Low-affinity transport of pyroglutamyl-histidine in renal brush-border membrane vesicles

These studies were performed to determine if a low-affinity carrier is present in the luminal membrane of proximal tubular cells for the transport of the dipeptide, pyroglutamyl-histidine (pGlu-His). We have previously described the existence of a specific, high-affinity, low-capacity [transport constant (K(t)) = 9.3 x 10^-8 M, V(max) = 6.1 x 10^-12 mol·mg^-1·min^-1] carrier for pGlu-His in renal brush-border membrane vesicles. In the present study, we sought to demonstrate that multiple carriers exist for the transport of a single dipeptide by determining whether a low-affinity carrier also exists for the uptake of pGlu-His. Transport of pGlu-His into brush-border membrane vesicles was saturable over the concentration range of 10^-5-10^-3 M, yielding a K(t) of 6.3 x 10^-5 M and a V(max) of 2.2 x 10^-10 mol·mg^-1·min^-1. Uptake was inhibited by the dipeptides glycyl-proline, glycyl-sarcosine, and carnosine but not by the tripeptide pyroglutamyl-histidyl-prolinamide. We conclude that 1) pGlu-His is transported across the luminal membrane of the proximal tubule by multiple carriers and 2) the lower affinity carrier, unlike the higher affinity carrier, is nonspecific with respect to other dipeptides.