title: Role of Na+ in the asymmetric paracellular transport of 4-phenylazobenzyloxycarbonyl-L-Pro-L-Leu-Gly-L-Pro-D-Arg across rabbit colonic segments and Caco-2 cell monolayers.
abstract: This study was conducted to demonstrate that Na+ played a role in the paracellular transport of 4-phenylazobenzyloxycarbonyl-L-Pro-L-Leu-Gly-L-Pro-D-Arg (Pz-peptide), a hydrophilic proline-containing pentapeptide, across the rabbit colonic mucosa and Caco-2 cell monolayers. Over the 1 to 5 mM concentration range, Pz-peptide transport was 25 to 180 times greater from the mucosal-to-serosal than from the opposite direction. This asymmetry in transport was consistent with the ability of Pz-peptide to lower the transepithelial electrical resistance of Caco-2 cell monolayers only from the mucosal side. Blockade of Na+ access to the apically located amiloride-sensitive Na+ channel in the lower intestinal segments by mucosal 10 microM amiloride, serosal 100 microM ouabain or removal of Na+ ions in the mucosal fluid dramatically reduced Pz-peptide transport to 5% of the control. Moreover, Pz-peptide transport across Caco-2 cell monolayers could be titrated against mucosal Na+ concentration. There was a small mucosal-to-serosal solvent drag effect induced by transepithelial Na+ flux stimulated by Pz-peptide in the colon, contributing in part to enhanced paracellular solute transport. Overall, the above findings are consistent with a scenario whereby Pz-peptide stimulates transepithelial Na+ flux across the colonic segments at the level of the amiloride-sensitive Na+ channel, thereby triggering yet to be identified intracellular biochemical changes that ultimately result in tight junctional opening and enhanced paracellular solute transport.
authors.affiliation: University of Southern California, School of Pharmacy, Department of Pharmaceutical Sciences, Los Angeles.
authors.forename: W C
authors.initials: WC
authors.lastname: Yen
authors.forename: V H
authors.initials: VH
authors.lastname: Lee
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D018938:Caco-2 Cells / Q000378:metabolism*; D002712:Chlorides / Q000502:physiology; D003106:Colon / Q000378:metabolism*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000502:physiology*; D011817:Rabbits; D012964:Sodium / Q000502:physiology*; D015222:Sodium Channels / Q000378:metabolism
chemical_list: D002712:Chlorides; D009842:Oligopeptides; D015222:Sodium Channels; C043091:PZ-peptide; D000584:Amiloride; D012964:Sodium