Kirat Doaa, Kato Seiyu
Department of Veterinary Physiology, School of Veterinary Medicine, Rakuno Gakuen University, Ebetsu, Hokkaido 069-8501, Japan.
Exp Physiol. 2006 Sep;91(5):835-44. doi: 10.1113/expphysiol.2006.033837. Epub 2006 Jul 20.
The present study was undertaken to investigate the functional role of monocarboxylate transporter 1 (MCT1) in the ruminant large intestine. Messenger RNA encoding for MCT1 was verified by reverse transcriptase-polymerase chain reaction in caecum, proximal colon and distal colon of adult cattle. Both immunohistochemistry and confocal laser microscopy verified that the MCT1 protein was abundant in the surface epithelium of the large intestine, and the amount decreased from the opening of the crypt to its base. In the immunopositive cells, MCT1 was primarily localized in the basolateral membranes of epithelium lining the large intestine. Western blotting indicated that the levels of MCT1 protein were highest in the caecum, followed by proximal colon and then distal colon. In vitro studies were conducted to elucidate the possible involvement of MCT1 in the transport of short-chain fatty acids (SCFA) across the isolated mucosal sheets of cattle caecum using the Ussing chamber technique. Acetate absorption was found to be pH dependent, and the rate of acetate absorption increased as pH decreased. The serosal application of the MCT1 inhibitor 'p-chloromercuribenzoic acid (pCMB)' significantly reduced the transport of acetate across the caecal epithelium of cows. In addition, the transport of acetate was significantly reduced in the presence of its analogue, propionate, indicating that acetate and propionate compete for binding to the same transporter. The results show that MCT1 is a major route for SCFA efflux across the basolateral membrane of bovine large intestine and that it could play a role in the regulation of intracellular pH.
本研究旨在探讨单羧酸转运蛋白1（MCT1）在反刍动物大肠中的功能作用。通过逆转录-聚合酶链反应在成年牛的盲肠、近端结肠和远端结肠中验证了编码MCT1的信使核糖核酸。免疫组织化学和共聚焦激光显微镜检查均证实，MCT1蛋白在大肠表面上皮中含量丰富，且从隐窝开口至底部含量逐渐减少。在免疫阳性细胞中，MCT1主要定位于大肠内衬上皮的基底外侧膜。蛋白质印迹法表明，MCT1蛋白水平在盲肠中最高，其次是近端结肠，然后是远端结肠。采用Ussing室技术进行体外研究，以阐明MCT1在短链脂肪酸（SCFA）跨牛盲肠分离黏膜片转运中的可能作用。发现乙酸盐吸收依赖于pH值，且随着pH值降低，乙酸盐吸收速率增加。MCT1抑制剂“对氯汞苯甲酸（pCMB）”的浆膜应用显著降低了乙酸盐跨奶牛盲肠上皮的转运。此外，在其类似物丙酸盐存在的情况下，乙酸盐的转运显著降低，表明乙酸盐和丙酸盐竞争结合同一转运体。结果表明，MCT1是SCFA跨牛大肠基底外侧膜流出的主要途径，并且它可能在细胞内pH值调节中发挥作用。
