Acidification of phosphate buffer in cortical tubules of rat kidney

Malnic, Gerhard; Mello-Aires, Margarida; Mello, G. B. de; Giebisch, Gerhard

doi:10.1007/bf00589134

Cited by 12 publications

(6 citation statements)

References 3 publications

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“…sec-), and r is the luminal radius expressed in cm (Gertz, 1963;Malnic & Mello Aires, 1971;Malnic et al 1972b). Fig.…”

Section: Methodsmentioning

confidence: 99%

“…The present study deals with a quantitative analysis of intratubular titratable acid formation and compares the latter with bicarbonate reabsorption. Stationary microperfusion methods were combined with continuous measurements of pH changes of luminally deposited buffers (Malnic & Mello Aires, 1971; Malnic, Mello Aires, de Mello & Giebisch, 1972b). This approach offers some advantages over free-flow measurements of acid-base parameters in buffer-loaded animals.…”

Section: Introductionmentioning

confidence: 99%

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Kinetics of luminal acidification in cortical tubules of the rat kidney.

Giebisch¹,

Malnic²,

Mello³

et al. 1977

The Journal of Physiology

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2. Experiments were performed in control rats, in animals undergoing metabolic acidosis or alkalosis and in control and acidotic rats receiving the carbonic anydrase inhibitor Diamox. 3. In all experiments, the rates of tubular bicarbonate reabsorption and of phosphate acidification (H ion secretion) were proportional to luminal buffer levels. The change of luminal acid concentrations followed first-order kinetics.4. Steady-state transepithelial pH differences were reduced in metabolic alkalosis and after diamox but augmented during metabolic acidosis.5. Acidification half-times were prolonged in metabolic acidosis and after Diamox but remained similar to control levels in metabolic alkalosis.6. From the observation that both bicarbonate reabsorption and * Supported by grants from Fundacao de Amparo a Pesquisa do Est. Sao Paulo, Cons.

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“…sec-), and r is the luminal radius expressed in cm (Gertz, 1963;Malnic & Mello Aires, 1971;Malnic et al 1972b). Fig.…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Kinetics of luminal acidification in cortical tubules of the rat kidney.

Giebisch¹,

Malnic²,

Mello³

et al. 1977

The Journal of Physiology

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“…They were prepared for micropuncture as previously described (Malnic, de Mello Aires & Giebisch, 1972). They received a standard rat-pellet diet and were allowed free access to food and water until the time of the experiment.…”

Section: Methodsmentioning

confidence: 99%

“…In the course of such studies it was also observed that the net flux of H + into luminal phosphate corresponded to about half of that of the reabsorption rate of an equal tubular load of bicarbonate and that both acidification rates were significantly inhibited by acetazolamide (Malnic & de Mello Aires, 1971;Malnic, de Mello Aires, de Mello & Giebisch, 1972;Giebisch et al, 1977). These differences in the acidification kinetics of the two buffer species could be due either to the presence of an additional transport mechanism for ionic bicarbonate, or both processes could be mediated by hydrogen ion secretion, different rates of acidification resulting from specific properties of the two buffer systems.…”

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confidence: 99%

Role of luminal buffers in renal tubular acidification

et al. 1981

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The acidification of kinetics of artificial solutions containing buffers of different permeancy were studied in rat proximal tubules by means of stationary microperfusion techniques. Luminal pH changes were measured by antimony microelectrodes and used to calculate net rates of acidification and the approach to steady-state pH levels. For most buffer species, tracer efflux out of the lumen was compared with changes in buffer concentration as derived from calculations based on the Henderson Hasselbalch equation. Steady-state luminal pH was similar for most buffer systems studied. However, secretory hydrogen ion fluxes into the lumen were significantly higher for permeant than for less permeant buffers. The most likely explanation is that permeant buffers behave as "open" systems maintaining constant low diffusible acid levels in the lumen, whereas impermeant buffers behave as "closed" systems in which non-ionized acid levels are maintained at higher levels. A behavior consistent with this thesis was directly demonstrated for glycodiazine and, to a lesser degree, for DMO. In contrast, phosphate and creatinine behave like buffers in a "closed" system. Characteristics of proximal tubular acidification, of buffer reabsorption, and the effect thereupon of carbonic anhydrase inhibitors are satisfactorily explained by an essential role of (1) hydrogen ion secretion, (2) pK differences, and (3) different permeance of the non-ionized buffer species. However, specific transport mechanisms may, in addition, also contribute to differences in transepithelial buffer movement.

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“…Microperfusion studies in which the acidification of luminal bicarbonate and phosphate buffers was studied have characterized some of the mechanisms by which proximal and distal tubules reabsorb bicarbonate and secrete H ions (Gottschalk, Lassiter & Mylle, 1960;Malnic & Mello Aires, 1971;Malnic, Mello Aires, de Mello & Giebisch, 1972;Vieira & Malnic, 1968; Giebisch, Malnic, de Mello & de Mello-Aires, 1977). In such studies it became apparent that not only hydrogen ion secretion but also buffer anion movement per se could affect the observed pH changes.…”

Section: Introductionmentioning

confidence: 99%

Mechansims and components of renal tubular acidification.

Cassola¹,

Giebisch²,

Malnic³

1977

The Journal of Physiology

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SUMMARY1. Renal cortical tubules of control and acetazolamide infused rats were perfused with 100 mm phosphate buffer at pH 5-5. The rate of alkalinization was measured by means of antimony micro-electrodes and was used to compute passive H ion fluxes from lumen to blood across the proximal and distal tubular-epithelium.2. The importance of other ionic movements that might contribute to pH changes of luminal buffers (chloride inflow into the lumen and bicarbonate diffusion across the epithelium) was assessed but found to be minor. H ion movements accounted for the majority of the observed pH changes.3. H ion permeability of the tubular wall was calculated from the measured H fluxes and transepithelial concentration differences. It was 1-10 cm/sec, several orders of magnitude larger than those for other ions.However, such values are compatible with the mobility of protons in a medium of structured water within the limiting membrane.4. A kinetic analysis of the mechanism of movement of H ions across the renal tubule is presented on the basis of experiments in which acidification and alkalinization of luminal buffers was followed in stationary microperfusions. The data are compatible with a pump-leak system in the proximal tubule, and with a model with low H ion permeability and a gradient dependent pump in the distal tubule.

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Acidification of phosphate buffer in cortical tubules of rat kidney

Cited by 12 publications

References 3 publications

Kinetics of luminal acidification in cortical tubules of the rat kidney.

Kinetics of luminal acidification in cortical tubules of the rat kidney.

Role of luminal buffers in renal tubular acidification

Mechansims and components of renal tubular acidification.

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