Second messengers mediating mechanical responses to the FaRP GYIRFamide inthe fluke Fasciola hepatica

Spontaneous phasic contractions recorded from isolated body strips of Fasci ola hepatica were increased in frequency and amplitude by GYIRFamide, an FM RFamide-related peptide (FaRP). Superfusion with guanosine 5'-O-(2-thiodiph osphate) (100 muM, n = 5) reduced the effects of GYIRFamide on both frequen cy (by 82%) and amplitude (by 75%). The adenylate cyclase inhibitor MDL-123 30A (25 mM) increased spontaneous activity. MDL-12330A completely inhibited the frequency response to GYIRFamide and reduced the amplitude response by 66% as measured relative to this elevated basal activity (n = 6). Inhibiti on of phospholipase C (PLC) with neomycin sulfate (1 mM) had no direct effe ct on activity but reduced the frequency response to GYIRFamide by 64% and the amplitude increase by 95% (n = 9). The protein kinase C (PKC) inhibitor chelerythrine chloride (10 muM) also reduced frequency and amplitude respo nses by 98 and 99%, respectively, without affecting basal contractility (n = 5). Phorbol 12-myristate 13-acetate, an activator of PKC, increased contr action frequency and amplitude (n 5 6). It was concluded that GYIRFamide st imulates mechanical activity in F. hepatica through a G protein, via a PLC- and PKC-dependent second messenger pathway.