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First published online November 27, 2009
Journal of Experimental Biology 212, 3961-3976 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.035741

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The peptide hormone pQDLDHVFLRFamide (crustacean myosuppressin) modulates the Homarus americanus cardiac neuromuscular system at multiple sites

J. S. Stevens¹, C. R. Cashman¹, C. M. Smith², K. M. Beale², D. W. Towle², A. E. Christie² and P. S. Dickinson^1,*

¹ Department of Biology, Bowdoin College, 6500 College Station, Brunswick, Maine 04011 USA
² Center for Marine Functional Genomics, Mount Desert Island Biological Laboratory, PO Box 35, Old Bar Harbor Road, Salisbury Cove, Maine 04672 USA

^* Author for correspondence (pdickins{at}bowdoin.edu)

Accepted 27 August 2009

pQDLDHVFLRFamide is a highly conserved crustacean neuropeptide with a structure that places it within the myosuppressin subfamily of the FMRFamide-like peptides. Despite its apparent ubiquitous conservation in decapod crustaceans, the paracrine and/or endocrine roles played by pQDLDHVFLRFamide remain largely unknown. We have examined the actions of this peptide on the cardiac neuromuscular system of the American lobster Homarus americanus using four preparations: the intact animal, the heart in vitro, the isolated cardiac ganglion (CG), and a stimulated heart muscle preparation. In the intact animal, injection of myosuppressin caused a decrease in heartbeat frequency. Perfusion of the in vitro heart with pQDLDHVFLRFamide elicited a decrease in the frequency and an increase in the amplitude of heart contractions. In the isolated CG, myosuppressin induced a hyperpolarization of the resting membrane potential of cardiac motor neurons and a decrease in the cycle frequency of their bursting. In the stimulated heart muscle preparation, pQDLDHVFLRFamide increased the amplitude of the induced contractions, suggesting that myosuppressin modulates not only the CG, but also peripheral sites. For at least the in vitro heart and the isolated CG, the effects of myosuppressin were dose-dependent (10^–9 to 10^–6 mol l^–1 tested), with threshold concentrations (10^–8–10^–7 mol l^–1) consistent with the peptide serving as a circulating hormone. Although cycle frequency, a parameter directly determined by the CG, consistently decreased when pQDLDHVFLRFamide was applied to all preparation types, the magnitudes of this decrease differed, suggesting the possibility that, because myosuppressin modulates the CG and the periphery, it also alters peripheral feedback to the CG.

Key words: cardiac ganglion (CG), FMRFamide-like peptide (FLP), heart, Homarus americanus, lobster, myosuppressin, neurohormone, neuropeptide

Abbreviations: CCAP, crustacean cardioactive peptide • CG, cardiac ganglion • CPG, central pattern generator • ESI-Q-TOF MS/MS, electrospray ionization quadrupole time-of-flight tandem mass spectrometry • EST, expressed sequence tag • Homam-CLDH, Homarus americanus calcitonin-like diuretic hormone • MALDI-FTMS, matrix assisted laser desorption/ionization Fourier transform mass spectrometry • NO, nitric oxide • NOS, nitric oxide synthase • P, 0.1 mol l^–1 sodium phosphate buffer • PO, pericardial organ • P-Triton, 0.1 mol l^–1 sodium phosphate buffer containing 0.3% Triton X-100

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