The effect of the nematode peptides SDPNFLRFamide (PF1) and SADPNFLRFamide (PF2) on synaptic transmission in the parasitic nematodeAscaris suum

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Abstract
SUMMARY: The action of two peptides isolated from the nematodePanagrellus redivivus, PF1 (SDPNFLRFamide) and PF2 (SADPNFLRFamide) have been studied on synaptic transmission in the motornervous system of the parasitic nematodeAscaris suum.Intracellular recordings were made fromAscarissomatic muscle cells and excitatory junction potentials (EJPs) elicited by stimulation of the ventral nerve cord. The EJPs were cholinergic as they were blocked by theAscarisnicotinic receptor antagonist, benzoquinonium. PF1 caused a slow hyperpolarization, similar to the action of this peptide first reported by Bowman, Geary & Thompson (1990) and further characterized by Frankset al.(1994). The hyper-polarization was accompanied by a marked decrease in the amplitude of the EJPs with an EC50of 311 ± 30 nM (n= 5). This inhibition is unlikely to be due to a post-synaptic site of action of the peptide as the muscle cell input conductance was not significantly altered by PF1 and furthermore the response to bath-applied acetylcholine was not inhibited by PF1 at concentrations up to 10μM (n= 6). PF2 also inhibited the EJPs in a similar manner to PF1. These studies indicate that both of the peptides isolated from the free-living nematodePanagrellus redivivushave biological activity in the parasitic nematodeAscaris suum. PF1 and PF2 have inhibitory actions in contrast to the predominantly excitatory actions of theAscarisendogenous peptides AF1 (KNEFIRFamide) and AF2 (KHEYLRFamide). The potent actions of thePanagrellusneuropeptides PF1 and PF2 inAscarissuggest that peptides with a similar or identical sequence may also occur inAscarisand have an inhibitory role in the motornervous system.