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J Physiol Volume 576, Number 2, 635-647, October 15, 2006 DOI: 10.1113/jphysiol.2006.115931
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ALIMENTARY

Monocarboxylate transporter 1 (MCT1) plays a direct role in short-chain fatty acids absorption in caprine rumen

Doaa Kirat1, Junji Masuoka1, Hideaki Hayashi1, Hidetomo Iwano2, Hiroshi Yokota2, Hiroyuki Taniyama3 and Seiyu Kato1

Department of
1 Veterinary Physiology
2 Veterinary Biochemistry
3 Veterinary Pathology, School of Veterinary Medicine, Rakuno Gakuen University, 582 Bunkyodai-Midorimachi, Ebetsu, Hokkaido 069-8501, Japan

Despite the importance of short-chain fatty acids (SCFA) in maintaining the ruminant physiology, the mechanism of SCFA absorption is still not fully studied. The goal of this study was to elucidate the possible involvement of monocarboxylate transporter 1 (MCT1) in the mechanism of SCFA transport in the caprine rumen, and to delineate the precise cellular localization and the level of MCT1 protein along the entire caprine gastrointestinal tract. RT-PCR revealed the presence of mRNA encoding for MCT1 in all regions of the caprine gastrointestinal tract. Quantitative Western blot analysis showed that the level of MCT1 protein was in the order of rumen ≥ reticulum > omasum > caecum > proximal colon > distal colon > abomasum > small intestine. Immunohistochemistry and immunofluorescence confocal analyses revealed widespread immunoreactive positivities for MCT1 in the caprine stomach and large intestine. Amongst the stratified squamous epithelial cells of the forestomach, MCT1 was predominantly expressed on the cell boundaries of the stratum basale and stratum spinosum. Double-immunofluorescence confocal laser-scanning microscopy confirmed the co-localization of MCT1 with its ancillary protein, CD147 in the caprine gastrointestinal tract. In vivo and in vitro functional studies, under the influence of the MCT1 inhibitors, p-chloromercuribenzoate (pCMB) and p-chloromercuribenzoic acid (pCMBA), demonstrated significant inhibitory effect on acetate and propionate transport in the rumen. This study provides evidence, for the first time in ruminants, that MCT1 has a direct role in the transepithelial transport and efflux of the SCFA across the stratum spinosum and stratum basale of the forestomach toward the blood side.

(Received 26 June 2006; accepted after revision 3 August 2006; first published online 10 August 2006)
Corresponding author S. Kato: Department of Veterinary Physiology, School of Veterinary Medicine, Rakuno Gakuen, University, 582 Bunkyodai-Midorimachi, Ebetsu, Hokkaido 069-8501, Japan. Email: kato{at}rakuno.ac.jp






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