ROLE OF YLAZOBENZYLOXYCARBONYL-L-PRO-L-LEU-GLY-L-PRO-D-ARG ACROSS RABBIT COLONIC SEGMENTS AND CACO-2 CELL MONOLAYERS( IN THE ASYMMETRIC PARACELLULAR TRANSPORT OF 4)

This study was conducted to demonstrate that Na+ played a role in the paracellular transport of ylazobenzyloxycarbonyl-L-Pro-L-Leu-Gly-L-Pro -D-Arg (Pz-peptide), a hydrophilic proline-containing pentapeptide, ac ross the rabbit colonic mucosa and Caco-2 cell monolayers. Over the 1 to 5 mM concentration range, Pt-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 Pt-pept ide to lower the transepithelial electrical resistance of Caco-2 cell monolayers only from the mucosal side. Blockade of Na+ access to the a pically located amiloride-sensitive Na+ channel in the lower intestina l segments by mucosal 10 mu M amiloride, serosal 100 mu M ouabain or r emoval of Na+ ions in the mucosal fluid dramatically reduced Pt-peptid e transport to 5% of the control. Moreover, Pt-peptide transport acros s Caco-2 cell monolayers could be titrated against mucosal Na+ concent ration. There was a small mucosal-to-serosal solvent drag effect induc ed by transepithelial Na+ flux stimulated by Pt-peptide in the colon, contributing in part to enhanced paracellular solute transport. Overal l, the above findings are consistent with a scenario whereby Pt-peptid e stimulates transepithelial Nat flux across the colonic segments at t he level of the amiloride-sensitive Naf channel, thereby triggering ye t to be identified intracellular biochemical changes that ultimately r esult in tight junctional opening and enhanced paracellular solute tra nsport.