Elimrani Ihsan, Lahjouji Karim, Seidman Ernest, Roy Marie-Josee, Mitchell Grant A, Qureshi Ijaz
Divisions of Medical Genetics and Gastroenterology, Research Center, Hôpital Sainte-Justine, Department of Pediatrics, Université de Montréal, Montreal, Quebec, Canada H3T 1C5.
Am J Physiol Gastrointest Liver Physiol. 2003 May;284(5):G863-71. doi: 10.1152/ajpgi.00220.2002. Epub 2003 Jan 10.
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-[(3)H]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 micro M 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.
左旋肉碱既来源于饮食摄入，也可通过生物合成产生。饮食中的肉碱在小肠中被吸收，然后分布到其他器官。先前使用Caco-2细胞进行的研究表明，肠道中左旋肉碱的转运涉及载体介导系统。本研究的目的是确定Caco-2细胞中左旋肉碱的摄取是否由最近鉴定出的有机阳离子/肉碱转运体（OCTN2）介导。在有或没有特异性抑制剂的情况下，研究了左旋[³H]肉碱摄取的动力学。成熟细胞中左旋肉碱的摄取依赖于钠，且随时间呈线性关系。饱和摄取的K(m)和V(max)值分别为14.07±1.70微摩尔和26.3±0.80皮摩尔·毫克蛋白⁻¹·6分钟⁻¹。丙戊酸盐和其他有机阳离子可抑制（P<0.05 - 0.01）左旋肉碱的摄取。抗OCTN2抗体识别出Caco-2细胞刷状缘膜（BBM）中一种表观分子量为60 kDa的蛋白质。通过双重免疫染色证实了OCTN2的表达。我们的结果表明，分化的Caco-2细胞中左旋肉碱的摄取主要由位于BBM上的OCTN2介导。
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