Received March 2, 2006
Revised April 21, 2006
Accepted after revision July 10, 2006

¹ Department of Physiology, School of Veterinary Medicine, Rakuno Gakuen University, Hokkaido, Japan

^* To whom correspondence should be addressed. E-mail: kato{at}rakuno.ac.jp.

	Abstract

The current study was undertaken to investigate the functional role of monocarboxylate transporter 1 (MCT1) in the ruminant large intestine. mRNA encoding for MCT1 was verified by RT-PCR in cecum, proximal colon and distal colon of adult cattle. Both of the Immunohistochemistry and the confocal laser microscopy verified that the MCT1 protein was abundant at the surface epithelium of the large intestine and the amount decreased from the tip 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 cecum 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 cecum via Ussing chamber technique. The acetate absorption was found to be pH-dependent, and the rate of acetate absorption was increased as the pH decreased. The serosal application of the MCT1 inhibitor, p-chloromercuribenzoic acid (pCMB) significantly reduced the transport of acetate across the cecal epithelium of cows. In addition, the transport of acetate was significantly reduced in the presence of its analog, propionate, indicating that acetate and propionate compete for binding to the same transporter. The obtained results concluded that MCT1 is a major route for SCFA efflux across the basolateral membrane of bovine large intestine and it could play a role in the intracellular pH regulation.

Key Words: Absorption, Gene expression, Intestine