pump adenosinetriphosphatase of the endoplasmic reticulum, on cystosolic Ca2+ concentration ([Ca2+]i) and tension in porcine aortic valvular endothelial cells and coronary arterial strips with endothelium. In normal physiological salt solution, CPA induced a sustained increase in [Ca2+]i in the valvular strips, whereas in Ca(2+)-free physiological salt solution, CPA elicited a transient elevation of [Ca2+]i. CPA(30 microM) relaxed coronary strips with endothelium precontracted by 100 nM U-46619; this relaxation was partially inhibited by N omega-nitro-L-arginine (100 microM). These results indicate that the CPA-induced increase in [Ca2+]i depends on the Ca2+ release and the Ca2+ influx in the endothelial cells in situ and that the CPA-induced endothelium-dependent decreases in [Ca2+]i and tension in the smooth muscle are due to the combined effect of N omega-nitro-L-arginine-sensitive and -resistant factors.