σ receptor ligand-induced up-regulation of the H+/peptide transporter PEPT1 in the human intestinal cell line Caco-2

We determined the effects of (+)pentazocine, a selective a, ligand, on the uptake of glycylsarcosine (Gly-Sar) in the human intestinal cell line Caco-2 which expresses the low affinity/high capacity peptide transporter PEPT1. Confluent Caco-2 cells were treated with various concentrations of (+)pentazocine for desired time (mostly 24 hr). The activity of PEPT1 was assessed by measuring the uptake of [C-14]Gly-Sar in the presence of a H+ gradient. (+)Pentazocine increased the uptake of [C-14]Gly-Sar mediated by PEPT1 in a concentration- and time-dependent manner. Kinetic analyses have indicated that (+)pentazocine increased the maximal velocity (V-max) for Gly-Sar uptake in Caco-2 cells without affecting the Michaelis Menten constant (K-t). In addition, semi-quantitative RT-PCR revealed that treatment of (+)pentazocine increased PEPT1 mRNA in Caco-2 cells in a concentration-dependent manner. These data suggest that a, receptor ligand (+)pentazocine up-regulates PEPT1 in Caco-2 cells at the level of increased mRNA, causing an increase in the density of the transporter protein in the cell membrane. (C) 1999 Academic Press.