Epidermal growth factor and insulin short-term increase hPepT1-mediated glycylsarcosine uptake in Caco-2 cells

Aim: Little is known about the physiological regulation of the human intestinal di/tri-peptide transporter, hPepT1. In the present study we evaluated the effects of epidermal growth factor (EGF) and insulin on hPepT1-mediated dipeptide uptake in the intestinal cell line Caco-2. Methods: Caco-2 cells were grown on filters for 23-27 days. Apical dipeptide uptake was measured using [C-14]glycylsarcosine([C-14]Gly-Sar). HPepT1 mRNA levels were investigated using RT-PCR, cytosolic pH was determined using the pH-sensitive fluorescent probe BCECF. Results: Basolateral application of EGF increased [C-14]Gly-Sar uptake with an ED50 value of 0.77+/-0.25 ng mL(-1) (n=3-6) and a maximal stimulation of 33+/-2% (n=3-6). Insulin stimulated [(14) C]Gly-Sar uptake with an ED50 value of 3.5+/-2.0 ng mL(-1) (n=3-6) and a maximal stimulation of approximately 18% (n=3-6). Gly-Sar uptake followed simple Michaelis-Menten kinetics. K-m in control cells was 0.98+/-0.11 mM (n=8) and V-max was 1.86+/-0.07 nmol cm(-2) min(-1) (n=8). In monolayers treated with 200 ng mL(-1) of EGF, K-m was 1.11+/-0.05 mM (n=5) and V-max was 2.79+/-0.05 nmol cm(-2) min(-1) (n=5). In monolayers treated with 50 ng mL(-1) insulin, K-m was 1.03+/-0.08 mM and V-max was 2.19+/-0.06 nmol cm(-2) min(-1) (n=5). Kinetic data thus indicates an increase in the number of active transporters, following stimulation. The incrased Gly-Sar uptake was not accompanied by changes in hPepT1 mRNA, nor by measurable changes in cytosolic pH. Conclusions: Short-term stimulation with EGF and insulin caused an increase in hPepT1-mediated uptake of Gly-Sar in Caco-2 cell monolayers, which could not be accounted for by changes in hPepT1 mRNA or proton-motive driving force.