BIOACTIVITY OF FMRFAMIDE AND RELATED PEPTIDES ON A CONTRACTILE SYSTEM OF THE COELENTERATE RENILLA-KOLLIKERI

The pharmacological activity of peptides terminating with RFamide was investigated in the rachidial tissue of the colonial anthozoan Renilla kollikeri. FMRFamide and RFamide induced tonic rachidial contractions in a dose-dependent manner, the threshold concentration being 0.1 .mu.M. This response was elicited to a lesser extent by FLRFamide and abolished in the presence of an antibody to FMRFamide. Colonial activities coordinated by the through-conducting nerve-net of Renilla such as stimulation-induced luminescence and rachidial contractions were enhanced in the presence of FMRFamide. FMRFamide-induced tonic contractions were independent of external calcium or sodium, were not influenced by adding lanthanum or cobalt to the bathing medium, but were blocked by D600 and verapamil. Contrary to the peptide-elicited tonic contraction, rhythmic and electrically stimulated rachidial contractions were dependent on external calcium, thus demonstrating that the ionic mechanisms associated with these agents differ from those involved with the FMRFamide response. This and other (immunohistochemical) evidence suggest that a FmRFamide-related peptide plays a role in neuromuscular transmission in Renilla.