Properties of smooth muscle hyperpolarization and relaxation to K+ in the rat isolated mesenteric artery.
Smooth muscle membrane potential and tension in rat isolated small mesenteric arteries (inner diameter 100-200 microm) were measured simultaneously to investigate whether the intensity of smooth muscle stimulation and the endothelium influence responses to exogenous K+. Variable smooth muscle depolarization and contraction were stimulated by titration with 0.1-10 microM phenylephrine. Raising external K+ to 10.8 mM evoked correlated, sustained hyperpolarization and relaxation, both of which were inhibited as the smooth muscle depolarized and contracted to around -38 mV and 10 mN, respectively. At these higher levels of stimulation, raising the K+ concentration to 13.8 mM still hyperpolarized and relaxed the smooth muscle. Relaxation to endothelium-derived hyperpolarizing factor, released by ACh, was not altered by the level of stimulation. In endothelium-denuded arteries, the concentration-relaxation curve to K+ was shifted to the right but was not depressed. In denuded arteries, relaxation to K+ was unaffected by the extent of prior stimulation and was blocked with 0.1 mM ouabain but not with 30 microM Ba2+. The ability of K+ to stimulate simultaneous hyperpolarization and relaxation in the mesenteric artery is consistent with a role as an endothelium-derived hyperpolarizing factor activating inwardly rectifying K+ channels on the endothelium and Na+-K+-ATPase on the smooth muscle cells.
Dora
K A
KA
Department of Pharmacy and Pharmacology, University of Bath, Bath BA2 7AY, United Kingdom.
Garland
C J
CJ
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D001685:Biological Factors / Q000378:metabolism / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D017538:Mesenteric Artery, Superior / Q000187:drug effects / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism* / Q000494:pharmacology; D051381:Rats; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D001685:Biological Factors; D004791:Enzyme Inhibitors; D014662:Vasoconstrictor Agents; C067410:endothelium-dependent hyperpolarization factor; D010656:Phenylephrine; D001464:Barium; D010042:Ouabain; D000109:Acetylcholine; D011188:Potassium; D019331:NG-Nitroarginine Methyl Ester