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1 Division of Medical Genetics, Hopital Sainte-Justine, Universite de Montreal, Montreal, Quebec, Canada
2 Division of Gastroenterology/ Research Center, Department of Pediatrics, Hopital Sainte-Justine, Universite de Montreal, Montreal, Quebec, Canada
* To whom correspondence should be addressed. E-mail: aqureshi{at}justine.umontreal.ca.
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). The kinetics of L-[3H]carnitine uptake was investigated with or without specific inhibitors. L-Carnitine uptake in mature cells was sodium-dependent and linear with time. Km and Vmax values for saturable uptake were 14.07 ± 1.70 mmol/L and 26.3 ± 0.80 pmol/mg protein/6 min, 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.
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