Mechansims and components of renal tubular acidification.

Cassola, Antônio Carlos; Giebisch, Gerhard; Malnic, Gerhard

doi:10.1113/jphysiol.1977.sp011828

Cited by 28 publications

(12 citation statements)

References 26 publications

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“…Both were markedly altered at peritubular CO2 concentrations higher than 2 %. The effect of increasing CO2 on acidification half-times has been noted before (Mello Aires & Malnic, 1975) and has been attributed to an increased H ion conductance in the context of a proton pump leak model for proximal convoluted tubules (Cassola, Giebisch & Malnic, 1977) (see below).…”

Section: Factors In Tubular Acidification As Is Shown Inmentioning

confidence: 84%

Factors affecting proximal tubular acidification of non‐bicarbonate buffer in the rat.

Amorena¹,

Fernandes²,

Malnic³

1984

The Journal of Physiology

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SUMMARY1. The effect of peritubular PCO2 and pH changes within the physiological range on proximal tubular acidification ofnon-bicarbonate (phosphate) buffer was evaluated with and without carbonic anhydrase inhibition by stopped-flow microperfusion and Sb micro-electrode techniques.2. Luminal steady-state pH was reduced from 6-69 to 6-37 and H ion fluxes (JH+)increased from 0-63 to 1-57 nmol cm-2 s-1 by increasing capillary CO2 from 0 to 9-6 % at pH 7-2. 3. After acetazolamide a marked, although attenuated, effect ofCO2 on acidification was still observed; JH+ increased from 0-088 nmol cm-2 s-1 at 0 % CO2 to 0-78 at 9-6% CO2. Most of this effect can be explained by titration of luminal buffer by C02, uncatalysed CO2 hydration and H2CO3 recirculation.4. An increase in capillary CO2 reduced acidification half-times (t/2), which, according to an analogue circuit model, may be due to increased H ion access to the pump.5. Peritubular pH changes at 0 % CO2 also modified tubular acidification, increasing JH+ from 0-73 nmol cm-2 s-1 at pH 7-6 to 0 99 at pH 7 0. After acetazolamide, JH+ still increased from 0.11 nmol cm-2 s-1 at pH 7-6 to 0 57 at pH 7 0. 6. In conclusion, both peritubular C02 changes at constant pH and pH changes at 0 % C02 were effective to modify JH+, in the presence and absence of carbonic anhydrase activity. In the studied range, capillary C02 induced larger changes in JH+ than pH. The data show substrate (H ion) is a limiting factor for tubular H ion secretion.

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Section: Factors In Tubular Acidification As Is Shown Inmentioning

confidence: 84%

Factors affecting proximal tubular acidification of non‐bicarbonate buffer in the rat.

Amorena¹,

Fernandes²,

Malnic³

1984

The Journal of Physiology

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“…One way may be simply by limiting the tCO2 filtered load. Another could be that if the end-proxiInal [tCO2] in volume contraction represents a steady-state concentration of a balanced pump-leak system (40), it may be that acidosis directly augments or resets the pump activity responsible for hydrogen secretion or diminishes the backward leak. For instance, hydrogen ion secretion may be limited by a maxiimium transepithelial pH gradient as occuLrs in the distal nephron (41).…”

Section: Isohydric Ecf Expansionmentioning

confidence: 99%

“…After the plasma expansion period in group III, the hydropenia period in groups IV and VII, or an equivalent time in group VI, isotonic solutions were infused at 250 ,ul/min until 10% body wt was attained, followed by a sustaining infusion of 100 ,ul/min. After an equilibration period of [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] min, micropuncture was performed along with blood sampling and urine collections.…”

Section: Introductionmentioning

confidence: 99%

Control of Proximal Bicarbonate Reabsorption in Normal and Acidotic Rats

Cogan¹,

Maddox²,

Lucci³

et al. 1979

J. Clin. Invest.

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A B S T R A C T This free-flow micropuncture study examined the dependence ofbicarbonate reabsorption in the rat superficial proximal convoluted tubule to changes in filtered bicarbonate load, and thereby the contribution of the proximal tubule to the whole kidney's response to such changes. The independent effects of extracellular fluid (ECF) volume expansion and of acidosis on proximal bicarbonate reabsorption were also examined.When the plasma volume contraction incurred by the micropuncture preparatory surgery was corrected by isoncotic plasma infusion (-1.3% body wt), single nephron glomerular filtration rate (SNGFR), and the filtered total CO2 load increased by 50%. Absolute proximal reabsorption oftotal CO2 (measured by microcalorimetry) increased by 30%, from 808+47 during volume contraction to 1,081+57 pmol/min g kidney wt after plasma repletion, as fractional total CO2 reabsorption decreased from 0.90 to 0.77. Aortic constriction in these plasma-repleted rats returned the filtered load and reabsorption of total CO2 to the previous volume contracted levels. In other animals isohydric ECF expansion with plasma (5% body wt) or Ringer's solution (10% body wt), or both, produced no further diminution in fractional proximal total CO2 reabsorption (0.76-0.81).Metabolic acidosis was associated with very high fractional proximal total CO2 reabsorptive rates of 0.82 to 0.91 over a wide range of SNGFR and ECF volumes.Portions ofthis work were presented at the VII International

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“…Detailed treatments of this model have been published previously [21, 22, 23, 24]. Net H + secretion (J H + ) was calculated as:…”

Section: Methodsmentioning

confidence: 99%

Intrarenal Renin-Angiotensin System Contributes to Tubular Acidification Adaptation following Uninephrectomy

Amorena

Damasco²,

Igarreta³

et al. 2000

Nephron Exp Nephrol

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Background/Aims: Reduction in renal mass by uninephrectomy induces a functional compensation in the remnant kidney. The activity of the angiotensin-converting enzyme (ACE) as well as renin mRNA in the proximal convoluted tubule (PCT) of uninephrectomized (UNx) rats increases. The aim of this work was to determine whether the increased activity of the local renin-angiotensin system (RAS) participates in the adaptation of renal function after uninephrectomy. Method: We utilized normal two-kidney (2K) and 3-week UNx rats to study the activity of the ACE in vesicles obtained from luminal membranes of proximal tubular cells and the acidification kinectics in PCTs using micropuncture techniques. Results: The converting enzyme activity was significantly larger in UNx (5.87 ± 0.69 nmol · min^–1 · mg protein^–1) than in 2K rats (2.43 ± 0.13 nmol · min^–1 · mg protein^–1; p < 0.05). The acidification rate constant (κ) in PCT of 2K rats was 0.18 ± 0.02 s^–1 and in UNx rats 0.30 ± 0.04 s^–1 (p < 0.001). In UNx rats, microperfusion with 10^–5 M ramipril or 10^–5 M losartan decreased κ to 0.19 ± 0.02 and 0.18 ± 0.02 s^–1, respectively, but had no effect on 2K rats. Luminal steady-state pH (pH_∞) was the same in 2K and UNx rats, and was not modified by addition of 10^–5 M ramipril or 10^–5 M losartan in both groups. The proximal H⁺ flux (J_H⁺), calculated from pH_∞ and κ, was 1.12 nmol · cm^–2 · s^–1 in 2K rats and, 1.77 nmol · cm^–2 · s^–1 in UNx rats (p < 0.001). In 2K rats, this value was not changed by 10^–5 M ramipril or 10^–5 M losartan, but in UNx rats J_H⁺ decreased 25 and 30% with ramipril or losartan, respectively (p < 0.001). Conclusions: These data suggest that the increase in the local RAS activity could be an adaptive change that contributes to maintain the homeostasis of body fluids after uninephrectomy.

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Mechansims and components of renal tubular acidification.

Cited by 28 publications

References 26 publications

Factors affecting proximal tubular acidification of non‐bicarbonate buffer in the rat.

Factors affecting proximal tubular acidification of non‐bicarbonate buffer in the rat.

Control of Proximal Bicarbonate Reabsorption in Normal and Acidotic Rats

Intrarenal Renin-Angiotensin System Contributes to Tubular Acidification Adaptation following Uninephrectomy

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