Effects of eel neuropeptide Y on ion transport across the seawater eel intestine

A neuropeptide Y (eNPY) was isolated from the intestinal extract of eels. This peptide enhanced significantly the serosa-negative transepithelial potential difference (PD) and short-circuit current (Isc) across the intestine of the seawater eel after pretreatment with isobutylmethylxanthine, serotonin and methacholine. The effects of eNPY on the Isc were concentration-dependent with a threshold concentration of 3 x 10(-9) M and a maximal effect at 3 x 10(-7) M. Similar concentration-response curve was obtained by porcine peptide YY (pPYY). Since 9 amino acid residues are replaced in the pPYY, this result indicates that these substitutions do not change the potency and the efficacy. These stimulatory actions of eNPY were not blocked by tetrodotoxin, an inhibitor of neural firing, or yohimbine, an alpha 2-adrenoceptor antagonist, indicating that eNPY acts without enteric neural firing or catecholamine release. When eNPY and adrenaline (AD) were applied simultaneously, the effects were additive only at lower dosage (3 x 10(-8) M for eNPY, 3 x 10(-8) M for AD), but not at high dosage (10(-6) M eNPY, 10(-7) M AD). The ceiling effect at high dosage suggests that these two regulators act through common signal transduction systems and affect the Na(+)-K(+)-Cl- cotransport system, since both effects were completely blocked by bumetanide, a specific inhibitor of Na(+)-K(+)-Cl- cotransporter.