Small cardioactive peptide gene: structure, expression and mass spectrometric analysis reveals a complex pattern of co-transmitters in a snail feeding neuron

The small cardioactive peptides (SCPs) are an important group of neural cot ransmitters in molluscs where they are known to play both central and perip heral modulatory roles in the control of feeding behaviour. Here we show th at in the snail Lymnaea the SCP gene exists in one interrupted copy that pr oduces a single species of transcript which encodes a prepropeptide contain ing two structurally related SCPs SGYLAFPRMamide (SCPA) and pQNYLAFPRMamide (SCPB). In situ hybridization was used to localize expression specifically to the soma of several types of motoneurons in the feeding system of Lymna ea, including the giant B2 foregut motoneurons. The peptide content of indi vidual B2 cell bodies was analysed by matrix-assisted laser desorption/ioni zation mass spectrometry and the structures of the SCPs predicted from the cloned gene were confirmed in these cells by post-source decay fragmentatio n analysis. Identical stimulatory activity for the two SCP peptides was dem onstrated by their application to the isolated foregut, suggesting that the ir co-release from the B2 cells may play an important part in the co-modula tion of gut motility, together with acetylcholine and the myomodulin family of peptides.