Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, State University of New York, Amherst, New York, USA.
Drug Metab Dispos. 2010 Mar;38(3):441-7. doi: 10.1124/dmd.109.030775. Epub 2009 Dec 1.
The objectives of this study were to determine mRNA expression of monocarboxylate transporters (MCT) and to evaluate intestinal transport of the MCT substrates gamma-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: K(m) = 17.6 +/- 10.5 mM, V(max) = 17.3 +/- 11.7 nmol/min/mg, and P = 0.38 +/- 0.15 microl/min/mg; and d-lactate: K(m) = 6.0 +/- 2.9 mM, V(max) = 35.0 +/- 18.4 nmol/min/mg, and P = 1.3 +/- 0.6 microl/min/mg). The uptake of GHB and d-lactate was significantly decreased by the known MCT inhibitor alpha-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.
本研究旨在确定单羧酸转运体（MCT）的 mRNA 表达，并评估 MCT 底物 γ-羟基丁酸（GHB）和 d-乳酸在人肠道 Caco-2 细胞中的肠内转运。在 Caco-2 细胞中观察到 MCT1、2、3 和 4 的 mRNA 存在。证明 GHB 和 d-乳酸在 Caco-2 细胞中的摄取均依赖于 pH 值和浓度，且与钠离子无关。GHB 和 d-乳酸的摄取最好用米氏方程和被动扩散来描述（GHB：K(m) = 17.6 +/- 10.5 mM，V(max) = 17.3 +/- 11.7 nmol/min/mg，P = 0.38 +/- 0.15 microl/min/mg；d-乳酸：K(m) = 6.0 +/- 2.9 mM，V(max) = 35.0 +/- 18.4 nmol/min/mg，P = 1.3 +/- 0.6 microl/min/mg）。已知的 MCT 抑制剂α-氰基-4-羟基肉桂酸和 MCT 底物 GHB 和 d-乳酸显著降低了 GHB 和 d-乳酸的摄取，但有机阳离子四乙铵氯化物则没有。GHB 和 d-乳酸的定向通量研究表明，涉及载体介导的运输，顶端至基底外侧的渗透性高于基底外侧至顶端的渗透性。这些发现证实了 MCT1-4 在 Caco-2 细胞中的存在，并证明了 GHB 和 d-乳酸的转运特征与质子依赖的 MCT 介导的转运一致。
