INTERACTION OF BETA-LACTAM ANTIBIOTICS WITH H+ PEPTIDE COTRANSPORTERSIN RAT RENAL BRUSH-BORDER MEMBRANES/

Two H+/peptide cotransporters, PEPT1 and PEPT2, are expressed in the k idney, mediating the renal tubular reabsorption of oligopeptides and b eta-lactam antibiotics. We examined the interactions of beta-lactam an tibiotics with peptide transporters in rat renal brush-border membrane s by evaluating the inhibitory potencies of the antibiotics against gl ycylsarcosine transport. Western blot analysis revealed that PEPT1 and PEPT2 were expressed in the renal brush-border membranes with the app arent molecular masses of 75 and 105 kDa, respectively. Using renal br ush-border membrane vesicles, the uphill transport of glycylsarcosine was observed in the presence of an inward H+ gradient and an inside-ne gative membrane potential. Two transport systems with high affinity (K -m of 50 mu M) and low affinity (K-m of 1.2 mM) appeared kinetically t o mediate the glycylsarcosine uptake. The inhibition constants of the antibiotics for glycylsarcosine transport were more closely correlated with those in stable LLC-PK1 cells transfected with rat PEPT2 rather than PEPT1 cDNA. The beta-lactam antibiotics with an oc-amino group sh owed trans-stimulation effects on the glycylsarcosine uptake, suggesti ng that these antibiotics and glycylsarcosine share a common peptide t ransporter. However, the antibiotics lacking an alpha-amino group fail ed to show the trans-stimulation effect. It is concluded that amino-be ta-lactam antibiotics at therapeutic concentrations interact predomina ntly with PEPT2 localized in the brush-border membranes of rat kidney.