This study examined the inhibitory effects of papaverine on twitches directly elicited by electrical stimulation of the mouse diaphragm. Papaverine (3–100 µM) inhibited twitches in a dose-dependent manner. Papaverine increased the cyclic adenosine monophosphate (cAMP) but not cyclic guanosine monophosphate (cGMP) content. IBMX, Db-cAMP and 8-br-cGMP did not affect twitches, whereas verapamil and NaCN inhibited twitches. Increases in extracellular Ca²⁺ removed the twitch inhibition caused by verapamil but not that caused by papaverine. Papaverine (30 and 100 µM) and NaCN (1 mM) decreased creatine phosphate and ATP contents. These results suggest that the relaxing effects of papaverine on mouse diaphragm are mainly due to inhibition of aerobic energy metabolism.

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