ACh-induced calcium transients in primary cultures of rabbit aortic endothelial cells

Acetylcholine (ACh) causes vascular smooth muscle relaxation by releasing endothelium-derived relaxing factor (EDRF) from endothelial cells (EC). Although a pivotal role for cytosolic free Ca2+ ([Ca2+]i) has been implicated in the generation and/or release of EDRF by various agonists, there is no conclusive evidence showing that ACh increases [Ca2+]i in EC. In the present study, using the Ca2+-sensitive fluorescent indicator fura-2, we show for the first time that ACh (10(-5) M) increases [Ca2+]i six- to sevenfold above prestimulus levels in primary cultures of rabbit aortic EC (RbAEC). ACh effects are dose dependent [effective concentration producing 50% of the maximum response (EC50) approximately 9 X 10(-7) M] and are blocked by atropine, a selective muscarinic receptor antagonist. The [Ca2+]i increase is due both to the mobilization of intracellular Ca2+ and to the influx of extracellular Ca2+. A 5-min incubation of RbAEC with 4 beta-phorbol 12-myristate 13-acetate (10(-7) M) inhibits ACh-induced [Ca2+]i transients, suggesting that the signaling pathway involved in ACh receptor signal transduction may be modulated via protein kinase C. These cultured EC provide a unique in vitro model system for studying mechanisms involved in ACh-induced EDRF release.