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

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 HSQGTFTNDY(10)SKYLETRRAQ(20)DFVQWLMNSK(30)RSGGPT. 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 beta(1)-adrenoceptor antagonist, indicating that the actions of eOXM were independent of those of adrenaline. eOXM enhanced the intracellular Ca(2+) concentration of the myocardium. The contractility of the eel atrium was greatly reduced after omitting Ca(2+) from the bathing medium or after treatment with verapamil, a Ca(2+) channel blocker. After inhibiting Ca(2+) 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 Ca(2+) influx but that the chronotropic effect may be independent of extracellular Ca(2+).