Characterization of butyrate transport across the luminal membranes of equine large intestine

Nedjadi, Taoufik, Moran, Andrew ORCID: 0000-0003-0031-2154, Al-Rammahi, Miran A ORCID: 0000-0002-0165-7990 and Shirazi-Beechey, Soraya
(2014) Characterization of butyrate transport across the luminal membranes of equine large intestine. Experimental Physiology, 99 (10). 1335 - 1347.

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New Findings: What is the central question of this study? Butyrate, a product of colonic microbial fermentation of dietary fibre (grass), is a major source of energy for the horse and plays an important role in maintaining the health of the intestine. What are the properties of the membrane protein and what is the mechanism by which butyrate is absorbed in equine large intestine (colon)? What is the main finding and its importance? We have identified the mechanism of and membrane protein involved in butyrate transport in equine large intestine. This knowledge will allow rational approaches to the design of dietary formulations to enhance butyrate production and absorption in equine colon, in order to provide more energy for the horse and maintain its gut health. The diet of the horse, pasture forage (grass), is fermented by the equine colonic microbiota to short‐chain fatty acids, notably acetate, propionate and butyrate. Short‐chain fatty acids provide a major source of energy for the horse and contribute to many vital physiological processes. We aimed to determine both the mechanism of butyrate uptake across the luminal membrane of equine colon and the nature of the protein involved. To this end, we isolated equine colonic luminal membrane vesicles. The abundance and activity of cysteine‐sensitive alkaline phosphatase and villin, intestinal luminal membrane markers, were significantly enriched in membrane vesicles compared with the original homogenates. In contrast, the abundance of GLUT2 protein and the activity of Na+–K+‐ATPase, known markers of the intestinal basolateral membrane, were hardly detectable. We demonstrated, by immunohistochemistry, that monocarboxylate transporter 1 (MCT1) protein is expressed on the luminal membrane of equine colonocytes. We showed that butyrate transport into luminal membrane vesicles is energized by a pH gradient (out < in) and is not Na+ dependent. Moreover, butyrate uptake is time and concentration dependent, with a Michaelis–Menten constant of 5.6 ± 0.45 mm and maximal velocity of 614 ± 55 pmol s−1 (mg protein)−1. Butyrate transport is significantly inhibited by p‐chloromercuribenzoate, phloretin and α‐cyano‐4‐hydroxycinnamic acid, all potent inhibitors of MCT1. Moreover, acetate and propionate, as well as the monocarboxylates pyruvate and lactate, also inhibit butyrate uptake. Data presented here support the conclusion that transport of butyrate across the equine colonic luminal membrane is predominantly accomplished by MCT1.

Item Type: Article
Depositing User: Symplectic Admin
Date Deposited: 21 Jul 2015 13:22
Last Modified: 28 Nov 2021 01:11
DOI: 10.1113/expphysiol.2014.077982
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