title: Dual modes of 5-(N-ethyl-N-isopropyl)amiloride modulation of apical dipeptide uptake in the human small intestinal epithelial cell line Caco-2.
abstract: Selective pharmacological Na+/H+ exchange (NHE) inhibitors were used to identify functional NHE isoforms in human small intestinal enterocytes (Caco-2) and to distinguish between direct and indirect effects on transport via the intestinal di/tripeptide transporter hPepT1. The relative potencies of these inhibitors to inhibit 22Na+ influx identifies NHE3 and NHE1 as the apical and basolateral NHE isoforms. The Na+-dependent (NHE3-sensitive) component of apical dipeptide ([14C] Gly-Sar) uptake was inhibited by the selective NHE inhibitors with the same order of potency observed for inhibition of apical 22Na+ uptake. However, 5-(N-ethyl-N-isopropyl) amiloride (EIPA) also reduced [14C]Gly-Sar uptake in the absence of Na+ and this inhibition was concentration and pH (maximal at pH 5.5) dependent. NHE3 inhibition by S1611 and S3226 modulates dipeptide uptake indirectly by reducing the transapical driving force (H+ electrochemical gradient). EIPA (at 100 microM) has similar effects, but at higher concentrations (> 200 microM) also has direct inhibitory effects on hPepT1.
authors.affiliation: Institute for Cell & Molecular Biosciences, Faculty of Medical Sciences, University of Newcastle upon Tyne, Newcastle upon Tyne, NE2 4HH, UK.
authors.forename: D J
authors.initials: DJ
authors.lastname: Kennedy
authors.forename: D
authors.initials: D
authors.lastname: Raldua
authors.forename: D T
authors.initials: DT
authors.lastname: Thwaites
mesh_terms: D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000704:Analysis of Variance; D001692:Biological Transport / Q000187:drug effects; D018938:Caco-2 Cells; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D004151:Dipeptides / Q000493:pharmacokinetics*; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D006146:Guanidines / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007421:Intestine, Small / Q000378:metabolism / Q000473:pathology; D008564:Membrane Potentials / Q000187:drug effects; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D008689:Methacrylates / Q000494:pharmacology; D000074011:Peptide Transporter 1; D020033:Protein Isoforms / Q000378:metabolism; D011522:Protons; D012964:Sodium / Q000378:metabolism; D000074082:Sodium-Hydrogen Exchanger 1; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000378:metabolism; D013450:Sulfones / Q000494:pharmacology; D027981:Symporters / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: C118956:3-(2-(3-guanidino-2-methyl-3-oxo-propenyl)-5-methylphenyl)-N-isopropylidene-2-methyl-acrylamide dihydrochloride; D027682:Cation Transport Proteins; D004151:Dipeptides; D006146:Guanidines; D008565:Membrane Proteins; D008689:Methacrylates; D000074011:Peptide Transporter 1; D020033:Protein Isoforms; D011522:Protons; C082186:SLC15A1 protein, human; C490998:SLC9A1 protein, human; C000613385:SLC9A3 protein, human; D000074082:Sodium-Hydrogen Exchanger 1; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; D027981:Symporters; D000584:Amiloride; C093373:cariporide; D012964:Sodium; C039614:ethylisopropylamiloride