PT  - JOURNAL ARTICLE
AU  - Wing Ki Lam
AU  - Melanie A. Felmlee
AU  - Marilyn E. Morris
TI  - Monocarboxylate Transporter-Mediated Transport of γ-Hydroxybutyric Acid in Human Intestinal Caco-2 Cells
AID  - 10.1124/dmd.109.030775
DP  - 2010 Mar 01
TA  - Drug Metabolism and Disposition
PG  - 441--447
VI  - 38
IP  - 3
4099  - http://dmd.aspetjournals.org/content/38/3/441.short
4100  - http://dmd.aspetjournals.org/content/38/3/441.full
SO  - Drug Metab Dispos2010 Mar 01; 38
AB  - 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. Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics