Methionine (Met) is an essential amino acid (EAA) playing an important role in protein synthesis and regulating various cellular & physiological pathways . In mammals, Met absorption can be achieved by sodium dependent and/or sodium independent solute carrier transporters located in apical (mucosal) and basolat eral (serosal) membranes of intestinal epithelial cells. However, the knowledge of how Met absorbed in fish intestine, a critical site for animal nutrient uptakes, has not been fully understood .
This study was aimed to describe the fundamental properties of Met transport along trout gut . Specifically, Met transport in the presence or absence of sodium was assessed in three intestinal segments including pyloric caeca (PC), midgut (MG) and hindgut (HG) using 14C radiolabe led DL-Met flux ; and identification of Met-link transporters involved using gene expression.
The results demonstrated that Met transport was strictly dependent on sodium and obeyed saturable manners. This indicated the existence of Na+-dependent transporters as the driving force in fish gut. This was supported with the gene expression of sodium-methionine cotransporters such as ASCT2 (SLC1A5), B0AT1-like (SLC6A19-like) and y+ LAT1 (SLC7A7). On the contrary, the flux rate of DL-[14C] Met was not a function of substrate concentration when the assays were performed in Na+-free buffer. This was in line with the absence of Na+-independent transporter b0,+AT (SLC7A9) in trout genome and no/low expression of LAT1 (SLC7A5), LAT2 (SLC7A8), LAT3 (SLC43A1) . U nderstandings the function and expression of these transporters are informative for practical endeavor through feed formulation since DL-Met is commonly supplemented in commercial fish feed. Future direction moves towards investigating the potential interaction of Met with some other AA s. This contributes to explain AAs transport antagonism and dietary AAs balance.