Dipeptide transport in Yucatan miniature piglet intestine

The PepT1 transporter is getting much attention in modem nutrition due to its universal substrate affinity for di/tripeptides which facilitates efficient transport of amino acids. As such, di/tripeptides may be an important component of amino acid nutrition because they are transported into enterocytes more efficiently than a mixture of free amino acids. However, limited data are available on the contribution of PepT1 to total peptide uptake. We studied the contribution of PepT1-mediated transport versus paracellular movement to total dipeptide uptake in intestinal samples excised from suckling piglets. Using an in vitro Ussing chamber model, we determined that PepT1 was responsible for 46% of the glycyl-sarcosine uptake by piglet jejunum and 73% of the glycyl-sarcosine uptake by piglet ileum; these values are lower than previously reported in cell culture models, suggesting that paracellular peptide uptake is quantitatively important in young piglets. -- PepT1 and amino acid transport systems both contribute to amino acid uptake by enterocytes, but the contribution of the different routes to overall amino acid absorption has not yet been defined. Furthermore, very little is known about the interaction between free amino acid and peptide uptake at the cellular level. Using an in vivo gut loop perfusion model in piglets, we demonstrated that arginine uptake was enhanced by 81% when perfused simultaneously with 20 mM lysyl-lysine, compared to control. In contrast, perfusing loops with equimolar lysyl-glycine did not alter arginine uptake. We speculated that enhanced uptake of arginine was likely due to trans-stimulation of rBAT/b⁰⁺ transporter. Dipeptides are taken up by enterocytes via PepT1 and are then hydrolyzed to release free lysine. High intracellular free lysine trans-stimulates the rBAT/b⁰⁺ anti-transporter to enhance arginine uptake. When lysyl-lysine was perfused with an amino peptidase inhibitor (amastatin), the potentiating effect was abolished, suggesting that this trans-stimulation activity was impeded by reducing intracellular hydrolysis of dipeptides. To the best of my knowledge we are the first to demonstrate the interaction between arginine absorption and lysine-containing dipeptides at the cellular level in an in situ model