Meeting Abstract
FMRFamide modifies muscular activity of the crop-gizzard in the earthworm, Lumbricus terrestris and therefore we decided to examine the effects of FMRFamide-related peptides (FaRPs) on the isolated intestine. After removing 6-8 mm of intestinal tissue, the sample was suspended in a saline solution and connected to a Grass force transducer. The contractions were allowed to stabilize and recording on a computer using iWorx software. Increasing concentrations of peptide were added to the bath and the response were used to construct log concentration response curves for the change in amplitude and frequency. FMRFamide had an excitatory effect on both the amplitude and frequency with a threshold of 10-6 M. APKQYVRFamide, which is native to the genus Lumbricus, elicited an excitatory effect in both amplitude and frequency at 10-9 M, while increasing concentrations inhibited these variables until they returned to the baseline. PAKHYVRFamide, an annelid FaRP, caused an increase in amplitude with a threshold of 10-6 M with little effect on the rate. To explore the roles of valine (V) and tyrosine (Y) in the C-terminal tetrapeptide we also examined the effects of FVRFamide and YVRFamide. At 10-9 M FVRFamide caused an increase in amplitude and at 10-8 M a decrease. It also caused an increase in rate with a threshold of 10-7 M and a decrease at 10-6 M. YVRFamide caused an increase in amplitude with a threshold of 10-5 M and a decrease in rate with a threshold of 10-7 M. These data suggest that FMRFamide and APKQYVRFamide may be working on different receptors. The responses to PAKHYVRFamide and the tetrapeptides suggest that these differences may be due to more than just the tyrosine and valine substitutions in the C-terminal.
