Meeting Abstract
FMRFamide-related peptides are found in most animals, however the authentic FMRFamide along with YMRFamides are found in only molluscs and annelid. Annelids also have YVRFamides. Since FMRFamide excites the heart of the clam Mercenaria mercenaria, we decided to see if annelid peptides did the same. For this study we used FMRFamide, FVRFamide, YMRFamide, YVRFamide, AYVRFamide and QYVRFamide. Hearts were placed in a tissue bath of artificial seawater. Contractions were recorded with a force transducer and computer as increasing concentrations of peptide were added to the bath. The data were used to construct log concentration response curves for rate and amplitude changes. FMRFamide stimulated rate (threshold 0.1 μM) and amplitude (threshold 1 μM). FVRFamide caused a small rise in amplitude and rate (threshold 1 μM). YMRFamide caused a small rise in amplitude (threshold 1 μM). YVRFamide stimulated rate (threshold 10 μM) and amplitude (threshold 1 μM). AYVRFamide and QYVRFamide inhibited amplitude (threshold 0.1 μM). The order of potency for the tetrapeptides was FMRFamide > FVRFamide > YMRFamide > YVRFamide indicating that the receptor requires phenylalanine in the N-terminal to a greater extent than it needs methionine in the second position for full efficacy. The extended YVRFamides were inhibitory. The addition of either alanine or glutamine to the N-terminal caused the excitatory YVRFamide to become inhibitory suggesting that the receptor cannot bind the pentapeptide and activate the transduction pathway. The inhibition caused by the pentapeptides suggest that the peptides might be acting as an antagonist to the clam receptor by blocking the effects of any FMRFamide that may be released from the cardiac nerves that are still present in the isolated heart.
