AJP - Cell Physiology, Vol 257, Issue 5 C971-C975, Copyright © 1989 by American Physiological Society
Low-affinity transport of pyroglutamyl-histidine in renal brush-border membrane vesicles
H. A. Skopicki, K. Fisher, D. Zikos, G. Flouret and D. R. Peterson
Department of Physiology, University of Health Sciences, Chicago Medical School, Illinois.
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 (Kt) = 9.3 X 10(-8) M, Vmax = 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 Kt of 6.3 X
10(-5) M and a Vmax 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.
