Effects of endothelium‐derived constricting factor and calcium antagonists on calcium uptake into aortic vascular smooth muscle cells

Edothelial cells in culture secrete a protein termed endothelium‐derived constricting factor (EDCF) that elicits vasoconstriction in isolated arteries. In this study, the effect of EDCF on Ca 2+ influx into cultured rat aortic smooth muscle cells and on force development in coronary arteries was evaluated and compared to that elicited by depolarization with K + . In addition, the effects of the Ca 2+ antagonists bepridil, verapamil, and nitrendipine on EDCF‐ and K + ‐induced changes in smooth muscle Ca 2+ uptake and contractile force were also quantified and compared. EDCF, but not conditioned media from control cultures of fibroblasts or pituitary cells, enhanced Ca 2+ influx into monolayer cultures of rat aortic smooth muscle cells in a time‐ and dose‐dependent manner. The time course of Ca 2+ uptake in response to EDCF was similar to that elicited by K + . EDCF also resulted in a time‐ and dose‐dependent increase in isometric force in isolated deendothelialized rings of porcine coronary artery, which was more resistant to washout than that induced by K + . The increase in both Ca 2+ influx and isometric tension induced by EDCF was abolished by heating the EDCF preparation to 80°C for 15 min. Bepridil (10 m̈M), verapamil (1 m̈M), and nitrendipine (1 m̈M) either markedly attenuated or completely blocked both EDCF‐ and K + ‐induced increases in Ca 2+ uptake and contractile force. The similarity between the effect of the Ca 2+ antagonists on K + ‐ and EDCF‐induced changes in vascular smooth muscle function suggests that a site of action of EDCF may be directed at the voltage‐sensitives Ca 2+ channel.