Peptide Transporter 1 Is Responsible for Intestinal Uptake of the Dipeptide Glycylsarcosine: Studies in Everted Jejunal Rings from Wild-type and Pept1 Null Mice

The purpose of this study was to determine the relative importance of peptide transporter 1 (PEPT1) in the uptake of peptides/mimetics from mouse small intestine, using glycylsarcosine (GlySar). After isolating jejunal tissue from wild-type and Pept1 null mice, 2 cm intestinal segments were everted and mounted on glass rods for tissue uptake studies. [14C]GlySar (4 μM) was studied as a function of time, temperature, sodium and pH, concentration, and potential inhibitors. Compared with wild-type animals, Pept1 null mice exhibited a 78% reduction in GlySar uptake at pH 6.0 at 37°C. GlySar uptake showed pH dependence, with peak values between pH 6.0 and 6.5 in wild-type animals, whereas no such tendency was observed in Pept1 null mice. GlySar exhibited Michaelis-Menten uptake kinetics and a minor nonsaturable component in wild-type animals. In contrast, GlySar uptake occurred only by a nonsaturable process in Pept1 null mice. GlySar uptake was significantly inhibited by dipeptides, aminocephalosporins, angiotensin-converting enzyme inhibitors, and the antiviral prodrug valacyclovir; these inhibitors had little, if any, effect on the uptake of GlySar in Pept1 null mice. The findings demonstrate that PEPT1 plays a critical role in the uptake of GlySar in jejunum and suggest that PEPT1 is the major transporter responsible for the intestinal absorption of small peptides.