Effects of 5-hydroxytryptamine, dopamine, and acetylcholine on accumulation of cyclic AMP and cyclic GMP in the anterior byssus retractor muscle ofMytilus edulis L. (Mollusca)

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Abstract
We investigated in vitro accumulation of adenosine 3′,5′-monophosphate (induced by 5-hydroxytryptamine and dopamine) and of guanosine 3′,5′-monophosphate (induced by acetylcholine) in the anterior byssus retractor muscle ofMytilus. The response to 5-hydroxytryptamine exceeded that induced by equimolar concentrations of dopamine. 1-methyl lysergic acid, a 5-hydroxytryptamine-blocking agent, diminished the 5-hydroxytryptamine-induced increase of cyclic AMP level. This parallels the effect of this amine on the contracted muscle. Acetylcholine, which causes a tonic contraction of the muscle, increased intracellular levels of cyclic GMP in a dose-dependent (max. 45-fold at 10−4 M ACh) manner. The time course of the rise in cyclic GMP level was rapid and transient (peak concentration of cyclic GMP at 2 min). Mytolon was the most effective of all cholinergic blockers tested. It was concluded that cyclic nucleotides may play a role in the modulatory process of the transmitters. A direct relation to the relaxation-contraction process could not be established.