H+ ion secretion in proximal tubule of low-CO2/HCO 3 − perfused isolated rat kidney

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.

Section: Effect Of Co2 After Carbonic Anhydrase Inhibitionmentioning

confidence: 99%

Section: Effect Of Co2 After Carbonic Anhydrase Inhibitionmentioning

confidence: 99%

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

Amorena¹,

Fernandes²,

Malnic³

1984

“…Acidification and alkalinization half-times are a function of R1, Rs and C. Because the buffer load is imposed by the experimental conditions (luminal phosphate buffer content), C is constant. The conductive H-ion flux through Rs seems to be only a small part of passive backflux of H ion (Rubio et al 1982;Amorena et al 1984).…”

Section: Discussionmentioning

confidence: 99%

“…The rate of this alkalinization has been used as a measure of H-ion efflux from the tubular lumen. Although it has been shown that above pH 6 only a minor component of this 91 A. G. LOPES, G. MALNIC AND N. A. REBOUqAS efflux rate is electrodiffusive (Rubio, De Mello, Mangili & Malnic, 1982), this flux should be increased when an additional mechanism of H-ion transfer, in this case a protonophore (DNP), is introduced into the system. Fig.…”

Section: Methodsmentioning

confidence: 99%

Dinitrophenol effect on proximal tubular acidification in the rat.

Lopes¹,

Malnic²,

Rebouças³

1985

SUMMARY1. The effect of 10-3 M-dinitrophenol (DNP) on renal tubular acidification was studied in proximal tubules of rat kidneys perfused with mammalian Ringer solution. Alkaline (pH 7 8) or acid (pH 5 8) phosphate-buffered solutions were injected into the lumen, and pH changes recorded with antimony micro-electrodes.2. Luminal perfusion with DNP caused complex acidification or alkalinization curves, an initial rapid shift toward a higher than control pH being followed by a slower acidification. Acidification half-times of the initial phase (th = 1-6 s) were markedly shorter than controls (6-2 s).3. This response was probably due to transient action of DNP, since keeping constant peritubular DNP levels by capillary perfusion caused simple exponential pH curves. In such experiments luminal pH increased from pH 6-6-6-8 to 7-1-7-2, while acidification and alkalinization ti decreased from about 7 s to 3-5 s. Secretory H-ion fluxes increased transiently and then fell below controls after a few minutes of perfusion, while H-ion efflux from the lumen increased progressively.4. These data suggest that, besides its known effect on cell metabolism, DNP acts directly on proximal tubular cell membranes, increasing the rate of passive H-ion equilibration, both mechanisms impairing the tubular capacity to maintain normal proximal pH gradients and fluxes.

“…This effect was independent of filtered load, since it was observed during pump perfusion of proximal tubules. It is interesting to note, however, that in the isolated perfused rat kidney preparation, proximal tubule acidification is maintained to a considerable extent, leading to transepithelial pH gradients near those of normal kidney (lumen pH of 6 8) when perfusion is performed with artificial solutions which do not contain haemoglobin, and even at the Po2 of air, that is, at an oxygen supply which is markedly lower than that found in the 'in vivo' kidney (Rubio, de Mello, Mangili & Malnic, 1982). This is consistent with the well-known observation that RBF exceeds the nutritional needs of the organ.…”

Section: Introductionmentioning

confidence: 99%

Urinary and proximal tubule acidification during reduction of renal blood flow in the rat.

Jaramillo-Juárez

Aires

Malnic

1990

SUMMARY1. The effects of reduction in renal blood flow (RBF) on urinary acidification and proximal tubule H+ ion secretion were studied after partial aortic clamping in rats.2. Acute reduction of the renal perfusion pressure (from 109 + 3-88 to 77-4 + 1-05 mmHg) decreased both inulin and PAH (p-aminohippurate) clearances to about one-third of their control values. Absolute levels of urinary sodium excretion also decreased markedly, but fractional sodium excretion did not change significantly.3. Urine pH and bicarbonate levels were not affected, but titratable acidity increased significantly from 0-12 + 0-011 to 0f25 + 0-042 ,tequiv min-' ml-' glomerular filtration rate (GFR). During aortic clamping, cortical Pco2 as determined by means of Severinghaus microelectrodes was reduced by a mean value of 7 0 + 1-5 mmHg.4. Proximal tubule acidification kinetics were studied by stationary microperfusion techniques in which the time course of pH changes was monitored by pH microelectrodes. Steady-state pH fell from a mean control value of 6-77+0-03 to 6-65 + 0-02, and stationary bicarbonate concentrations from 4-70 + 0-27 to 2-84 + 0-18 mm. Acidification half-time decreased from 5-07 + 0-30 to 4-39 + 019 s, and net bicarbonate reabsorption increased from 1-63 + 0-14 to 1-99 + 0-12 nmol cm-2 S-, these changes being statistically significant.5. The experiments demonstrate that both overall acid excretion and proximal acid secretion are not compromised by a large decrease of RBF to about one-third of the control value; titratable acid excretion and proximal net bicarbonate reabsorption were even moderately increased under these conditions.