Possible mechanisms of stimulatory action of papaverine on calcium-uptake by rat uterine microsomal fraction.

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Abstract
Effects of papaverine [a non-specific smooth muscle relaxant] and cAMP on Ca-uptake by the microsomal fraction from rat uterus were studied. Papaverine (3 .times. 10-5 M) potentiated Ca-uptake by the microsomal fraction in the presence of potassium oxalate. cAMP and MIX (3-isobutyl-1-methylxanthine; 1 mM), a potent phosphodiesterase inhibitor, did not influence Ca-uptake by the microsomal fraction in the presence of potassium oxalate. CAMP in concentrations of 10-8-10-4 M did not influence Ca-uptake by the microsomal fraction in the presence of potassium oxalate. In the absence of potassium oxalate, papaverine and aspaminol (1,1-diphenyl-3-piperidinobutanol hydrochloride), a nonspecific smooth muscle relaxant, inhibited Ca-uptake by the microsomal fraction and cAMP had no influence on this uptake. Papaverine potentiated Ca-uptake by membranes such as sarcoplasmic reticulum, in the presence of potassium oxalate and inhibited Ca-uptake by the plasma membrane-derived vesicles in the absence of potassium oxalate. Smooth muscle relaxation by papaverine is related to a cAMP-independent mechanism and to a mechanism mediated by cAMP.

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