Volatile fatty acids production in ruminants and the role of monocarboxylate transporters: A review
Monocarboxylates commonly referred to as short-chain fatty acids (SCFAs) are metabolized to different extents by the epithelium of the gastrointestinal tract. They are absorbed along different segments of the gastrointestinal tract and constitute a significant amount of energy in ruminants. Monocarboxylates play a central role in cellular metabolism and metabolic communication between tissues. Essential to these roles is their rapid transport across the plasma membrane, which is catalyzed by a recently identified family of proton-linked monocarboxylate transporters (MCTs). Monocarboxylate transporter-1 and 4 have been shown to interact specifically with OX-47 (CD147), a member of the immunoglobulin superfamily with a single transmembrane helix. This interaction appears to assist MCT expression at the cell surface. Despite the importance of short-chain fatty acids in being the main energy source in ruminant animals, the mechanism of SCFAs transport and absorption is still not fully studied. The aim of this review is to critically discuss short-chain fatty acids production and the functional role of monocarboxylate transporters in relation to the transport and absorption of these nutrients along the gastrointestinal tract of ruminants. Two major functions of monocarboxylate transporter proteins, namely the facilitation of the absorption of SCFAs in the gastrointestinal tract and the regulation of cell pH in skeletal muscles, are clearly very important for physiological homeostasis, animal welfare and productivity.
Key words: Ruminants, monocarboxylates, monocarboxylate transporters, CD147.