Effect of metabolic acidosis on proximal tubular total CO2 absorption

1985 ◽  
Vol 249 (1) ◽  
pp. F62-F68 ◽  
Author(s):  
R. T. Kunau ◽  
J. I. Hart ◽  
K. A. Walker
Keyword(s):  
Metabolic Acidosis ◽  
Proximal Tubule ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Co2 Absorption ◽  
Arterial Blood ◽  
Blood Ph ◽  
In Series ◽  
Proximal Tubular

In vivo microperfusion studies of the proximal convoluted tubule of the rat were performed to determine the effect of metabolic acidosis on total CO2 (tCO2) absorption. In series I, tubular perfusion was performed in control and acidotic rats in a manner by which similar mean total CO2 concentrations in the proximal tubule were maintained. Comparable ranges of perfusion rate were studied in both groups. Following 3 days of HCl ingestion, plasma tCO2 was 20.0 +/- 0.9 mM in the acidotic rats whereas it was 29.6 +/- 0.53 mM in control rats. The arterial blood pH values were 7.25 +/- 0.02 vs. 7.43 +/- 0.01. Starting tCO2 perfusate concentrations were identical in both groups, 29.3 and 29.7 mM, as were the concentrations at the end of the perfused segments, 21.2 and 21.9 mM. The absorption of tCO2 (JtCO2, pmol X mm-1 X min-1) was significantly greater in the acidotic rats than in the controls, 576 +/- 39 vs. 256 +/- 21. At all perfusion rates studied, proximal tubular JtCO2 was higher in the acidotic than in the control rats. In series II, similar lengths of the late proximal tubule were perfused at the same rate in control and acidotic rats. Again, JtCO2 was higher in the acidotic rats, 352 +/- 19 vs. 198 +/- 13. The results indicate that at comparable luminal tCO2 concentration and tubular fluid flow rates, tCO2 absorption is significantly increased in the acidotic state. Although other mechanisms cannot be excluded, the finding of an increase in proximal tCO2 absorption in the acidotic rats is in agreement with the presence of an accelerated Na+/H+ exchange rate in brush border membrane vesicles obtained from the renal cortex of animals with metabolic acidosis.

Insulin stimulates Pi transport in brush border vesicles from proximal tubular segments

1984 ◽  
Vol 247 (5) ◽  
pp. E616-E624 ◽  
Author(s):  
M. R. Hammerman ◽  
S. Rogers ◽  
V. A. Hansen ◽  
J. R. Gavin
Keyword(s):  
Proximal Tubule ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Direct Action ◽  
Membrane Vesicles ◽  
Pi Transport ◽  
Glomerular Filtrate ◽  
Dog Kidney ◽  
Proximal Tubular ◽  
Altered Transport

Induction of hyperinsulinemia in dogs results in enhanced reabsorption of Pi from glomerular filtrate in the renal proximal tubule. To determine whether this may be a direct action of insulin mediated by altered transport characteristics of the proximal tubular brush border membrane, we measured Na+-dependent 32Pi transport in brush border membrane vesicles prepared from isolated proximal tubular segments originating from dog kidney that had been incubated with or without insulin. Specific high affinity binding sites for insulin were detected in proximal tubular segments. Increased initial rates (15 s) of Na+-dependent 32Pi transport were measured in brush border vesicles prepared from segments that had been incubated with insulin. This effect of insulin was concentration dependent over the range of 10(-10) to 10(-6) M insulin. These studies demonstrate the feasibility of using brush border vesicles prepared from proximal tubular segments to study solute transport. Our findings suggest that insulin-induced increased Pi reabsorption in the proximal tubule is mediated by a direct action of insulin on the proximal tubular cell, which results in increased Na+-Pi cotransport across the brush border membrane.

31P-NMR in vivo measurement of renal intracellular pH: effects of acidosis and K+ depletion in rats

1986 ◽  
Vol 251 (5) ◽  
pp. F904-F910 ◽  
Author(s):  
W. R. Adam ◽  
A. P. Koretsky ◽  
M. W. Weiner
Keyword(s):  
Metabolic Acidosis ◽  
Intracellular Ph ◽  
Respiratory Acidosis ◽  
Resonance Spectroscopy ◽  
Ph Effects ◽  
Potassium Depletion ◽  
Chronic Metabolic Acidosis ◽  
Arterial Blood ◽  
Blood Ph

Renal intracellular pH (pHi) was measured in vivo from the chemical shift (sigma) of inorganic phosphate (Pi), obtained by 31P-nuclear magnetic resonance spectroscopy (NMR). pH was calculated from the difference between sigma Pi and sigma alpha-ATP. Changes of sigma Pi closely correlated with changes of sigma monophosphoesters; this supports the hypothesis that the pH determined from sigma Pi represents pHi. Renal pH in control rats was 7.39 +/- 0.04 (n = 8). This is higher than pHi of muscle and brain in vivo, suggesting that renal Na-H antiporter activity raises renal pHi. To examine the relationship between renal pH and ammoniagenesis, rats were subjected to acute (less than 24 h) and chronic (4-7 days) metabolic acidosis, acute (20 min) and chronic (6-8 days) respiratory acidosis, and dietary potassium depletion (7-21 days). Acute metabolic and respiratory acidosis produced acidification of renal pHi. Chronic metabolic acidosis (arterial blood pH, 7.26 +/- 0.02) lowered renal pHi to 7.30 +/- 0.02, but chronic respiratory acidosis (arterial blood pH, 7.30 +/- 0.05) was not associated with renal acidosis (pH, 7.40 +/- 0.04). At a similar level of blood pH, pHi was higher in chronic metabolic acidosis than in acute metabolic acidosis, suggesting an adaptive process that raises pHi. Potassium depletion (arterial blood pH, 7.44 +/- 0.05) was associated with a marked renal acidosis (renal pH, 7.17 +/- 0.02). There was a direct relationship between renal pH and cardiac K+. Rapid partial repletion with KCl (1 mmol) significantly increased renal pHi from 7.14 +/- 0.03 to 7.31 +/- 0.01.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of the Na+-H+ antiporter in the intact renal proximal tubular cell

1986 ◽  
Vol 250 (3) ◽  
pp. F539-F550 ◽  
Author(s):  
E. P. Nord ◽  
D. Goldfarb ◽  
N. Mikhail ◽  
P. Moradeshagi ◽  
A. Hafezi ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Intact Cell ◽  
Membrane Vesicles ◽  
Renal Proximal Tubule ◽  
Brush Border Membrane Vesicles ◽  
Intact Cells ◽  
Proximal Tubular ◽  
Internal Site

The characteristics of the proximal tubular Na+-H+ antiporter were determined in isolated proximal tubular cells to ascertain whether the features of this transport system in intact cells are comparable with those previously described for isolated brush-border membrane vesicles. A method is described for the rapid isolation of a purified preparation of cells that demonstrate morphological and functional characteristics of the renal proximal tubule. The cells maintain their polarity while in suspension, and adenylate cyclase activity is enhanced by parathyroid hormone but not by arginine vasopressin. The cells display gluconeogenic function and Na+-dependent alpha-methyl-D-glucose and organic phosphate cotransport, processes that confirm their proximal tubule origin. O2 consumption rates and cytosolic adenosine triphosphate levels indicate functional integrity. Na+-H+ antiport activity was defined in these cells by measuring amiloride-sensitive Na+ uptake. At intracellular pH = 6.4 vs. extracellular pH = 7.4, KtNa was 10.1 +/- 2.8 mM, and maximal sodium flux was 0.89 +/- 0.13 nmol X 10(6) cells-1 X K0.5 for amiloride and ethyl-isopropyl amiloride, measured at an external Na+ concentration of 1 mM, was observed at 2.5 X 10(-5) M and 2.9 X 10(-6) M, respectively. The external and internal loci of the exchanger displayed asymmetric affinity for the hydrogen ion: the apparent pK for the external site was 7.20-7.26 vs. less than 6.5 for the internal site. The internal site demonstrated features of positive cooperativity. In summary, the Na+-H+ antiporter present in the luminal membrane of the renal proximal tubule has been characterized in the intact cell and displays functional and kinetic parameters closely resembling those described in isolated brush-border membrane vesicles.

Amiloride inhibition of proximal tubular acidification

1985 ◽  
Vol 248 (6) ◽  
pp. F773-F778 ◽  
Author(s):  
K. J. Howlin ◽  
R. J. Alpern ◽  
F. C. Rector
Keyword(s):  
Brush Border Membrane ◽  
Potent Inhibitor ◽  
Membrane Vesicles ◽  
Kidney Cortex ◽  
Volume Flux ◽  
Perfusion Rate ◽  
Volume Absorption ◽  
Chloride Absorption ◽  
Proximal Tubular

In brush border membrane vesicles prepared from mammalian kidney cortex, amiloride is a potent inhibitor of the Na+/H+ exchanger. In the present study, in vivo microperfusion was used to examine the effect of luminal amiloride on transport in the rat superficial proximal convoluted tubule. At a perfusion rate of 14 nl/min, addition of 10(-3) M amiloride to artificial early proximal tubular fluid reduced bicarbonate absorption from 103 +/- 7 to 81 +/- 5 pmol mm-1 X min-1 and volume absorption from 2.03 +/- 0.15 to 1.57 +/- 0.06 nl X mm-1 X min-1. Glucose efflux was unchanged, excluding nonspecific inhibition of Na+-K+-ATPase. Luminal amiloride at 10(-4) M did not affect bicarbonate absorption or volume absorption. At a perfusion rate of 41 nl/min, 10(-3) M amiloride reduced bicarbonate absorption from 179 +/- 8 to 114 +/- 9 pmol X mm-1 X min-1, a significantly greater inhibition than that seen in tubules perfused at 14 nl/min. Amiloride at 10(-3) M had no significant effect on sodium chloride absorption as measured by volume flux from an artificial late proximal tubular fluid. The results show that luminal amiloride specifically inhibits proximal acidification and demonstrate involvement of the Na+/H+ antiporter in proximal tubular acidification. However, the inhibition of acidification is less than the inhibition of Na+/H+ exchange predicted by vesicle studies.

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.

Potential differences influence amino acid/Na+ symport rates in larval Manduca sexta midgut brush-border membrane vesicles.

1994 ◽  
Vol 189 (1) ◽  
pp. 55-67
Author(s):  
R Parthasarathy ◽  
W R Harvey
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Manduca Sexta ◽  
Brush Border ◽  
Brush Border Membrane ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Rate Determining Step ◽  
Half Saturation Constant

The time-dependent fluorescence intensity of an intravesicular potential-sensitive dye was used to probe the real-time kinetics of potential difference (PD)-dependent amino acid/Na+ symport at pH9 into brush-border membrane vesicles obtained from larval Manduca sexta midgut. Neutral amino acids (alanine, proline) are symported at higher rates as the vesicles are hyperpolarized. The symport rates of acidic (glutamate) and basic (arginine) amino acids are almost PD-independent. The half-saturation constant of alanine is PD-independent between -108 and -78 mV, although the maximal symport velocity increases by half as the voltage is increased. Amino acid throughput is evidently enhanced as the relatively high transmembrane PDs (&gt; 150 mV, lumen positive) measured in vivo are approached. The half-saturation concentrations of Na+ were in the range 15-40 mmol l-1 for most of the amino acids examined and increased with voltage for alanine. The Vmax observed as a function of cation or amino acid concentration increased as the vesicle was hyperpolarized in the case of leucine and alanine. The data support the hypothesis that carrier and substrates are at equilibrium inasmuch as substrate translocation seems to be the rate-determining step of symport.

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