Carrier-mediated transport of pyroglutamyl-histidine in renal brush border membrane vesicles

These studies were performed to determine if a transmembrane carrier for pyroglutamyl-histidine (pGlu-His) is present in the luminal membrane or renal proximal tubular cells. Previous studies have suggested the intact transepithelial transport of pGlu-His, a dipeptide formed by the hydrolysis of luteinizing hormone-releasing hormone by enzymes associated with the brush border in the proximal nephron. With the use of a renal brush border membrane vesicle preparation, pGlu-His showed H⁺-stimulated, Na-independent, saturable transport into an osmotically active space. High-pressure liquid chromatographic analysis of both the intravesicular and extravesicular fluids indicated intact uptake of the dipeptide. The transport constant (K(t)) and V(max) for pGlu-His transport were 9.3 x 10^-8 M and 6.1 x 10^-12 mol·mg^-1·min^-1, respectively. Transport of pGlu-His was not inhibited by the dipeptides glycyl-proline, glycyl-sarcosine, and N-β-alanyl-L-histidine, which have been previously shown to be transported into renal brush border vesicles via a single, low-affinity, high-capacity, Na-independent, and H⁺-stimulated peptide carrier. In addition, the γ-glutamyl-containing peptides γ-glutamyl-histidine and N(N-L-γ-glutamyl-L-cysteinyl)glycine and the tripeptide pyroglutamyl-histidyl-prolinamide were without an inhibitory effect. In contrast, transport of pGlu-His was inhibited by the dipeptide pyroglutamyl-alanine. This study demonstrates the existence of a high-affinity, low-capacity H⁺ cotransport system for pGlu-His in the proximal tubular luminal plasmalemma, which appears to be specific for pyroglutamyl-containing dipeptides. The data indicate that multiple dipeptide carriers are present in the proximal nephron.