title: Direct assessment of dipeptide/H+ symport in intact human intestinal (Caco-2) epithelium: a novel method utilising continuous intracellular pH measurement.
abstract: Direct demonstration of intact peptide transport by the intestinal H+/dipeptide carrier is limited both by luminal/cytosolic hydrolysis and the availability of suitable radiolabelled substrates. Perfusion of Val-Val (20mM) at the apical surface of human intestinal epithelial (Caco-2) cell monolayers resulted in a marked intracellular acidification, due to dipeptide-induced H(+)-flow across the apical membrane. Val-Val (20mM) also inhibited both the pH-dependent apical-to-basal transport and intracellular accumulation of [14C]Gly-Sar. Valine (20mM) had no effect on [14C]Gly-Sar transport (and intracellular accumulation) or pHi. We conclude that this novel method for studying H(+)-coupled transport clearly differentiates between the mechanisms responsible for absorption of an intact substrate and products of hydrolysis.
authors.affiliation: Department of Physiological Sciences, University of Newcastle upon Tyne, Medical School, Newcastle upon Tyne, U.K.
authors.forename: D T
authors.initials: DT
authors.lastname: Thwaites
authors.forename: B H
authors.initials: BH
authors.lastname: Hirst
authors.forename: N L
authors.initials: NL
authors.lastname: Simmons
mesh_terms: D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003110:Colonic Neoplasms; D004151:Dipeptides / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007422:Intestines; D007700:Kinetics; D000074011:Peptide Transporter 1; D027981:Symporters; D014407:Tumor Cells, Cultured; D014633:Valine / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D004151:Dipeptides; D000074011:Peptide Transporter 1; C082186:SLC15A1 protein, human; D027981:Symporters; C004194:glycylsarcosine; C034792:valylvaline; D014633:Valine