The effects of Ca2+ antagonists on Ca2+ accumulation by subcellular fractions of rat myometrium.
Several agents which antagonize or interact with Ca2+ in the excitation-contraction coupling of smooth muscle have been tested for their effects on Ca2+ accumulation by subcellular fractions of the rat uterus. Na+, but not K+, reduced the amount of Ca2+ that could be accumulated by the plasma membrane fraction (PM) and the endoplasmic reticular fraction (ER). Sr2+ considerably reduced Ca2+ accumulation by PM, ER, and the mitochondrial fraction; Ba2+ had a similar effect but was not as potent as Sr2+. La3+ at concentrations up to 10 mM was unable to block Ca2+ accumulation by PM and ER completely. The pharmacological agents D600, verapamil, and chlorpromazine all inhibited Ca+ accumulation at dose levels much higher than those required to inhibit contractility, and were ineffective at lower doses. The action of Ca2+ antagonists is seen to be complex, involving interactions at different sites and on different processes. For a fuller understanding of their mechanisms of action further studies upon passive binding and on the release of Ca2+ from subcellular sites are required.
D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002413:Cations, Divalent / Q000494:pharmacology; D002746:Chlorpromazine / Q000494:pharmacology; D005260:Female; D005711:Gallopamil / Q000494:pharmacology; D007811:Lanthanum / Q000494:pharmacology; D009215:Myometrium / Q000378:metabolism* / Q000648:ultrastructure; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000494:pharmacology; D013347:Subcellular Fractions / Q000378:metabolism; D014599:Uterus / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology
D002413:Cations, Divalent; D005711:Gallopamil; D007811:Lanthanum; D012964:Sodium; D014700:Verapamil; D011188:Potassium; D002118:Calcium; D002746:Chlorpromazine