title: Role of calcium in endothelium-dependent relaxation of arterial smooth muscle.
abstract: Endothelium-dependent relaxation was studied in rings of rabbit thoracic aorta. Relaxation responses were induced with methacholine, the calcium ionophore A23187 and maitotoxin before and after removal of Ca++ from the external medium; in the presence of calcium-channel entry blockers (verapamil and nifedipine); or with trifluoperazine. Deletion of Ca++ greatly impaired responses to all 3 agonists while trifluoperazine only blocked cholinergic-induced relaxation. The calcium-channel blockers had effects that were concentration- and time-dependent, but their action included blockade of A23187. Cytosolic-free Ca++ concentrations were measured in cultured endothelial cells after incubation of the cells with 10 microM Fura-2/AM or 50 microM Quin 2/AM. Bradykinin (1 X 10(-10) to 1 X 10(-7) M) and melittin (0.5 to 5 micrograms/ml) caused dose-dependent increases in intracellular Ca++ with maximal responses at 3 X 10(-8) M and 3 micrograms/ml, respectively. Both agents were able to induce an increase in cytosolic-free Ca++ in the presence of EGTA (1.5 X 10(-3) M) or verapamil (1 X 10(-5) M). The plateau phase of the Ca++ transient appeared to be modified slightly by verapamil, while the peak responses and plateau were attenuated by '0' Ca++/EGTA. To assess a function of the endothelium, production of endothelium-derived relaxing factor (EDRF) was studied in cells grown on microcarrier beads superfused in a column, and the column effluent was bioassayed on aortic rings.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001158:Arteries / Q000502:physiology*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000502:physiology*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002417:Cattle; D004727:Endothelium / Q000502:physiology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects; D008297:Male; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D009569:Nitric Oxide; D011817:Rabbits; D014665:Vasodilator Agents / Q000378:metabolism
chemical_list: D002147:Calmodulin; D007473:Ion Channels; D008688:Methacholine Compounds; D014665:Vasodilator Agents; D016210:Methacholine Chloride; D009569:Nitric Oxide; D000001:Calcimycin; D002118:Calcium