Role of proton-coupled oligopeptide transporter 1 in small peptide absorption in the bovine forestomach

Abstract Text:

In this work, transepithelial transport of glycylsarcosine (Gly-Sar) in bovine forestomach cells was determined to investigate the role of proton-coupled oligopeptide transporter 1 (PEPT1) in small peptide absorption. Primary cultured omasal epithelial cell (OEC) and rumen epithelial cell (REC) monolayers derived from newborn Chinese Holstein male calves were grown in transwell set-up. The transepithelial electrical resistance of transwell model reached plateau after a week, and that of OEC monolayers was higher than that of REC monolayers (2468 ± 216 vs. 1918 ± 33 Ω•cm²). Fluorescein sodium was used to measure the permeability of monolayers. After 150 min, transmittances of fluorescein sodium across OEC and REC monolayers were 0.63 and 0.19%, respectively whereas that of control (blank filter) was 12.0%. The monolayers were then used for incubation with various concentrations of Gly-Sar in apical side at various pH values or at 37°C and 4°C for various times. In addition, mRNA of PEPT1 was detected in OECs and RECs. The cells were also incubated in absence or presence of 0.5 mM diethylpyrocarbonate, an inhibitor of PEPT1. Transportation of Gly-Sar was dependent on concentration, incubation time, temperature and pH value. Accumulation of Gly-Sar in basolateral side (pH 7.4) increased with the increasing level of Gly-Sar and reached a plateau at 5 mM. Transportation of Gly-Sar by OEC monolayers was higher at 37°C compared to 4°C (P < 0.05), with an optimal pH of 6.0-6.5, and inhibited by diethylpyrocarbonate. In addition, accumulation of Gly-Sar in basolateral side of OEC monolayers was greater than that of REC (P< 0.05), indicating that the OECs have greater ability to transport Gly-Sar than RECs. In summary, the PEPT1 plays an important role in small peptide absorption in bovine forestomachs.

Keywords: bovine forestomach epithelial cells; oligopeptide transporter 1; transport