Abstract
The objectives of this study were to determine mRNA expression of monocarboxylate transporters (MCT) and to evaluate intestinal transport of the MCT substrates γ-hydroxybutyrate (GHB) and d-lactate in human intestinal Caco-2 cells. The presence of mRNA for MCT1, 2, 3, and 4 was observed in Caco-2 cells. The uptake of both GHB and d-lactate in Caco-2 cells was demonstrated to be pH- and concentration-dependent and sodium-independent. The uptake of GHB and d-lactate was best described by a Michaelis-Menten equation with passive diffusion (GHB: Km = 17.6 ± 10.5 mM, Vmax = 17.3 ± 11.7 nmol/min/mg, and P = 0.38 ± 0.15 μl/min/mg; and d-lactate: Km = 6.0 ± 2.9 mM, Vmax = 35.0 ± 18.4 nmol/min/mg, and P = 1.3 ± 0.6 μl/min/mg). The uptake of GHB and d-lactate was significantly decreased by the known MCT inhibitor α-cyano-4-hydroxycinnamate and the MCT substrates GHB and d-lactate but not by the organic cation tetraethylammonium chloride. Directional flux studies with both GHB and d-lactate suggested the involvement of carrier-mediated transport with the permeability in the apical to basolateral direction higher than that in the basolateral to apical direction. These findings confirm the presence of MCT1–4 in Caco-2 cells and demonstrate GHB and d-lactate transport characteristics consistent with proton-dependent MCT-mediated transport.
Footnotes
This work was supported in part by the National Institutes of Health National Institute on Drug Abuse [Grant DA023223]. W.K.L. was supported in part by an Undergraduate Summer Fellowship, and M.A.F. was supported by a Graduate Fellowship from Pfizer Global Research and Development.
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
doi:10.1124/dmd.109.030775.
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ABBREVIATIONS:
- MCT
- monocarboxylate transporter
- GHB
- γ-hydroxybutyric acid
- XP13512
- (±)-1-([(α-isobutanoyloxyethoxy)carbonyl] aminomethyl)-1-cyclohexane acetic acid
- CHC
- α-cyano-4-hydroxycinnamate
- TEA
- tetraethylammonium chloride
- MES
- 2-(N-morpholino)ethanesulfonic acid
- RT-PCR
- reverse transcriptase-polymerase chain reaction
- AP
- apical
- BL
- basolateral
- SMCT
- sodium-coupled monocarboxylate transporter
- siRNA
- small interfering RNA.
- Received October 13, 2009.
- Accepted December 1, 2009.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
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