Roles of calcium and the endothelium in the relaxations produced by 5'-N-ethylcarboxamidoadenosine (NECA)

The aim of the present investigation was to evaluate the endothelium dependency in the relaxations by the adenosine analog, 5'-N-ethylcarboxamidoadenosine (NECA), and the requirement for extracellular calcium in endothelium-dependent and independent relaxations. In prostaglandin F2 alpha (PGF2 alpha)-contracted bovine coronary arteries with intact endothelium, bradykinin produced relaxations in calcium medium but not in calcium-free medium. Removal of the endothelium abolished the relaxing response to bradykinin. In calcium medium, NECA produced similar relaxations in coronary arteries with intact and mechanically disrupted endothelium. The relaxation-response curves for NECA were shifted to the right in parallel in calcium free medium. Sodium nitroprusside produced concentration-dependent relaxations which were endothelium-independent. Removal of calcium from the bathing medium caused partial but significant attenuation of these relaxations. The results indicated that in bovine coronary artery, relaxations induced by NECA were endothelium-independent. Also bradykinin-induced relaxations are totally dependent on calcium whereas the endothelium-independent relaxing agents such as NECA and sodium nitroprusside require calcium only partially for their relaxations.