Inhibitory effects of nematode FMRFamide-related peptides (FaRPs) on muscle strips fromAscaris suum

Abstract

A large number of FMRFamide-related peptides (FaRPs) are found in nematodes, and some of these are known to influence tension and contractility of neuromuscular strips isolated from Ascaris suum body wall. Relaxation of these strips has been noted with five nematode FaRPs. The inhibitory actions of SDPNFLRFamide (PF1) and SADPNFLRFamide (PF2) appear to be mediated by nitric oxide, as previously demonstrated with inhibitors of nitric oxide synthase (NOS). This present study showed that the effects of PF1 were also depended on external Ca++ and were reduced by the Ca(++)-channel blocker verapamil, observations consistent with the finding that nematode NOS is Ca(++)-dependent. KSAYMRFamide (PF3), KNIRFamide (PF4) and KNAFIRFamide (an alanine substituted analog of KNEFIRFamide, AF1, termed A3AF1) also relaxed A. suum muscle strips, but these responses were not affected by NOS inhibitors. PF3 inhibited the activity of strips prepared from the dorsal side of the worm, but contracted ventral strips. Both effects were dependent on the presence of ventral/dorsal nerve cords (unlike PF1/PF2) and were attenuated in medium which contained high K+ or low Ca++. PF4-induced muscle relaxation and hyperpolarization were independent of nerve cords, but were reversed in Cl-free medium, unlike PF1 or PF3. The PF4 effect physiologically desensitized muscle strips to subsequent treatment with PF4 and/or GABA. However, PF4 and GABA were not synergistic in this preparation. The effects of GABA, but not PF4, were reduced in muscle strips treated with the GABA antagonist, NCS 281-93. Following PF4 (or GABA) relaxation, subsequent treatment with higher doses of PF4 caused muscle strip contraction. A3AF1 was found to relax muscle strips and hyperpolarize muscle cells independently of the ventral and dorsal nerve cords, K+, Ca++, and Cl-, and mimicked the inhibitory phase associated with the exposure of these strips to AF1. On the basis of anatomical and ionic dependence, these data have delineated at least four distinct inhibitory activities attributable to nematode FaRPs. Clearly, a remarkably complex set of inhibitory mechanisms operate in the nematode neuromuscular system.

The FMRFamide-Like Peptide Family in Nematodes

“…Data obtained from this type of studies do, however, not always facilitate a better understanding of in vivo physiological functions. Although an array of FLP peptides clearly shows muscle-based effects, denervation of somatic muscle strips can alter or even abolish the activity of many FLPs indicating that FLP-receptors do not only reside on muscles (1, 92). Electrophysiological studies indeed demonstrate that FLPs, such as AF1, can act through modulation of neuronal conductance of motor neurons in addition to their muscle-based effects (137).…”

A review of FMRFamide- and RFamide-like peptides in metazoa

“…Maule et al have also conducted extensive studies on the bioactivity of FLPs (Maule et al , 1996Mousley et al 2005). The PF FLPs identified in Panagrellus redivivus are of particular interest (Geary et al 1992;Maule et al 1995). Four PF FLPs have been identified in P. redivivus, viz, PF1 (SDPNFLRFa), PF2 (SADPNFLRFa), PF3 (KSAYMRFa) and PF4 (KPNFIRFa).…”

Isolation and Preliminary Biological Assessment of AADGAPLIRFamide and SVPGVLRFamide from Caenorhabditis elegans

“…Thus, Cl Ϫ ions are likely to be involved in the inhibitory mechanism induced by the peptide. Cl Ϫ ions have been implicated in the inhibitory response of another FaRP of free-living nematode origin, PF4 (KPNFIRFamide) (3,26). However, a feature of the PF4 effect on A. suum somatic muscle is the rapid relaxation and subsequent recovery phase.…”

“…FaRPs have been isolated from both free-living and parasitic species of the phylum Nematoda and are now recognised as important signalling molecules within the nervous system of this invertebrate group, eliciting potent neuromodulatory effects (3)(4)(5). For instance, flp-1 gene knockout revealed multiple phenotypic changes in Caenorhabditis elegans (6).…”