Endothelium-dependent relaxation and hyperpolarization of canine coronary artery smooth muscles in relation to the electrogenic Na-K pump.
1 In the smooth muscle cells of canine coronary artery, acetylcholine (ACh) produced a transient, endothelium-dependent hyperpolarization of the membrane. A similar hyperpolarization was also elicited by exposure to Krebs solution after incubation of the artery in K-free solution for 30 min. 2 A hyperpolarization of reproducible amplitude was generated when ACh was applied at intervals greater than 30 min. Repetitive application of ACh at 15 min intervals caused a successive reduction in the amplitude of hyperpolarization. 3 The reduction in the amplitude of relaxation during five successive applications of ACh at 15 min intervals was less than 10% of the first relaxation. 4 The ACh-induced hyperpolarization was blocked by atropine but not by ouabain, whereas the K-free induced hyperpolarization was blocked by ouabain. In low Na (Li-substituted) solution, ACh still induced a hyperpolarization but the K-free induced hyperpolarization was absent. 5 In coronary artery precontracted by high-K solution, ACh produced an endothelium-dependent relaxation, without membrane hyperpolarization. The associated relaxation was resistant to ouabain but sensitive to atropine. 6 It is concluded that in the canine coronary artery, the electrogenic Na-K pump does not contribute to the endothelium-dependent hyperpolarization or relaxation. The results are consistent with the release of two different inhibitory factors from the vascular endothelium.
Chen
G
G
Department of Pharmacology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Hashitani
H
H
Suzuki
H
H
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D003331:Coronary Vessels / Q000502:physiology; D004285:Dogs; D004730:Endothelium, Vascular / Q000502:physiology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D066298:In Vitro Techniques; D008094:Lithium / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D010042:Ouabain; D008094:Lithium; D012964:Sodium; D000109:Acetylcholine; D011188:Potassium