TEA inhibits ACh-induced EDRF release: endothelial Ca(2+)-dependent K+ channels contribute to vascular tone.
The effects of K(+)-channel blockers on the acetylcholine (ACh)-induced relaxation of vascular smooth muscle, intracellular free Ca2+ concentration ([Ca2+]i) elevation, and ACh-evoked outward K+ current of endothelial cells of rabbit aorta were studied using bioassay, spectrofluorimetry, and patch-clamp techniques, respectively. In bioassay experiments, ACh caused relaxation of endothelium-denuded aortic rings in a concentration-dependent manner when perfused through an endothelium-intact donor segment of aorta but not when perfused directly onto the recipient aortic ring. ACh-induced relaxation was inhibited by perfusion of tetraethylammonium ions (TEA; 5 mM) through the donor but not by perfusion directly onto the recipient segment. Glibenclamide had no effect on ACh-induced relaxation of the bioassay ring in either situation. ACh increased [Ca2+]i at the endothelial surface of aortic strips but not at the adventitial surface. TEA inhibited ACh-induced [Ca2+]i elevation, whereas glibenclamide had no effect. In patch-clamp experiments with freshly isolated endothelial cells, ACh evoked a biphasic outward current which was completely abolished by TEA (3 mM). It is concluded that Ca(2+)-dependent K+ channels are important for increasing [Ca2+]i during agonist stimulation and consequently for the synthesis/release of endothelium-derived relaxing factors (EDRFs). Furthermore, endothelial ATP-sensitive K+ channels do not contribute to ACh-induced relaxation or evoke an increase in endothelial [Ca2+]i of rabbit thoracic aorta.
Demirel
E
E
Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, Florida 33101.
Rusko
J
J
Laskey
R E
RE
Adams
D J
DJ
van Breemen
C
C
D000109:Acetylcholine / Q000494:pharmacology*; D000818:Animals; D001011:Aorta / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D001681:Biological Assay; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D005260:Female; D007425:Intracellular Membranes / Q000378:metabolism; D008297:Male; D009569:Nitric Oxide / Q000037:antagonists & inhibitors*; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000502:physiology*; D011817:Rabbits; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology*; D014664:Vasodilation / Q000187:drug effects; D014666:Vasomotor System / Q000502:physiology*
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D013757:Tetraethylammonium Compounds; D009569:Nitric Oxide; D019789:Tetraethylammonium; D000109:Acetylcholine; D002118:Calcium