Abstract
We determined the effects of (+)pentazocine, a selective ς1 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 [14C]Gly-Sar in the presence of a H+ gradient. (+)Pentazocine increased the uptake of [14C]Gly-Sar mediated by PEPT1 in a concentration- and time-dependent manner. Kinetic analyses have indicated that (+)pentazocine increased the maximal velocity (Vmax) for Gly-Sar uptake in Caco-2 cells without affecting the Michaelis-Menten constant (Kt). 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 ς1 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.
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