Ca(2+)-inhibition of Ca(2+)-induced small contraction of rat uterine smooth muscle.
Ca2+ has been reported to exert an inhibitory effect on various kinds of smooth muscle. The physiological role of this inhibition is unclear. We investigated the inhibitory action of Ca2+ on the uterine smooth muscle of the rat in estrus, which shows a prominent Ca(2+)-induced inhibition. At concentrations of 0.1-30 microM Ca2+ inhibited the Ca(2+)-independent contraction of this muscle induced by oxytocin in Ca(2+)-free medium. We then investigated the inhibitory action of Ca2+ at various concentrations of Ca2+ in the bathing medium and found that Ca2+ at 1.0-10 microM also inhibited Ca(2+)-dependent contractions, which appeared phasically upon the onset of contractions. The magnitude of these phasic contractions was inversely proportional to the concentration of Ca2+ (between 1-10 microM). At 30 microM Ca2+, however, this inhibition was overcome and large pendular contractions began. Thus, the inhibition may regulate the initiation of smooth muscle contractions. The mechanism of this Ca(2+)-induced inhibition is also discussed with regard to an effect on actin.
Miyauchi
Y
Y
Department of Molecular Pharmacology, Meiji College of Pharmacy, Tokyo, Japan.
Uchida
M K
MK
D000199:Actins / Q000187:drug effects; D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002227:Carbazoles; D015638:Cytochalasin D / Q000494:pharmacology; D004347:Drug Interactions; D005260:Female; D007211:Indoles; D009130:Muscle, Smooth / Q000187:drug effects*; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors; D010121:Oxytocin / Q000502:physiology; D051381:Rats; D013449:Sulfonamides / Q000494:pharmacology; D014590:Uterine Contraction / Q000187:drug effects*; D014665:Vasodilator Agents / Q000494:pharmacology
D000199:Actins; D000470:Alkaloids; D002147:Calmodulin; D002227:Carbazoles; D007211:Indoles; D013449:Sulfonamides; D014665:Vasodilator Agents; C063769:KT 5926; D015638:Cytochalasin D; D010121:Oxytocin; C017967:W 7; D009219:Myosin-Light-Chain Kinase; D002118:Calcium