Involvement of thiol groups in the function of the dipeptide/proton cotransport system in rabbit renal brush-border membrane vesicles

The mechanism responsible for enhanced reabsorption of phosphate (Pi) in growing animals was assessed in renal brush-border membrane vesicles (BBMV) prepared from 3- to 14-day-old and greater than 57-day-old guinea pigs. On standard diet, Vmax (pmol.mg-1.s-1) of Na+-Pi cotransport was higher (P less than 0.001) in newborn (650 +/- 77) than in adult (144 +/- 17) but Vmax of Na+-glucose cotransport did not differ with age. Low dietary Pi did not affect significantly Vmax of Na+-Pi cotransport in the newborn (P greater than 0.8) but increased it in the adult (to 318 +/- 32, P less than 0.05). A high Pi intake resulted in a smaller relative decrease in Vmax in the newborn than in the adult (27 vs. 44%, P less than 0.05). In the newborn, the serum Pi (mM) decreased on a low-Pi diet (from 1.8 +/- 0.1 to 0.8 +/- 0.1, P less than 0.001) and rose by twofold on the high-Pi diet (to 3.5 +/- 0.2, P less than 0.001). In the adult, there were no significant changes in serum Pi with changes in Pi intake (P greater than 0.5). Thus in the newborn the Na+-Pi cotransport system is characterized by high transport capacity but low adaptability to changes in dietary Pi.

Download Full-text

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

AJP Cell Physiology ◽

10.1152/ajpcell.1989.257.5.c971 ◽

1989 ◽

Vol 257 (5) ◽

pp. C971-C975 ◽

Cited By ~ 3

Author(s):

H. A. Skopicki ◽

K. Fisher ◽

D. Zikos ◽

G. Flouret ◽

D. R. Peterson

Keyword(s):

Brush Border ◽

Brush Border Membrane ◽

Membrane Vesicles ◽

Brush Border Membrane Vesicles ◽

Proximal Tubular Cells ◽

Tubular Cells ◽

Luminal Membrane ◽

Renal Brush Border Membrane ◽

Proximal Tubular ◽

Renal Brush Border

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.

Download Full-text