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Abstract The effects of papaverine, isoprenaline and N6,2′-O-dibutyryl 3′,5′-cyclic adenosine monophosphate (DiBu.C-AMP) on calcium movements in the taenia from the guinea-pig caecum have been investigated and compared with the effects of phenylephrine. Papaverine and DiBu.C-AMP antagonized the contraction of KCl-depolarized muscle induced by CaCl2 and increased 45Ca-efflux from the taenia. Papaverine also significantly depressed 45Ca-uptake by this preparation. These findings suggest that papaverine impairs the availability of calcium to the contractile system and that there may be a correlation between relaxation and increase of 45Ca-efflux. The action of DiBu.C-AMP resembles that of papaverine but its potency is less.
Tomiyama et al. (1973) studied this question.