Pharmacological properties of contraction caused by sodium removal in muscle strips isolated from canine coronary artery.
Contractions produced by Na+ removal were studied in muscle strips isolated from canine coronary artery. In the presence of 20 mM K+ and 0.5 mM Ca2+, rapid contractions were observed repeatedly on complete replacement of NaCl with sucrose. This contraction in the absence of Na+ (0-Na) was not affected by phentolamine but was strongly inhibited by verapamil. Ouabain slowly potentiated the O-Na contraction and markedly reduced the inhibition due to verapamil. The O-Na contraction was dependent on external Ca2+ both with and without ouabain. Bepridil had effects very similar to those of verapamil. Amiloride and excess Mg2+ reduced the O-Na contraction and the degree of their inhibition was similar after ouabain treatment. The decrease in verapamil susceptibility could suggest that the O-Na contraction has verapamil-sensitive and -insensitive components. The former is probably due to Ca2+ influx through voltage-dependent channels and the latter to Ca2+ influx through an Na(+)-Ca2+ exchange process. Ouabain is considered to increase the contribution of Na(+)-Ca2+ exchange to the O-Na contraction. Mg2+ may inhibit both verapamil-sensitive and -insensitive pathways. Amiloride probably exerts its inhibitory effect on the contractile machinery.
Maseki
T
T
Department of Thoracic Surgery, Nagoya University, Japan.
Abe
T
T
Tomita
T
T
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001158:Arteries; D015764:Bepridil / Q000494:pharmacology; D003331:Coronary Vessels / Q000187:drug effects*; D004285:Dogs; D005260:Female; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology; D010646:Phentolamine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology*; D014700:Verapamil / Q000037:antagonists & inhibitors / Q000494:pharmacology
D010042:Ouabain; D015764:Bepridil; D000584:Amiloride; D012964:Sodium; D014700:Verapamil; D011188:Potassium; D010646:Phentolamine