scholarly journals Acetazolamide causes renal HCO3− wasting but inhibits ammoniagenesis and prevents the correction of metabolic acidosis by the kidney

2020 ◽  
Vol 319 (3) ◽  
pp. F366-F379
Author(s):  
Perwez Alam ◽  
Sihame Amlal ◽  
Charuhas V. Thakar ◽  
Hassane Amlal
Keyword(s):  
Metabolic Acidosis ◽  
Carbonic Anhydrase ◽  
Proximal Tubule ◽  
Glutamate Dehydrogenase ◽  
Ammonia Synthesis ◽  
Similar Degree ◽  
Protein Abundance ◽  
Text Generation ◽  
Glutamine Transporter ◽  
Renal Adaptation

Carbonic anhydrase (CAII) binds to the electrogenic basolateral Na+-[Formula: see text] cotransporter (NBCe1) and facilitates [Formula: see text] reabsorption across the proximal tubule. However, whether the inhibition of CAII with acetazolamide (ACTZ) alters NBCe1 activity and interferes with the ammoniagenesis pathway remains elusive. To address this issue, we compared the renal adaptation of rats treated with ACTZ to NH4Cl loading for up to 2 wk. The results indicated that ACTZ-treated rats exhibited a sustained metabolic acidosis for up to 2 wk, whereas in NH4Cl-loaded rats, metabolic acidosis was corrected within 2 wk of treatment. [Formula: see text] excretion increased by 10-fold in NH4Cl-loaded rats but only slightly (1.7-fold) in ACTZ-treated rats during the first week despite a similar degree of acidosis. Immunoblot experiments showed that the protein abundance of glutaminase (4-fold), glutamate dehydrogenase (6-fold), and SN1 (8-fold) increased significantly in NH4Cl-loaded rats but remained unchanged in ACTZ-treated rats. Na+/H+ exchanger 3 and NBCe1 proteins were upregulated in response to NH4Cl loading but not ACTZ treatment and were rather sharply downregulated after 2 wk of ACTZ treatment. ACTZ causes renal [Formula: see text] wasting and induces metabolic acidosis but inhibits the upregulation of glutamine transporter and ammoniagenic enzymes and thus suppresses ammonia synthesis and secretion in the proximal tubule, which prevented the correction of acidosis. This effect is likely mediated through the inhibition of the CA-NBCe1 metabolon complex, which results in cell alkalinization. During chronic ACTZ treatment, the downregulation of both NBCe1 and Na+/H+ exchanger 3, along with the inhibition of ammoniagenesis and [Formula: see text] generation, contributes to the maintenance of metabolic acidosis.

Cortisol alters carbonic anhydrase-mediated renal sulfate secretion

2003 ◽  
Vol 285 (6) ◽  
pp. R1430-R1438 ◽  
Author(s):  
Ryan M. Pelis ◽  
James E. Goldmeyer ◽  
Joseph Crivello ◽  
J. Larry Renfro
Keyword(s):  
Carbonic Anhydrase ◽  
Proximal Tubule ◽  
Plasma Membranes ◽  
Sequence Similarity ◽  
Renal Proximal Tubule ◽  
Protein Abundance ◽  
High Sequence Similarity ◽  
Partial Cdna ◽  
Partial Cdna Clone ◽  
Low Cortisol

Active transepithelial sulfate secretion rate by winter flounder renal proximal tubule epithelium in primary culture (fPTC) is dependent on intracellular carbonic anhydrase (CA) and enhanced by cortisol. To further evaluate this relationship, a partial cDNA clone (327 bp) of carbonic anhydrase II (CAII) with high sequence similarity to CAII from numerous species including fish, chicken, and human was obtained from fPTCs. The majority of CA activity and CAII protein was present in the cytosol of fPTCs; however, significant amounts of both (in addition to SDS-resistant CA activity, i.e., CAIV-like isoform) were present in concentrated plasma membranes. CAII from concentrated membranes migrated differently than purified CAII on nondenaturing PAGE gels, suggesting that CAII associates with another membrane component. Treatment of fPTCs with the cell-soluble CA inhibitor methazolamide (100 μM) caused a 58% reduction in active transepithelial SO42- secretion. fPTCs that were previously cultured under high-cortisol concentrations, when subjected to 5 days of low physiological levels of cortisol, had decreased CA activity (28%), CAII protein abundance (65%), and net active SO42- secretion (28%), with no effect on epithelial differentiation. Methazolamide and low-cortisol treatment in combination inhibited net active SO42- secretion 56%, which was not different than the effect of methazolamide treatment alone. These data indicate that cortisol directly increases renal CA activity, CAII protein abundance, and CA-dependent SO42- secretion in the marine teleost renal proximal tubule.

Stimulation of renal sulfate secretion by metabolic acidosis requires Na+/H+ exchange induction and carbonic anhydrase

2005 ◽  
Vol 289 (1) ◽  
pp. F208-F216 ◽  
Author(s):  
Ryan M. Pelis ◽  
Susan L. Edwards ◽  
Stan C. Kunigelis ◽  
James B. Claiborne ◽  
J. Larry Renfro
Keyword(s):  
Metabolic Acidosis ◽  
Carbonic Anhydrase ◽  
Proximal Tubule ◽  
Brush Border ◽  
Primary Cultures ◽  
Acute Effect ◽  
Renal Proximal Tubule ◽  
Ussing Chambers ◽  
Renal Tubular ◽  
Nhe Isoforms

The acute effect of metabolic acidosis on SO42− secretion by the marine teleost renal proximal tubule was examined. Metabolic acidosis was mimicked in primary cultures of winter flounder renal proximal tubule epithelium (fPTCs) mounted in Ussing chambers by reducing interstitial pH to 7.1 (normally 7.7). fPTCs with metabolic acidosis secreted SO42− at a net rate that was 40% higher than in paired isohydric controls (pH 7.7 on interstitium). The stimulation was completely blocked by the carbonic anhydrase inhibitor methazolamide (100 μM). Although Na+/H+ exchange (NHE) isoforms 1, 2, and 3 were identified in fPTCs by immunoblotting, administering EIPA (20 μM) to the interstitial and luminal bath solutions had no effect on net SO42− secretion by fPTCs with a normal interstitial pH of 7.7. However, EIPA (20 μM) blocked most of the stimulation caused by acidosis when applied to the lumen but not interstitium, demonstrating that induction of brush-border NHE activity is important. In the intact flounder, serum pH dropped 0.4 pH units (pH 7.7 to 7.3, at 2–3 h) when environmental pH was lowered from 7.8 to ∼4.3. Whereas serum [SO42−] was not altered by acidosis, renal tubular SO42− secretion rate was elevated 200%. Thus metabolic acidosis strongly stimulates renal sulfate excretion most likely by a direct effect on active renal proximal tubule SO42− secretion. This stimulation appears to be dependent on inducible brush-border NHE activity.

Chronic metabolic acidosis increases NHE3 protein abundance in rat kidney

1996 ◽  
Vol 271 (4) ◽  
pp. F917-F925 ◽  
Author(s):  
P. M. Ambuhl ◽  
M. Amemiya ◽  
M. Danczkay ◽  
M. Lotscher ◽  
B. Kaissling ◽  
...  
Keyword(s):  
Metabolic Acidosis ◽  
Proximal Tubule ◽  
Phosphoenolpyruvate Carboxykinase ◽  
Apical Membrane ◽  
Rat Kidney ◽  
Mrna Abundance ◽  
Thick Ascending Limb ◽  
Protein Abundance ◽  
Chronic Metabolic Acidosis ◽  
Apical Membranes

Chronic metabolic acidosis increases the activity of the proximal tubule apical membrane Na/H antiporter, which is encoded predominantly by the NHE3 isoform. The present studies examined the effect of chronic metabolic acidosis on apical membrane NHE3 protein abundance in rats. Rats subjected to NH4Cl in their drinking water developed a metabolic acidosis, which decreased in magnitude over 14 days. During this time, renal cortical brush-border membrane NHE3 protein abundance, assessed by Western blot, increased progressively (28% at 3 days, 59% at 7 days, and 90% at 14 days). Immunohistochemistry revealed that the acidosis-induced increase in NHE3 abundance occurred in the apical membranes of the S1 and S2 segments of the proximal tubule and the thick ascending limb. NHE3 mRNA abundance was not significantly increased in these animals, whereas phosphoenolpyruvate carboxykinase and glyceraldehyde-3-phosphate dehydrogenase mRNA abundances were significantly increased. These studies demonstrate that the increase in Na/H antiporter activity seen in metabolic acidosis involves an increase in NHE3 protein abundance, which is distributed along the proximal tubule and the thick ascending limb. In addition, these studies suggest that a component of this adaptation is unrelated to changes in NHE3 mRNA abundance.

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.

1123: Renal Oxalate Transport Depends on Local Carbonic Anhydrase Activity in the Proximal Tubule

2004 ◽  
Vol 171 (4S) ◽  
pp. 296-296
Author(s):  
Michael Straub ◽  
Joséphine Befolo-Elo ◽  
Richard E Hautmann ◽  
Edgar Braendle
Keyword(s):  
Carbonic Anhydrase ◽  
Proximal Tubule ◽  
Carbonic Anhydrase Activity ◽  
Oxalate Transport

Mitochondrial aquaporin-8 in renal proximal tubule cells: evidence for a role in the response to metabolic acidosis

2012 ◽  
Vol 303 (3) ◽  
pp. F458-F466 ◽  
Author(s):  
Sara M. Molinas ◽  
Laura Trumper ◽  
Raúl A. Marinelli
Keyword(s):  
Metabolic Acidosis ◽  
Protein Expression ◽  
Proximal Tubule ◽  
Ammonia Excretion ◽  
Renal Proximal Tubule ◽  
In Vivo Studies ◽  
Proximal Tubule Cell ◽  
Inner Mitochondrial Membrane ◽  
Ammonia Transport ◽  
In Cells

Mitochondrial ammonia synthesis in proximal tubules and its urinary excretion are key components of the renal response to maintain acid-base balance during metabolic acidosis. Since aquaporin-8 (AQP8) facilitates transport of ammonia and is localized in inner mitochondrial membrane (IMM) of renal proximal cells, we hypothesized that AQP8-facilitated mitochondrial ammonia transport in these cells plays a role in the response to acidosis. We evaluated whether mitochondrial AQP8 (mtAQP8) knockdown by RNA interference is able to impair ammonia excretion in the human renal proximal tubule cell line, HK-2. By RT-PCR and immunoblotting, we found that AQP8 is expressed in these cells and is localized in IMM. HK-2 cells were transfected with short-interfering RNA targeting human AQP8. After 48 h, the levels of mtAQP8 protein decreased by 53% ( P < 0.05). mtAQP8 knockdown decreased the rate of ammonia released into culture medium in cells grown at pH 7.4 (−31%, P < 0.05) as well as in cells exposed to acid (−90%, P < 0.05). We also evaluated mtAQP8 protein expression in HK-2 cells exposed to acidic medium. After 48 h, upregulation of mtAQP8 (+74%, P < 0.05) was observed, together with higher ammonia excretion rate (+73%, P < 0.05). In vivo studies in NH4Cl-loaded rats showed that mtAQP8 protein expression was also upregulated after 7 days of acidosis in renal cortex (+51%, P < 0.05). These data suggest that mtAQP8 plays an important role in the adaptive response of proximal tubule to acidosis possibly facilitating mitochondrial ammonia transport.

Effect of carbonic anhydrase inhibition on proximal tubular bicarbonate reabsorption

1963 ◽  
Vol 205 (4) ◽  
pp. 693-696 ◽  
Author(s):  
James R. Clapp ◽  
John F. Watson ◽  
Robert W. Berliner
Keyword(s):  
Carbonic Anhydrase ◽  
Proximal Tubule ◽  
Intravenous Administration ◽  
Distal Portion ◽  
Bicarbonate Concentration ◽  
Plasma Bicarbonate ◽  
Bicarbonate Reabsorption ◽  
Carbonic Anhydrase Inhibition ◽  
Before And After ◽  
Proximal Tubular

Samples of fluid from the proximal tubule were collected for the measurement of pH and bicarbonate concentration before and after the administration of acetazolamide (Diamox). Samples collected before acetazolamide were consistently more acid than plasma with the most acid samples coming from the more distal portion of the proximal tubule. After the intravenous administration of acetazolamide, the pH and bicarbonate concentration were consistently higher than in plasma. Bicarbonate concentrations as high as 2.8 times that in plasma were observed. The rise in proximal tubular fluid bicarbonate concentration after acetazolamide is presumably due to a reduction in the rate of bicarbonate reabsorption out of proportion to any impairment in proximal tubular fluid volume reduction.

NHE3 activity and trafficking depend on the state of actin organization in proximal tubule

2001 ◽  
Vol 280 (2) ◽  
pp. F283-F290 ◽  
Author(s):  
C. Chalumeau ◽  
D. Du Cheyron ◽  
N. Defontaine ◽  
O. Kellermann ◽  
M. Paillard ◽  
...  
Keyword(s):  
Proximal Tubule ◽  
Cortical Cell ◽  
Membrane Vesicles ◽  
Cytochalasin D ◽  
The State ◽  
Protein Abundance ◽  
Transport Activity ◽  
Cortical Cells ◽  
Actin Organization ◽  
Luminal Membrane

The present study was addressed to define the contribution of cytoskeleton elements in the kidney proximal tubule Na+/H+ exchanger 3 (NHE3) activity under basal conditions. We used luminal membrane vesicles (LMV) isolated from suspensions of rat cortical tubules pretreated with either colchicine (Colch) or cytochalasin D (Cyto D). Colch pretreatment of suspensions (200 μM for 60 min) moderately decreased LMV NHE3 activity. Cyto D pretreatment (1 μM for 60 min) elicited an increase in LMV NHE3 transport activity but did not increase Na-glucose cotransport activity. Cyto D pretreatment of suspensions did not change the apparent affinity of NHE3 for internal H+. In contrast, after Cyto D pretreatment of the suspensions, NHE3 protein abundance was increased in LMV and remained unchanged in cortical cell homogenates. The effect of Cyto D on NHE3 was further assessed with cultures of murine cortical cells. The amount of surface biotinylated NHE3 increased on Cyto D treatment, whereas NHE3 protein abundance was unchanged in cell homogenates. In conclusion, under basal conditions NHE3 activity depends on the state of actin organization possibly involved in trafficking processes between luminal membrane and intracellular compartment.

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