Effects of ouabain on muscle tension and intracellular Ca2+ level in guinea-pig aorta.
The effects of ouabain on muscle tension and the intracellular Ca2+ level ([Ca2+]i) were examined in guinea-pig aorta loaded with fura-2. Ouabain caused a gradual and sustained increase in both [Ca2+]i and muscle tension. There was a positive correlation between these two parameters. In Ca(2+)-free solution, ouabain did not affect either [Ca2+]i or muscle tension, suggesting that the ouabain-induced increase in [Ca2+]i was not due to Ca2+ release from storage sites. The ouabain-induced increase in [Ca2+]i and muscle tension was inhibited by Ni2+, which inhibits the Na+/Ca2+ exchanger, but not by verapamil. Furthermore, anionic and cationic amphiphiles were used as modulators of the Na+/Ca2+ exchanger. Sodium dodecyl sulfate accelerated the responses to ouabain, whereas dodecyltrimethylammonium bromide inhibited them. These results suggest that in the guinea-pig aorta, ouabain induces contraction by increasing the Ca2+ influx through the Na+/Ca2+ exchanger on the plasma membrane, but not through verapamil-sensitive Ca2+ channels.
Iwamoto
T
T
Department of Pharmacology, Kanebo Ltd., Osaka, Japan.
Harada
K
K
Nakajima
F
F
Sukamoto
T
T
D000818:Animals; D001011:Aorta / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004558:Electric Stimulation; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D009532:Nickel / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger; D014700:Verapamil / Q000494:pharmacology
D002352:Carrier Proteins; D000644:Quaternary Ammonium Compounds; D019831:Sodium-Calcium Exchanger; D012967:Sodium Dodecyl Sulfate; D010042:Ouabain; C022838:nickel chloride; D009532:Nickel; D014700:Verapamil; C022806:dodecyltrimethylammonium; D002118:Calcium