FMRFamide and the related tetrapeptide FLRFamide are highly excitatory in molluscan non-cardiac smooth muscle. They are also exceptionally excitatory in the atrium and internally perfused ventricle of Busycon canaliculatum. These two peptides, usually thought of as classic molluscan cardio-acceleratory agents are in fact simply two members of a large and ever growing superfamily, the RFamide family, whose phylogenetic distribution has been so elegantly mapped by Walker . Members of this family, often with extended peptide chains (e.g. penta, hepta and decapeptides), stretch in their known distribution from the cnidaria to the chordates. The effects of some of the members of this superfamily (FMRFamide, FLRFamide, YMRFamide, TNRNFLRFamide, SDPFLRFamide, LMS) were examined. The neuropeptides were found to be very potent at very low concentrations (10–9 M) in the ventricle of both Buccinum and Busycon. Other neuropeptides (HFMRdFamide, SCPb, NLERFamide and pEGRFamide) were found to be without any effect. The Ca2+ dependency of these neuropeptides was also tested. The peptides appear to induce contraction of the ventricles by release of Ca2+ from internal pools. The neuropeptides appear to stimulate contraction in these cardiac muscles through a completely different pathway to Serotonin (the main excitatory neurotransmitter for the cardiac muscle). When the peptides were applied together with Serotonin an additive effect was observed clearly indicating the release of Ca2+ through different pathways. The nature of the RFamide receptor was also tested. It appears that the RFamide neuropeptides mobilize the 2nd messenger IP3 (Inositol trisphosphate), since the IP3 blocker Neomycin Sulphate inhibited the response of the neuropeptides.
Brooks, D. D. (1982) Membrane currents associated with contraction in molluscan visceral muscle. PhD Thesis, University of Lancaster, U.K.
Greenberg, M. J., Price, D. A. (1979) FMRFamide, a cardioexcitatory neuropeptide of molluscs. An agent in search of a mission. Am. Zool. 19, 163–174.
Cottrell, G. A., Davies, N. W. (1987) Multiple receptor sites for a molluscan peptide (FMRFamide) and related peptides of Helix. J. Physiol. (Lond.) 382, 51–68.
Ellis, A. M. (1998) The physiology, structure and pharmacology of the heart of Buccinum undatum. Ph.D. Thesis, University of Lancaster.
Hill, R. B., Langton, P. D. (1988) Use of a sucrose gap apparatus to record electrical responses of gastropod radular protractor muscle to FMRFamide. Comp. Biochem. Physiol. C 90, 113–122.
Huddart, H., Nelson, I. D., Brooks, D. D., Hill, R. B. (1992) The calcium dependency of electrical and mechanical responses of the odontophore protractor muscle of Busycon canaliculatum. A sucrose gap study of calcium antagonist action. Comp. Biochem. Physiol. A 102, 299–305.
Huddart, H., Hill, R. B. (1996) Electrical and mechanical characteristics of the atrium of the whelk Busycon canaliculatum. Gen. Pharmacol. 27, 1247–1254.
Huddart, H., Hill, R. B. (1996) Modulatory mechanisms in the isolated internally perfused ventricle of the whelk Busycon canaliculatum. Gen. Pharmacol. 27, 809–818.
Huddart, H., Nelson, I. D., Brooks, D. D., Hill, R. B. (1992) Electrical and mechanical responses of the odontophore protractor muscle of Busycon canaliculatum: a sucrose-gap voltage clamp study. Comp. Biochem. Physiol1. 102C, 149–158.
Hunt, S. (1981) Molluscan visceral muscle fine structure. General structure and sarcolemmal organization in the smooth muscle of the intestinal wall of Buccinum undatum L. Tissue & Cell 13, 283–297.
Nelson, I. D., Huddart, H. (1994) Neuromodulation in molluscan smooth muscle: the action of 5-HT, FMRFamide and purine compounds. Gen. Pharmacol. 25, 539–552.
Price, D. A. (1986) Evolution of a molluscan cardioregulatory neuropeptide. Am. Zool. 26, 1007–1015.
Price, D. A., Greenberg, M. J. (1980) Pharmacology of the molluscan cardioexcitatory neuropeptide FMRFamide. Gen. Pharmacol. 11, 237–241.
Smith, P. J. S., Hill, R. B. (1986) Cardiac performance in response to loading pressures and perfusion with 5-hydroxytryptamine in the isolated heart of Busycon canaliculatum (Gastropoda, Prosobranchia). J Exp. Biol. 123, 243–253.
Smith, P. J. S., Hill, R. B. (1987) Modulation of output from an isolated gastropod heart: effects of acetylcholine and FMRFamide. J. Exp. Biol. 127, 105–120.
Walker, R. J. (1992) Neuroactive peptides with an RFamide or Famide carboxyl terminal. Comp. Biochem. Physiol. 102C, 213–222.
Presented at the 10th ISIN Symposium on Invertebrate Neurobiology, July 5–9, 2003, Tihany, Hungary.
About this article
Cite this article
Moulis, A. RFamide Neuropeptide Actions on the Molluscan Heart. BIOLOGIA FUTURA 55, 335–341 (2004). https://doi.org/10.1556/ABiol.55.2004.1-4.39
- Buccinum undatum
- Busycon canaliculatum
- Ca2+ dependency
- RFamide neuropeptides