Expression and localization of organic cation/carnitine transporter OCTN2 in Caco-2 cells

L-Carnitine is derived both from dietary sources and biosynthesis. Dietary carnitine is absorbed in the small intestine and then distributed to other organs. Previous studies using Caco-2 cells demonstrated that the transport of L-carnitine in the intestine involves a carrier-mediated system. The purpose of this study was to determine whether the uptake of L-carnitine in Caco-2 cells is mediated by the recently identified organic cation/carnitine transporter (OCTN2). Kinetics of L-[H-3] carnitine uptake were investigated with or without specific inhibitors. L- Carnitine uptake in mature cells was sodium dependent and linear with time. K-m and V-max values for saturable uptake were 14.07 +/- 1.70 muM and 26.3 +/- 0.80 pmol . mg protein(-1) . 6 min(-1), respectively. L-carnitine uptake was inhibited (P < 0.05-0.01) by valproate and other organic cations. Anti-OCTN2 antibodies recognized a protein in the brush-border membrane (BBM) of Caco-2 cells with an apparent molecular mass of 60 kDa. The OCTN2 expression was confirmed by double immunostaining. Our results demonstrate that L- carnitine uptake in differentiated Caco-2 cells is primarily mediated by OCTN2, located on the BBM.