Somatostatin-related peptides isolated from the eel gut: effects on ion and water absorption across the intestine of the seawater eel.
Four somatostatin-related peptides were isolated from eel guts. Two of them were the same as eel SS-25II (eSS-25II) and eel SS-25I (eSS-25I) isolated from European eel pancreas. The remaining two peptides were C-terminal tetradecapeptides (eSS-14II and eSS-14I) of eSS-25II and eSS-25I, respectively. These four peptides all enhanced the serosa-negative transepithelial potential difference and short-circuit current across the seawater eel intestine after pretreatment with isobutylmethylxanthine, serotonin (5-HT) and methacholine, an agonist of acetylcholine (ACh). Among these peptides, eSS-25II was the most potent enhancer, followed by eSS-25I and eSS-14II. Since the large peptide (eSS-25II) acts at a lower concentration than the small somatostatin (eSS-14II), the 11 N-terminal amino acid residues seem to potentiate somatostatin action in the eel intestine. In contrast, eSS-14II was more potent than mammalian SS-14, indicating that the three amino acid residues (Tyr18, Gly21, Pro22) in the C-terminal portion also contribute to the potency of somatostatin. Endogenous somatostatin (eSS-25II) activated net Na+, Cl- and water fluxes across the seawater eel intestine. This stimulatory action was not inhibited by tetrodotoxin or yohimbine, an adrenergic antagonist, indicating that eSS-25II does not act through neuronal firing or through catecholamine release. Thus, eel somatostatins may act directly on the enterocytes, but on a distinct receptor from that for adrenaline, to antagonize the inhibition of NaCl and water absorption by 5-HT and ACh in the seawater eel intestine.
Uesaka
T
T
Laboratory of Physiology, Faculty of Integrated Arts and Sciences, Hiroshima University, Japan.
Yano
K
K
Yamasaki
M
M
Nagashima
K
K
Ando
M
M
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000109:Acetylcholine / Q000494:pharmacology; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000811:Anguilla / Q000502:physiology*; D000818:Animals; D004064:Digestive System / Q000737:chemistry; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects; D017136:Ion Transport / Q000187:drug effects; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000302:isolation & purification* / Q000494:pharmacology; D017386:Sequence Homology, Amino Acid; D012701:Serotonin / Q000494:pharmacology; D013004:Somatostatin / Q000031:analogs & derivatives* / Q000302:isolation & purification / Q000494:pharmacology; D014867:Water / Q000378:metabolism; D015016:Yohimbine / Q000494:pharmacology
D000596:Amino Acids; D010455:Peptides; D014867:Water; D015016:Yohimbine; D012701:Serotonin; D013004:Somatostatin; D000109:Acetylcholine; D015056:1-Methyl-3-isobutylxanthine