Abstract
In order to investigate the effects of Ca 2+, Ba 2+ and Sr 2+ on vascular endothelial nitric oxide (NO) production, contractile and relaxant responses of porcine depolarized coronary arteries to these divalent cations were compared. In the presence of diltiazem, Ba 2+ induced NO-dependent relaxation, Sr 2+ did slightly and Ca 2+ did not; however all three cations increased cGMP levels in endothelium-intact arteries to similar extents. In the absence of diltiazem, these cations evoked contractions: the EC 50 of Ca 2+ for endothelium-denuded arteries was lower than those of Ba 2+ and Sr 2+. The IC 50 of diltiazem for arteries precontracted with Ca 2+ was higher than for arteries precontracted with Ba 2+ and Sr 2+. These results suggest that Ba 2+ and Sr 2+, as well as Ca 2+, activate coronary arterial NO production, and also that the different responses of coronary arteries to these divalent cations can be explained, in part, by the different sensitivities of the smooth muscle to these cations and by the different potencies of diltiazem to inhibit the contractions the cations induced.
Published Version
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