Hyperpolarization and increased free calcium in acetylcholine-stimulated endothelial cells

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Abstract
In freshly harvested aortic endothelial cells from rabbits, some cellular events associated with stimulation by acetylcholine (ACh) were analyzed. ACh (3 .mu.M) induced a transient hyperpolarization of 8.3 .+-. 2.5 mV, which peaked within 3-5 s and subsequently declined with a similar time course. Hyperpolarization was caused by a transient Ca2+-dependent outward current (IoACh), which was mainly carried by K+. ACh (3 and 10 .mu.M) also evoked transient dose-dependent increases in the intracellular free Ca2+ concentration (Cai2+). Pretreatment with atropine (1 and 3 .mu.M) abolished both responses to ACh, the increase in Cai2+ as well as the transient outward current. It is concluded that IoACh and the rise in Cai2+ are two manifestations of muscarinic receptor stimulation. The rise in Cai2+ might be the primary event, leading to secondary membrane hyperpolarization.