Increased Vmax for Na+/H+ antiporter activity in proximal tubule brush border vesicles from rabbits with metabolic acidosis

1984 ◽  
Vol 247 (2) ◽  
pp. F339-F343 ◽  
Author(s):  
C. J. Tsai ◽  
H. E. Ives ◽  
R. J. Alpern ◽  
V. J. Yee ◽  
D. G. Warnock ◽  
...  
Keyword(s):  
Metabolic Acidosis ◽  
Proximal Tubule ◽  
Cation Exchange ◽  
Acridine Orange ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Co2 Concentration ◽  
Chronic Metabolic Acidosis ◽  
Experimental Animals ◽  
Renal Brush Border

Na+/H+ antiporter activity in renal brush border vesicles from control rabbits and rabbits made acidotic with 3 days of NH4Cl gavage was measured using the acridine orange method. Acidotic rabbits exhibited a significantly higher Vmax for antiporter activity (2.80 +/- 0.45 fluorescence units X s-1 X mg protein-1) compared with controls (1.31 +/- 0.13) but the Km for Na+ was unchanged (23.7 +/- 3.5 for acidotic, 19.1 +/- 3.2 mM for controls). When the Vmax for Na+/H+ antiporter activity was considered in relation to the degree of acidosis achieved in the experimental animals, there was a correlation (r = -0.75) between Vmax and plasma total CO2 concentration. Amiloride (100 microM) inhibited Na+/H+ exchange (Na+ = 90 mM) by 59 +/- 7% in both control and acidotic animals, indicating that the observed stimulation in Na+/H+ antiporter activity was not due to increased electrically coupled cation exchange. These findings suggest that the response of the proximal tubule to chronic metabolic acidosis involves an adaptive increase in the Vmax for Na+/H+ antiporter activity in the brush border membrane that is correlated to the degree of acidosis in the animals.

Metabolic acidosis and parathyroidectomy increase Na+-H+ exchange in brush border vesicles

1983 ◽  
Vol 245 (2) ◽  
pp. F217-F222 ◽  
Author(s):  
D. E. Cohn ◽  
S. Klahr ◽  
M. R. Hammerman
Keyword(s):  
Metabolic Acidosis ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Chronic Metabolic Acidosis ◽  
Renal Brush Border Membrane ◽  
Dog Kidney ◽  
Renal Proximal Tubular ◽  
Renal Brush Border

Na+-H+ exchange across the brush border membrane of the renal proximal tubular cell is a mechanism for Na+ reabsorption and H+ secretion. An electroneutral Na+-H+ exchange activity has been identified in isolated renal brush border membrane vesicles from rat and dog kidney, and increased Na+-H+ exchange has been measured in brush border membrane vesicles from remnant kidneys of dogs with chronic renal failure. To ascertain whether changes in H+ secretion by the kidney observed in chronic metabolic acidosis and in states of altered parathyroid function might result from altered Na+-H+ exchange across the renal cortical cellular brush border membrane, we measured Na+-H+ exchange in brush border membrane vesicles from kidneys of dogs with chronic metabolic acidosis and from kidneys of thyroparathyroidectomized dogs. Increased amiloride-sensitive Na+-H+ exchange was demonstrated in brush border membrane vesicles from kidneys of both groups of dogs, suggesting that adaptations in H+ excretion in chronic metabolic acidosis and hypoparathyroidism might be explained by increased activity of a renal brush border membrane Na+-H+ exchanger.

scholarly journals Effect of dietary phosphate intake on phosphate transport by isolated rat renal brush-border vesicles

1979 ◽  
Vol 180 (3) ◽  
pp. 465-470 ◽  
Author(s):  
Reinhard Stoll ◽  
Rolf Kinne ◽  
Heini Murer
Keyword(s):  
Proximal Tubule ◽  
Brush Border ◽  
Dry Matter ◽  
Brush Border Membrane ◽  
Phosphate Uptake ◽  
Membrane Vesicles ◽  
Phosphate Transport ◽  
Phosphate Intake ◽  
Dietary Phosphate ◽  
Renal Brush Border

Renal brush-border membrane vesicles isolated from rats kept for 6–8 weeks on a low-phosphate diet (0.15% of dry matter) showed a markedly faster Na+-dependent phosphate uptake than did membrane vesicles isolated from animals kept on a high-phosphate diet (2% of dry matter). Phosphate-uptake rate by brush-border membrane vesicles isolated from animals on a low-phosphate diet remained significantly increased after acute parathyroidectomy. Dietary adaptation was also observed in animals that had been parathyroidectomized before exposure to the different diets. In animals on the low-phosphate diet parathyrin administration inhibited phosphate uptake by brush-border vesicles only if the animals were repleted with Pi (5ml of 20mm-NaH2PO4) 1h before being killed. After acute phosphate loading and parathyrin administration the difference in the transport rate between the two dietary groups remained statistically significant. The results suggest that the adaptation of proximal-tubule phosphate transport to dietary intake of phosphate is reflected in the Na+/phosphate co-transport system located in the luminal membrane of the proximal-tubule cell. Since the dietary effects on phosphate transport by brush-border membranes are only partially reversed by acute changes in parathyrin concentration and are also observed in chronically parathyroidectomized animals, the adaptation of the Na+/phosphate co-transport system to dietary phosphate intake seems to involve an additional mechanism independent of parathyrin.

scholarly journals Effect of metabolic acidosis on neonatal proximal tubule acidification

2010 ◽  
Vol 299 (5) ◽  
pp. R1360-R1368 ◽  
Author(s):  
Katherine Twombley ◽  
Jyothsna Gattineni ◽  
Ion Alexandru Bobulescu ◽  
Vangipuram Dwarakanath ◽  
Michel Baum
Keyword(s):  
Metabolic Acidosis ◽  
Proximal Tubule ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Protein Abundance ◽  
Serum Bicarbonate ◽  
Neonatal Rats ◽  
Neonatal Mice ◽  
Maximal Capacity

The serum bicarbonate in neonates is lower than adults due in large part to a lower rate of proximal tubule acidification. It is unclear if the neonatal proximal tubule is functioning at maximal capacity or if the proximal tubule can respond to metabolic acidosis as has been described in adult proximal tubules. We find that neonatal mouse brush-border membranes have a lower Na+/H+ exchanger (NHE) 3 protein abundance (neonate 0.11 ± 0.05 vs. adult 0.64 ± 0.07; P < 0.05) and a higher NHE8 protein abundance (neonate 1.0 ± 0.01 vs. adult 0.13 ± 0.09; P < 0.001) compared with adults. To examine if neonates can adapt to acidosis, neonatal mice were gavaged with either acid or vehicle for 4 days, resulting in a drop in serum bicarbonate from 19.5 ± 1.0 to 8.9 ± 0.6 meq/l ( P < 0.001). Proximal convoluted tubule Na+/H+ exchanger activity (dpHi/d t) was 1.68 ± 0.19 pH units/min in control tubules and 2.49 ± 0.60 pH units/min in acidemic neonatal mice ( P < 0.05), indicating that the neonatal proximal tubule can respond to metabolic acidosis with an increase in Na+/H+ exchanger activity. Similarly, brush-border membrane vesicles from neonatal rats had an increase in Na+/H+ exchanger activity with acidemia that was almost totally inhibited by 10−6 M 5-( N-ethyl- n-isopropyl)-amiloride, a dose that has little effect on NHE3 but inhibits NHE8. There was a significant increase in both NHE3 (vehicle 0.35 ± 0.07 vs. acid 0.73 ± 0.07; P < 0.003) and NHE8 brush-border membrane protein abundance (vehicle 0.41 ± 0.05 vs. acid 0.73 ± 0.06; P < 0.001) in acidemic mouse neonates compared with controls. A comparable increase in NHE3 and NHE8 was found in neonatal rats with acidosis. In conclusion, the neonatal proximal tubule can adapt to metabolic acidosis with an increase in Na+/H+ exchanger activity.

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

1989 ◽  
Vol 257 (5) ◽  
pp. C971-C975 ◽  
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.

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