Characterization of L-lysine transport across equine and porcine jejunal and colonic brush border membrane

Abstract

In nonruminant herbivores, microbially derived AA could contribute to whole-body AA homeostasis and thus decrease predicted AA requirements. However, postileal capacity of AA uptake is currently unknown. Therefore, to test the hypothesis that Lys is transported across the large colon mucosal apical membrane with capacity similar to that of the small intestinal mucosa in the pony and pig, we examined Lys transport in vitro using brush border membrane vesicles (BBMV). Mucosa was collected from the distal jejunum (DJ) and proximal large colon (PLC) of growing pigs (n = 3) and ponies (n = 4), flash frozen in liquid nitrogen, and stored at -80°C. Jejunal and colonic BBMV were manufactured by Mg(2+) precipitation and used to determine initial rates and kinetics [the maximal transport rate (V(max)) and the Michaelis constant (K(M))] of l-Lys transport into apical epithelia by rapid filtration technique in Na(+)-gradient incubation buffer. Initial rates of total l-Lys uptake did not differ between the PLC and DJ in either the pig or the pony, or between the pony and the pig, at each l-Lys concentration. In the pig, compared with the DJ, l-Lys transport V(max) in the PLC did not differ (121 ± 26 and 180 ± 26 pmol•mg of protein(-1)•s(-1), respectively; P = 0.14) and l-Lys K(M) in the PLC tended to be greater (0.23 ± 0.22 and 0.89 ± 0.22 mM, respectively; P = 0.09). In the pony, compared with the DJ, l-Lys transport V(max) in the PLC was greater (62 ± 25 and 149 ± 25 pmol•mg of protein(-1)•s(-1), respectively; P = 0.04) and l-Lys K(M) in the PLC was greater (0.08 ± 0.22 and 1.05 ± 0.22 mM, respectively; P = 0.02). l-Lysine diffusion was not different between segments; however, total intestinal diffusion was greater (P = 0.03) in the pony than in the pig (115 ± 10 and 73 ± 10 pmol·mg of protein(-1)•s(-1), respectively). These results demonstrate that the large colon is capable of l-Lys transport across the apical epithelial membrane with greater capacity and less affinity than the jejunum, indicating that the large colon may play a significant role in l-Lys absorption and homeostasis in hindgut fermenters.

Orally supplemented l-arginine impairs amino acid absorption depending on dose in horses1

“…The explanation for the difference from these results and our study in horses is unclear. Woodward et al (2012) reported no differences in L-lysine transporter's Vmax or KM between porcine and equine jejunum and proximal colon, but that ponies had a greater diffusion of protein in brush border membrane vesicles from both sections than pigs. The question remains as to whether these transporters have varying affinity for l-Arg between species.…”

— Invited Review — Amino acid requirements in horses

“…Without confirmation of an in vivo study, some in vitro studies showed that Lalanine and cycloleu cine were actively transported through the serosa layer, but active transport of those amino acids through the mucosa layer was not observed in the equine cecum [39,40], pro viding evidence that there may not be substantial uptake of amino acids from the lumen of the large intestine. On the other hand, lysine transporters across the apical membrane in the equine and swine large colon were found to have a greater capacity but less affinity than those in the jejunum, suggesting meaningful hindgut absorption of lysine [41]. However, it is still unclear whether the proteolytic enzymes exist in the hindgut to degrade microbial protein and make it available for absorption.…”