ABSTRACT:The objectives of this study were to determine mRNA expression of monocarboxylate transporters (MCT) and to evaluate intestinal transport of the MCT substrates ␥-hydroxybutyrate (

PurposeTo evaluate the expression of monocarboxylate transporters (MCTs) 1‐4 and characterize the intestinal transport of the known MCT substrates, γ‐hydroxybutyric acid (GHB) and D‐lactate.MethodsThe mRNA and protein expression of MCT1‐4 were determined by RT‐PCR and western blotting. GHB and D‐lactate uptake and directional flux kinetics were analyzed in Caco‐2 cells. Transport properties were determined with specific inhibitors and different pH and sodium conditions.ResultsMCT1‐4 mRNA was expressed in Caco‐2 cells; however, protein expression was observed for only MCT1, 2 and 4. GHB and D‐lactate uptake was pH‐ and concentration‐dependent, but sodium‐independent. Uptake was characterized by simple Michaelis‐Menton kinetics. Km, and Vmax estimates were 42.9 ± 9.4 mM, and 57.6 ± 10.3 nmol/mg/min for GHB. GHB was transported primarily in the apical to basolateral direction and was inhibited by the known MCT inhibitor α‐cyano‐4‐hydroxycinnamate, consistent with the apical localization of MCTs.ConclusionsMCTs contribute significantly to the transport of GHB in Caco‐2 cells. Further studies are needed to determine the contributions of MCT1, 2 and 4 to the intestinal transport of GHB.SupportNIH grant DA023223 and a fellowship for MAF from Pfizer Inc.