Gill Ravinder K, Saksena Seema, Alrefai Waddah A, Sarwar Zaheer, Goldstein Jay L, Carroll Robert E, Ramaswamy Krishnamurthy, Dudeja Pradeep K
Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois at Chicago, Medical Research Service (600/151), Jesse Brown Veterans Affairs Medical Center, 820 South Damen Ave., Chicago, Illinois 60612, USA.
Am J Physiol Cell Physiol. 2005 Oct;289(4):C846-52. doi: 10.1152/ajpcell.00112.2005. Epub 2005 May 18.
Recent studies from our laboratory and others have demonstrated the involvement of monocarboxylate transporter (MCT)1 in the luminal uptake of short-chain fatty acids (SCFAs) in the human intestine. Functional studies from our laboratory previously demonstrated kinetically distinct SCFA transporters on the apical and basolateral membranes of human colonocytes. Although apical SCFA uptake is mediated by the MCT1 isoform, the molecular identity of the basolateral membrane SCFA transporter(s) and whether this transporter is encoded by another MCT isoform is not known. The present studies were designed to assess the expression and membrane localization of different MCT isoforms in human small intestine and colon. Immunoblotting was performed with the purified apical and basolateral membranes from human intestinal mucosa obtained from organ donor intestine. Immunohistochemistry studies were done on paraffin-embedded sections of human colonic biopsy samples. Immunoblotting studies detected a protein band of approximately 39 kDa for MCT1, predominantly in the apical membranes. The relative abundance of MCT1 mRNA and protein increased along the length of the human intestine. MCT4 (54 kDa) and MCT5 (54 kDa) isoforms showed basolateral localization and were highly expressed in the distal colon. Immunohistochemical studies confirmed that human MCT1 antibody labeling was confined to the apical membranes, whereas MCT5 antibody staining was restricted to the basolateral membranes of the colonocytes. We speculate that distinct MCT isoforms may be involved in SCFA transport across the apical or basolateral membranes in polarized colonic epithelial cells.
我们实验室及其他机构最近的研究表明，单羧酸转运体（MCT）1参与了人体肠道中短链脂肪酸（SCFA）的腔内摄取。我们实验室先前的功能研究表明，人结肠细胞顶膜和基底外侧膜上存在动力学特性不同的SCFA转运体。尽管顶膜SCFA摄取由MCT1亚型介导，但基底外侧膜SCFA转运体的分子身份以及该转运体是否由另一种MCT亚型编码尚不清楚。本研究旨在评估不同MCT亚型在人小肠和结肠中的表达及膜定位。使用从器官捐献者肠道获取的人肠黏膜纯化顶膜和基底外侧膜进行免疫印迹分析。对人结肠活检样本的石蜡包埋切片进行免疫组织化学研究。免疫印迹研究检测到MCT1约39 kDa的蛋白条带，主要存在于顶膜中。MCT1 mRNA和蛋白的相对丰度沿人肠道长度增加。MCT4（54 kDa）和MCT5（54 kDa）亚型显示基底外侧定位，且在远端结肠中高表达。免疫组织化学研究证实，人MCT1抗体标记局限于顶膜，而MCT5抗体染色局限于结肠细胞的基底外侧膜。我们推测，不同的MCT亚型可能参与极化结肠上皮细胞中SCFA跨顶膜或基底外侧膜的转运。
