The effects of the nematode peptide, KHEYLRFamide (AF2), on the somatic musculature of the parasitic nematodeAscaris suum

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Abstract
SUMMARY: AF2 is an endogenous RFamide-like peptide from the parasitic nematodeAscaris suum. The potent stimulatory effects of this peptide on the somatic musculature ofAscarisstrongly suggest that it may have an important role in the motornervous system. Here we have investigated the possibility that AF2 may elicit a stimulatory action onAscarismuscle by potentiating the actions of the excitatory cholinergic motornervous system either pre-synaptically, post-synaptically or both. Inin vitropharmacological experiments AF2 produced a dose-dependent increase in the frequency and amplitude of spontaneous contractions ofAscarismuscle strip which lasted for more than 1 h after a 3 min application of AF2 (10 nM–10µM;N= 7). In addition, AF2 (100 nM) potentiated the contraction elicited by ACh by 43 ± 9% (P< 0·01;N= 8). In electro-physiological recordings from muscle cells, AF2 (10–100 nM;N= 10) potentiated the amplitude of EJPs (excitatory junction potentials). For 100 nM AF2, the potentiation of the EJP was 218 ± 48% (N= 7;P< 0·01). This effect reversed after a wash of 10 min. AF2 did not potentiate the depolarization of the muscle cell elicited by bath applied ACh. These latter two observations are consistent with a presynaptic action of AF2. AF2 (10–100 nM) generated spontaneous muscle cell action potentials in previously quiescent cells. This effect took more than 1 h to wash out. These observations are discussed in terms of the paralysis ofAscaristhat is elicited by AF2.