Expression and distribution of monocarboxylate transporter 1 (MCT1) in the gastrointestinal tract of calves D. Kirat a , H. Inoue a , H. Iwano b , K. Hirayama c , H. Yokota b , H. Taniyama c , S. Kato a, * a Department of Veterinary Physiology, School of Veterinary Medicine, Rakuno Gakuen University, 582-1 Bunkyodai-Midorimachi, Ebetsu, Hokkaido 069-8501, Japan b Department of Veterinary Biochemistry, School of Veterinary Medicine, Rakuno Gakuen University, 582-1 Bunkyodai-Midorimachi, Ebetsu, Hokkaido 069-8501, Japan c Department of Veterinary Pathology, School of Veterinary Medicine, Rakuno Gakuen University, 582-1 Bunkyodai-Midorimachi, Ebetsu, Hokkaido 069-8501, Japan Accepted 4 November 2004 Abstract In the present study the expression and distribution of monocarboxylate transporter 1 (MCT1) along the gastrointestinal tract (rumen, reticulum, omasum, abomasum, duodenum, jejunum, ileum, cecum and colon) of calves were investigated on both mRNA and protein levels. The expression of MCT1 protein and its distribution were determined by Western blotting and immunohistochemical staining, respectively by using antibody for MCT1. MCT1 protein was visualized as a 43-kDa band on immunoblots of the membrane proteins prepared from the various regions examined, and it was more highly expressed in forestomach and large intestine than in abomasum and small intestine. With the use of reverse transcriptase–polymerase chain reaction, mRNA encoding for MCT1 was demonstrated in the different tissues examined. The immunohistochemical study confirmed the Western blot findings and showed strong MCT1 immunopositive staining in the stratified squamous epithelia of the forestomach as well as the epithelial cells lining the digestive tract in the cecum, proximal colon, and distal colon. The results suggest that MCT1 may play a role in the transport of SCFA and their metabolites in the gastrointestinal tract of bovines. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Monocarboxylate transporter 1; Gastrointestinal tract; Calves; RT–PCR; Western blot; Immunohistochemistry 1. Introduction Short chain fatty acids (SCFA) are produced in large amounts in the gastrointestinal tract of herbivo- rous animal species, especially in the forestomach of ruminants, as a result of the microbial fermentation of carbohydrates. The production and absorption of SCFA have a very significant effect on the epithelial cell growth, blood flow, and the normal secretory and absorptive functions of the rumen and large intes- tine (Bergman, 1990). The principal SCFA in either the rumen or large intestine are acetate, propionate, and butyrate and they contribute about 70% of the caloric requirements of ruminants (Bergman, 1990). A high portion of SCFA is metabolized intracellularly (Berg- man, 1990; Britton and Krehbiel, 1993). The end prod- ucts of SCFA metabolism are ketone bodies and lactic acid. Transport of SCFA and other monocarboxylates; lactate, pyruvate and ketone bodies are of a major physiological importance to almost all cells. A number 0034-5288/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.rvsc.2004.11.007 * Corresponding author. Tel: +81 11 388 4734; fax: +81 11 387 5890. E-mail address: kato@rakuno.ac.jp (S. Kato). www.elsevier.com/locate/rvsc Research in Veterinary Science 79 (2005) 45–50