Arthropod FMRFamide-related peptides modulate muscle activity in helminths.

FMRFamide-related peptides are common to a wide variety of invertebrate species, including helminths and arthropods. In arthropods, five distinct FMRFamide-related peptide subfamilies are recognised: the myosuppressins, extended-FLRFamides, -FMRFamides, -RFamides, and sulfakinins, members of which induce potent and diverse myotropic effects. Whilst >80 FMRFamide-related peptides have been identified in nematodes, only four FMRFamide-related peptides have been characterised from flatworms. The Ascaris suum ovijector/body wall bioassay and the Procerodes littoralis muscle fibre bioassay have proved both reliable and sensitive systems for assessing the functional activities of FMRFamide-related peptides in vitro, and data describing the effects of native FMRFamide-related peptides in these systems are rapidly accumulating. This is the first study to determine the cross-phyla activities of non-native FMRFamide-related peptides in both nematode and flatworm species. In the present study, the effects of 10 arthropod FMRFamide-related peptides (leucomyosuppressin [pQDVDHVFLRFamide], schistoFLRFamide [PDVDHVFLRFamide] and truncated analogues [HVFLRFamide and VFLRFamide], lobster peptide I [TNRNFLRFamide], lobster peptide II [SDRNFLRFamide], manducaFLRFamide II [GNSFLRFamide], manducaFLRFamide III [DPSFLRFamide], calliFMRFamide 4 [KPNQDFMRFamide] and perisulfakinin [EQFDDY(SO(3)H)GHMRFamide]), representing the five subfamilies, were examined on the body wall and ovijector of the parasitic porcine nematode, A. suum and dispersed muscle fibres from the free-living turbellarian, P. littoralis. The muscle activity of the ovijector was found to be modulated significantly by each of the arthropod FMRFamide-related peptides tested; the effects were concentration-dependent, reversible and repeatable. All but one (perisulfakinin) of the 10 arthropod FMRFamide-related peptides examined modulated significantly the activity of A. suum body wall muscle. In addition, all of the arthropod FMRFamide-related peptides examined induced potent concentration-dependent contractions of P. littoralis muscle fibres. These results reveal similarities in the ligand requirement(s) between FMRFamide-related peptide receptors within the Phyla Arthropoda, Nematoda and Platyhelminthes, and indicate significant receptor promiscuity, which highlights the potential of FMRFamide-related peptide receptors as legitimate targets for novel endectocidal agents.