A dual effect of acetylcholine on gastropod smooth muscle preparations.

At the neuromuscular junction of certain molluscan smooth muscles acetylcholine (ACh) is thought to be released by motoneuron activity eli­ citing muscle contraction 1. The discovery, however, that isolated gastropod smooth muscle preparations are not very sensitive to exogenously applied ACh2> 3 and that constant maximum contraction amplitudes were only obtained after 4 or 5 succes­ sive administrations of ACh (Fig. 1 a) should not be ignored. In this connection it is important to remember that the action of ACh may be artifactual in the sense that the initial purely excitatory effect S Q 10631 5 x l O '5