THE EFFECTS OF THE NEMATODE PEPTIDE, KHEYLRFAMIDE (AF2), ON THE SOMATIC MUSCULATURE OF THE PARASITIC NEMATODE ASCARIS-SUUM

AF2 is an endogenous RFamide-like peptide from the parasitic nematode Ascaris suum. The potent stimulatory effects of this peptide on the so matic musculature of Ascaris strongly suggest that it may have an impo rtant role in the motornervous system. Here we have investigated the p ossibility that AF2 may elicit a stimulatory action on Ascaris muscle by potentiating the actions of the excitatory cholinergic motornervous system either pre-synaptically, post-synaptically or both. In in vitr o pharmacological experiments AF2 produced a dose-dependent increase i n the frequency and amplitude of spontaneous contractions of Ascaris m uscle strip which lasted for more than 1 h after a 3 min application o f AF2 (10 nM-10 mu M; N = 7). In addition, AF2 (100 nM) potentiated th e contraction elicited by ACh by 43 +/- 9 % (P < 0.01; N = 8). In elec trophysiological recordings from muscle cells, AF2 (10-100 nM; N = 10) potentiated the amplitude of EJPs (excitatory junction potentials). F or 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 pote ntiate the depolarization of the muscle cell elicited by bath applied ACh. These latter two observations are consistent with a presynaptic a ction 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 para lysis of Ascaris that is elicited by AF2.