Effects of cholinoceptor compounds on larval metamorphosis of the mussel Mytilus coruscus

The metamorphosis responses of mussel(Mytilus coruscus)larvae to cholinoceptor compounds were investigated through a series of bioassays in order to obtain the information on muscarinic and nicotinic cholinoceptor in mediating larval metamorphosis in this species.In the inducing effect of the agonist,pediveliger larvae were exposed to the test solution either in 24-h exposure bath or in continuous exposure throughout the experiment.In the inhibitive effect of the antagonist,pediveliger larvae were exposed to the test solution in the absence or presence of the agonist.In the 24 h exposure assays,carbamylmethylcholine induced larval metamorphosis at 10^-5 to 10^-4 mol/L concentrations,while acetylcholine showed no inducing activity.In continuous exposure assays,carbamylmethylcholine showed inducing activity at 10^-5 to 10^-4 mol/L concentrations,and acetylcholine induced larval metamorphosis at 10^-6 to 10^-4 mol/L concentrations.Nicotinic cholinoceptor antagonist hexamethonium bromide did not inhibit larval metamorphosis in the presence of carbamylmethylcholine or acetylcholine.In contrast,muscarinic cholinoceptor antagonist atropine,inhibited larval metamorphosis in the presence of carbamylmethylcholine.In addition,no larval mortality was observed at all test concentrations.Thus,carbamylmethylcholine and acetylcholine can be used as non-toxic and useful inducers of larval metamorphosis in this species,and can improve M.coruscus larval production for aquaculture.The present study provides a novel insight into the mechanism modulating the metamorphosis of larval of the mussel M.coruscus.