Endothelial Cell-Derived Vasoconstrictors

Abstract

Intercellular signaling between the endothelial cell (EC) and vascular smooth muscle (VSM) is an important determinant of vasomotor tone. We evaluated mechanisms of action of EC-derived constrictors on VSM using conditioned medium from bovine aortic ECs in culture (EC-CM) or endothelin-1 (ET-1), and isolated coronary arteries or cultured VSM cells. EC-CM enhanced Ca2+ uptake into monolayers of rat aortic VSM and elicited sustained contractions in isolated coronary vessels in a time- and dose-dependent manner. The enhanced Ca2+ uptake and contractions were markedly attenuated by the Ca2+ channel antagonists bepridil, verapamil, and nitrendipine. EC-CM and ET-1 resulted in VSM membrane depolarization and increased excitability to electrical stimulation that was blocked by verapamil. ET-1 and EC-CM induced a dose-dependent increase in steady-state [Ca2+]i in Fura-2-loaded rat VSM cells. Most VSM responded with a rapid and transient increase in [Ca2+]i while others lacked only the transient phase. The elevated poststimulus [Ca2+]i level appeared to precede the influx of extracellular Ca2+ and contraction. EC-CM and ET-1 also resulted in time- and concentration-dependent increases in inositol monophosphate (IP) formation in rat aorta that paralleled the development of isometric force. We propose a biphasic mechanism in which the stable constrictors present in EC-CM elicit a rapid, phospholipase C-mediated mobilization of intracellular Ca2+ accompanied by or coupled to a sustained influx of extracellular Ca2+ through voltage-dependent channels.