Dipeptide transport in brush-border membrane vesicles (BBMV) prepared from human full-term placentae.
The uptakes of the tritiated, hydrolysis-resistant cationic (d-Phe-L-Lys), neutral (D-Phe-L-Ala) and anionic (D-Phe-L-Glu) peptides into human full-term placental brush-border membrane vesicles (BBMV) were time-dependent and into an osmotically-active space. Uptakes of D-Phe-L-Lys and D-Phe-L-Glu were temperature-dependent. Uptake of D-Phe-L-Lys was electroneutral (either cation exchange or anion co-transport), whereas D-Phe-L-Ala and D-Phe-L-Glu were both stimulated by an increasingly inside-positive membrane potential (explained by either cation exchange or anion co-transport, or translocation alone, respectively). Uptake of D-Phe-L-Ala was stimulated (approximately 50 per cent) by an inwardly-directed proton gradient (pHin = 7.4, pHout = 5.5), whereas D-Phe-L-Glu was unaffected, and D-Phe-L-Lys uptake was inhibited (approximately 50 per cent) but was unaffected by the organic cation-exchange inhibitors 1,1-diethyl-2,2-cyanine (decynium22) and 5-(N-methyl-N-isobutyl)amiloride (MIBA). Over the concentration range studies, the peptides did not self-inhibit, and the only cross-inhibition was by D-Phe-L-Glu on D-Phe-L-Lys uptake (estimated K(I) 24.2 +/- 1.36 mM), suggesting very low affinity transporter(s). Under conditions favouring its transport by PepT1, D-Phe-L-Glu uptake was unaffected by diethylpyrocarbonate (DEPC); neither D-Phe-L-Ala nor D-Phe-L-Lys was inhibited by DEPC under maximally proton-stimulated conditions of uptake. We conclude that Pep-T-like transporters are not responsible for peptide uptake into human placental BBMV; while the molecular identity of the transporter(s) involved remains unclear, we hypothesize that they could be similar to the as yet unidentified epithelial basolateral peptide transporter(s).
Meredith
D
D
Department of Human Anatomy, University of Oxford, UK.
Laynes
R W
RW
D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D001692:Biological Transport; D004047:Diethyl Pyrocarbonate / Q000494:pharmacology; D004151:Dipeptides / Q000493:pharmacokinetics*; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000502:physiology; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism*; D017830:Octoxynol / Q000494:pharmacology; D009994:Osmolar Concentration; D010920:Placenta / Q000187:drug effects / Q000502:physiology*; D011247:Pregnancy / Q000502:physiology*; D013696:Temperature
D004151:Dipeptides; D000584:Amiloride; D017830:Octoxynol; C056369:5-(N-methyl-N-isobutyl)amiloride; D004047:Diethyl Pyrocarbonate