The role of cAMP in the actions of the peptide AF3 in the parasitic nematodes Ascaris suum and Ascaridia galli

AF3 (AVPGVLRFamide) is an endogenous RFamide-like peptide isolated from the parasitic nematode Ascaris suum. It has a potent and long lasting excitatory effect in A. suum and Ascaridia galli. This is mediated by a mechanism independent of the nicotinic-like acetylcholine (ACh) receptor, which mediates excitatory transmission at the neuromuscular junction of both nematodes. In addition, AF3 has been found to sensitise A. suum muscle to the contractile effect of ACh. In this study, the involvement of the second messenger cAMP in mediating the action of AF3 on the somatic musculature of A. suum and A. galli has been investigated. Two approaches have been used; the effects of drugs which raise intracellular cAMP levels on the contractile responses to AF3 have been examined and biochemical assays have been used to measure the effects of AF3 on cAMP levels. AF3 contractions were inhibited in A. suum by 10 μM forskolin (by 22% of control; P