A selective inhibitor of cAMP-specific phosphodiesterase, Ro 20–1724, has no effect on the quantal release of acetylcholine from the mouse phrenic nerve

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Abstract
The indirect twitch response of the mouse isolated phrenic nerve-diaphragm preparation, partially paralysed by tubocurarine, was restored only by about 10% by Ro 20–1724 at 2 to 280 μM. The solvent vehicle, dimethylsulphoxide, also showed the same effect to a similar extent. Intracellular recordings with glass microelectrodes revealed that Ro 20–1724 (40 μM) affected neither the resting membrane potential, the amplitude and frequency of miniature endplate potentials nor the amplitude of nerve-impulse evoked endplate potentials recorded in curarized preparations. The result indicates that Ro 20–1724 at a concentration four times the IC50 of phosphodiesterase inhibition has no effect on the quantal release of acetylcholine from a mammalian motor nerve and suggests that cAMP has no modulatory effect on the transmitter release.