Role of smooth muscle cells on endothelial cell cytosolic free calcium in porcine coronary arteries

We tested the hypothesis that the cytosolic free calcium concentration in e ndothelial cells is under the influence of the smooth muscle cells in the c oronary circulation. In the left descending branch of porcine coronary arte ries, cytosolic free calcium concentration ([Ca2+](i)) was estimated by det ermining the fluorescence ratio of two calcium probes, fluo 4 and fura red, in smooth muscle and endothelial cells using confocal microscopy. Acetylch oline and potassium, which act directly on smooth muscle cells to increase [Ca2+](i), were found to indirectly elevate [Ca2+](i) in endothelial cells; in primary cultures of endothelial cells, neither stimulus affected [Ca2+] (i), yet substance P increased the fluorescence ratio twofold. In response to acetylcholine and potassium, isometric tension developed by arterial str ips with intact endothelium. was attenuated by up to 22% (P < 0.05) compare d with strips without endothelium. These findings suggest that stimuli that increase smooth muscle [Ca2+](i) can indirectly influence endothelial cell function in porcine coronary arteries. Such a pathway for negative feedbac k can moderate vasoconstriction and diminish the potential for vasospasm in the coronary circulation.