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The Journal of Experimental Biology 204, 3019-3026 (2001)
© 2001 The Company of Biologists Limited

Glucagon-like peptide isolated from the eel intestine: effects on atrial beating

Toshihiro Uesaka^1,3, Keiichi Yano², Seiji Sugimoto² and Masaaki Ando^1,*

¹ Laboratory of Integrative Physiology, Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739-8521, Japan,
² Tokyo Research Laboratories, Kyowa Hakko Kogyo Co. Ltd, 3-6-6 Asahimachi, Machidashi, Tokyo 194-0023, Japan and
³ Department of Environment and Mutation, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima 734-8553, Japan

*Author for correspondence (e-mail: mando{at}hiroshima-u.ac.jp)

Accepted June 13, 2001

A new glucagon-like peptide was isolated from the intestine of the eel Anguilla japonica. The primary structure was determined by sequence analysis after cleavage with lysyl endopeptidase, quantitative amino acid analysis and fast atom bombardment mass spectrometry as HSQGTFTNDY¹⁰SKYLETRRAQ²⁰DFVQWLMNSK³⁰RSGGPT. Since its structure is similar to that of oxyntomodulins (OXMs) reported in various vertebrates, we named this peptide eel oxyntomodulin (eOXM). We found that eOXM enhanced the contractile force and the beating rate of the eel atrium in a dose-dependent manner. These effects of eOXM were not inhibited by betaxolol, a ß₁-adrenoceptor antagonist, indicating that the actions of eOXM were independent of those of adrenaline. eOXM enhanced the intracellular Ca²⁺ concentration of the myocardium. The contractility of the eel atrium was greatly reduced after omitting Ca²⁺ from the bathing medium or after treatment with verapamil, a Ca²⁺ channel blocker. After inhibiting Ca²⁺ entry under these conditions, the inotropic effect of eOXM was markedly reduced, but the chronotropic effect was not altered significantly. These results indicate that the inotropic effect of eOXM is via a stimulation of Ca²⁺ influx but that the chronotropic effect may be independent of extracellular Ca²⁺.

Key words: eel, oxyntomodulin, intestine, atrial beating, intracellular Ca²⁺, extracellular Ca²⁺, Anguilla japonica.

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