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First published online June 15, 2007
Journal of Experimental Biology 210, 2278-2289 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.004770

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Identification and cardiotropic actions of sulfakinin peptides in the American lobster Homarus americanus

Patsy S. Dickinson^1,*, Jake S. Stevens¹, Szymon Rus¹, Henry R. Brennan¹, Christopher C. Goiney², Christine M. Smith³, Lingjun Li^4,5, David W. Towle³ and Andrew E. Christie^2,3

¹ Department of Biology, Bowdoin College, 6500 College Station, Brunswick, ME 04011, USA
² Department of Biology, University of Washington, Box 351800, Seattle, WA 98195-1800, USA
³ Mount Desert Island Biological Laboratory, PO Box 35, Old Bar Harbor Road, Salisbury Cove, ME 04672, USA
⁴ School of Pharmacy, University of Wisconsin, 777 Highland Avenue, Madison, WI 53705-2222, USA
⁵ Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, WI 53706-1396, USA

^* Author for correspondence (e-mails: pdickins{at}bowdoin.edu)

Accepted 3 April 2007

In arthropods, a group of peptides possessing a –Y_(SO3H)GHM/LRFamide carboxy-terminal motif have been collectively termed the sulfakinins. Sulfakinin isoforms have been identified from numerous insect species. In contrast, members of this peptide family have thus far been isolated from just two crustaceans, the penaeid shrimp Penaeus monodon and Litopenaeus vannamei. Here, we report the identification of a cDNA encoding prepro-sulfakinin from the American lobster Homarus americanus. Two sulfakinin-like sequences were identified within the open-reading frame of the cDNA. Based on modifications predicted by peptide modeling programs, and on homology to the known isoforms of sulfakinin, particularly those from shrimp, the mature H. americanus sulfakinins were hypothesized to be pEFDEY_(SO3H)GHMRFamide (Hoa-SK I) and GGGEY_(SO3H)DDY_(SO3H)GHLRFamide (Hoa-SK II). Hoa-SK I is identical to one of the previously identified shrimp sulfakinins, while Hoa-SK II is a novel isoform. Exogenous application of either synthetic Hoa-SK I or Hoa-SK II to the isolated lobster heart increased both the frequency and amplitude of spontaneous heart contractions. In preparations in which spontaneous contractions were irregular, both peptides increased the regularity of the heartbeat. Our study provides the first molecular characterization of a sulfakinin-encoding cDNA from a crustacean, as well as the first demonstration of bioactivity for native sulfakinins in this group of arthropods.

Key words: cDNA, neurohormone, pEFDEY_(SO3H)GHMRFamide, GGGEY_(SO3H)DDY_(SO3H)GHLRFamide, heart, sulfakinin, Homarus americanus, expressed sequence tag (EST), neuromodulation, cardiac ganglion

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