Effects of metabolic acidosis on proximal tubule ion reabsorption in dog kidney

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.

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Basolateral membrane H-OH-HCO3 transport in the proximal tubule

AJP Renal Physiology ◽

10.1152/ajprenal.1989.256.5.f751 ◽

1989 ◽

Vol 256 (5) ◽

pp. F751-F765

Author(s):

P. A. Preisig ◽

R. J. Alpern

Keyword(s):

Metabolic Acidosis ◽

Proximal Tubule ◽

Basolateral Membrane ◽

Respiratory Acidosis ◽

Cell Voltage ◽

Transport Mechanisms ◽

Transport Capacity ◽

Chronic Metabolic Acidosis

This review focuses on the basolateral membrane mechanisms of H-OH-HCO3 transport in the proximal tubule. The mechanism that has the greatest transport capacity and mediates most of transepithelial H-HCO3 transport is the electrogenic, Na-3HCO3 cotransporter. This transporter has been extensively characterized in the salamander, rat, and rabbit proximal tubule, and has now been found in a number of other epithelia that effect transepithelial NaHCO3 transport. Transporter rate is sensitive to intra- and extracellular [Na], intra- and extracellular [HCO3]/pH, and cell voltage. Adaptations in transporter activity have been demonstrated in chronic metabolic acidosis and alkalosis, chronic respiratory acidosis and alkalosis, and chronic hyperfiltration. In addition to the Na-3HCO3 cotransporter, the basolateral membrane possesses both Na-dependent and -independent Cl-HCO3 exchangers, a H leak, and in the S3 proximal tubule an Na-H antiporter. The role of these H-OH-HCO3 transport mechanisms in transcellular HCO3 and Cl absorption and pHi defense is discussed.

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

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1984.247.5.e616 ◽

1984 ◽

Vol 247 (5) ◽

pp. E616-E624 ◽

Cited By ~ 3

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.

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High affinity phlorizin receptor sites and their relation to the glucose transport mechanism in the proximal tubule of dog kidney

Biochimica et Biophysica Acta (BBA) - Biomembranes ◽

10.1016/0005-2736(75)90201-1 ◽

1975 ◽

Vol 394 (1) ◽

pp. 10-30 ◽

Cited By ~ 53

Author(s):

Melvin Silverman ◽

Judith Black

Keyword(s):

Proximal Tubule ◽

Glucose Transport ◽

Transport Mechanism ◽

High Affinity ◽

Receptor Sites ◽

Dog Kidney

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Renal ATP Citrate Lyase (ATP CL) Protein Localizes throughout the Nephron and Increases Only in the Proximal Tubule with Chronic Metabolic Acidosis (CMA)

Pediatric Research ◽

10.1203/00006450-199904020-01996 ◽

1999 ◽

Vol 45 (4, Part 2 of 2) ◽

pp. 336A-336A

Author(s):

Krishna Puttaparthi ◽

Thomas Rogers ◽

Nabil A Elshourbagy ◽

Moshe Levi ◽

Joel Z Melnick

Keyword(s):

Metabolic Acidosis ◽

Proximal Tubule ◽

Atp Citrate Lyase ◽

Chronic Metabolic Acidosis ◽

Citrate Lyase

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Effects of acid-base disturbances on renal handling of magnesium in the dog

Clinical Science ◽

10.1042/cs0700277 ◽

1986 ◽

Vol 70 (3) ◽

pp. 277-284 ◽

Cited By ~ 21

Author(s):

Norman L. M. Wong ◽

Gary A. Quamme ◽

John H. Dirks

Keyword(s):

Metabolic Acidosis ◽

Proximal Tubule ◽

Indirect Effect ◽

Metabolic Alkalosis ◽

Distal Tubule ◽

Acid Base ◽

Renal Handling ◽

Chronic Metabolic Acidosis ◽

Magnesium Transport

1. Clearance and micropuncture studies were performed in four groups of acutely thyropara-thyroidectomized animals to study the effects of alkalosis and acidosis on the renal handling of magnesium. 2. Our results indicate that chronic metabolic acidosis reduces, whereas acute metabolic alkalosis enhances, magnesium reabsorption. 3. The site within the nephron where absorption of magnesium increases or decreases during acid-base disturbances was beyond the late proximal tubule. 4. Tubular fluid bicarbonate was also measured in these experiments, and the results indicated that magnesium reabsorption in the distal tubule correlated to bicarbonate delivery. However, whether this was a direct or an indirect effect of bicarbonate on magnesium transport could not be delineated.

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