Two Myomodulins Isolated from Central Nervous System of Northwest Pacific Sea Hare, Aplysia kurodai, and Their Activities on Other Mollusks

The central nervous system (CNS) of Aplysia is a fascinating source to identify and characterize neuropeptides and neurotransmitters because of offering many useful divergent and convergent neuronal aggregates. Here, two neuropeptides were isolated from the extract of CNS of the northwest pacific sea hare, Aplysia kurodai, using HPLC system for fractionation and the anterior byssus retractor muscle (ABRM) of the Mytilis edulis as the bioassay system. Purified peptides, myomodulin A (MMA) and E (MME), were determined by amino acid sequencing and molecular mass analysis. MMA showed a potentiating effect at 100 nM or lower, on the contrary, an inhibitory effect at higher doses from 100 nM on phasic contraction elicited by repetitive electrical stimulation on the ABRM of Mytilus. However, MME only inhibited phasic contraction with all examined concentrations. MME revealed 100 times more potent activity than that of MMA on the relaxing catch-tension of ABRM stimulated by acetylcholine. Both MMA and MME potently stimulated a response on the crop and penial retractor muscle of the African giant snail, Achatina fulica, compared with other known mollusks neuropeptides. These results suggest that MMA and MME may be broadly distributed in CNS of Aplysia to function a neuromodulatory role controlled via excitatory and inhibitory neurons, and may be involved in the digestive and reproductive activity in other mollusk.