Effects of nonspecific smooth muscle relaxants on calcium-uptake by microsomal fraction and their inhibitory action in rabbit taenia coli.

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Abstract
Effects of nonspecific smooth muscle relaxants, papaverine and Aspaminol (1,1-diphenyl-3-piperidinobutanol hydrochloride), on Ca uptake by a microsomal fraction and mechanical activity in the rabbit tenia coli were studied. Papaverine, which inhibits cyclic[c]AMP phosphodiesterase, increased Ca uptake by the microsomal fraction in a concentration of 10-5 M but not in a concentration of 10-4 M. Potentiation of Ca uptake by papaverine is probably due to the increase of cAMP due to the inhibition of phosphodiesterase. Aspaminol, which has little inhibitory action on phosphodiesterase activity, inhibited Ca uptake by the microsomal fraction. This inhibition by Aspaminol was abolished by the increase of Ca concentration in the reaction medium. Non-competitive antihistaminic activity of Aspaminol was considerably reduced by an increase of the external Ca concentration, while an increase of the external Ca concentration slightly decreased the antihistaminic activity of papaverine. Contraction of KCl-depolarized tenia coli induced by CaCl2 was inhibited competitively by Aspaminol and noncompetitively by papaverine. Aspaminol competes with Ca ions at a surface site of the muscle membrane concerned with the Ca uptake process, thus decreasing the supply of Ca ions to the contractile elements, and papaverine may have inhibitory actions on Ca uptake by the microsomal fraction in addition to a stimulatory action which seems to be mediated through cAMP. These actions on Ca uptake may induce smooth muscle relaxation.