Inhibitory Actions of Endothelial Products on Mechanical and Calcium Responses in Aortic Smooth Muscle Cells.

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Abstract
The effects of endothelial products on intracellular calcium ion concentrations ([Ca2+]i) were investigated in the guinea-pig aorta. The perfusate of bradykinin-stimulated cultured endothelial cells relaxed aortic rings by approximately 70%; it was reduced to approximately 50% by nitroarginine, to approximately 30% in high-K solution and remained unaltered by indomethacin. The perfusate elevated the cyclic GMP content in the muscle, which was inhibited by nitroarginine. In cultured, aortic muscle cells, bradykinin elevated [Ca2+]i with an initial transient and following sustained phase; the former was absent after treatment with cyclopiazonic acid while the latter was abolished in [Ca2+]o-free medium. The perfusate lowered aortic [Ca2+]i, and this action was weakened by nitroarginine and diminished in high-K solution. Therefore, the perfusate reduced aortic [Ca2+]i with and without an increase in cyclic GMP production. These actions were sensitive to nitroarginine and high-K, respectively, suggesting that the perfusate contained at least two relaxants, EDRF and EDHF, with both lowering [Ca2+]i in aortic muscle mainly by inhibiting Ca2+ influx.

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