NONSPECIFIC RELAXATION OF INTESTINAL SMOOTH MUSCLE INDUCED BY ANTISPASMODICS AND MOVEMENT OF CALCIUM IONS

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Abstract
The effects of benactyzine and papaverine on Ca-uptake by a microsomal fraction obtained from rabbit taenia coli and Ca-contraction of a KCl-depolarized smooth muscle, and influence of external Ca2+ on inhibitory actions of the drugs on the smooth muscle contraction induced by histamine were studied. Potentiation of Ca-uptake by papaverine in the concentration of 3 .times. 10-5 M may be due to the increase of cyclic[c]AMP as the result of the inhibition of cyclic AMP phosphodiesterase. Papaverine in the concentration of 10-4 M did not potentiate Ca-uptake, notwithstanding that the concentration of papaverine used was higher. The noncompetitive antihistaminergic activity of papaverine was significantly decreased by increase in the external Ca-concentration. This effect of external Ca2+ was clearly demonstrated in the experiments with benactyzine which had little inhibitory action on phosphodiesterase activity. In intestinal smooth muscle, papaverine may have inhibitory actions on Ca-uptake by microsomal fraction in addition to the stimulatory action which seems to be mediated through cAMP. Relaxing action of papaverine in the intestinal smooth muscle may be due to both actions, thus decreasing the supply of Ca2+ to the contractile elements.