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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.

Type

Journal article

Journal

Am J Physiol Heart Circ Physiol

Publication Date

06/2001

Volume

280

Pages

H2424 - H2429

Keywords

Acetylcholine, Animals, Barium, Biological Factors, Dose-Response Relationship, Drug, Enzyme Inhibitors, In Vitro Techniques, Male, Membrane Potentials, Mesenteric Artery, Superior, Muscle, Smooth, Vascular, NG-Nitroarginine Methyl Ester, Ouabain, Phenylephrine, Potassium, Rats, Vasoconstrictor Agents