Distal tubule unidirectional HCO3 reabsorption in vivo during acute and chronic metabolic alkalosis in the rat

1994 ◽  
Vol 266 (6) ◽  
pp. F919-F925 ◽  
Author(s):  
D. Z. Levine ◽  
M. Iacovitti ◽  
S. Buckman ◽  
D. Vandorpe ◽  
V. Harrison ◽  
...  
Keyword(s):  
Metabolic Alkalosis ◽  
Distal Tubule ◽  
Bicarbonate Secretion ◽  
Bafilomycin A1 ◽  
Secretory Phase ◽  
Plasma Bicarbonate ◽  
Bicarbonate Reabsorption ◽  
Chloride Depletion ◽  
Distal Tubules

During metabolic alkalosis (MA) associated with 2 days of dietary chloride restriction, there is net bicarbonate secretion by rat distal tubules in vivo, whereas after 5 wk of chloride depletion alkalosis there is net bicarbonate reabsorption. To examine unidirectional components of net bicarbonate reabsorption during chronic MA, we measured distal tubule unidirectional bicarbonate secretion (Jsec) and reabsorption (Jreab), as well as the inhibitor sensitivity of Jreab. In control, 2-day, and 7-day alkalosis, Jsec was similar. Jreab, however, was only present in 7-day MA (17 +/- 3 pmol.min-1.mm-1, P < 0.05). This Jreab was completely suppressed by perfusion with 10(-7) M bafilomycin A1, partially suppressed with 10(-5) M Schering (Sch)-28080 (4 +/- 2 pmol.min-1.mm-1, P < 0.1), and converted into a secretory flux by 3 mM amiloride. We conclude that adaptation to chloride depletion MA from the acute secretory phase to the chronic state, where plasma bicarbonate is sustained at elevated levels, does not involve suppression of distal tubule Jsec but rather enhanced Jreab, which is sensitive to bafilomycin, Sch-28080, and amiloride.

In vivo adaptation of bicarbonate reabsorption by rat distal tubules during acid loading

1994 ◽  
Vol 267 (5) ◽  
pp. F737-F747 ◽  
Author(s):  
D. Z. Levine ◽  
M. Iacovitti ◽  
S. Buckman ◽  
D. Vandorpe ◽  
V. Harrison ◽  
...  
Keyword(s):  
Water Flux ◽  
Distal Tubule ◽  
Bafilomycin A1 ◽  
Bicarbonate Reabsorption ◽  
Distal Tubules ◽  
Acid Loading ◽  
Fasted Rats ◽  
Predominant Effect ◽  
Stimulation Of

We carried out in vivo microperfusion experiments in acid-loaded rats to characterize the adaptive response of the unidirectional components secretory flux (Jsec) and reabsorptive flux (Jreab)] of distal tubule bicarbonate reabsorption and to test the hypothesis that Jreab is dependent on bafilomycin A1-sensitive H(+)-adenosinetriphosphatase activity. During 18 h of severe acidosis there was a significant decrease in Jsec (-15 +/- 3 vs. -38 +/- 5 pmol.min-1.mm-1, P < 0.05) and a significant increase in Jreab (37 +/- 6 vs. 0 +/- 5 pmol.min-1.mm-1, P < 0.05), which was insensitive to 10(-5) M bafilomycin A1, 10(-5) M Sch-28080, and 3 mM amiloride. After 3 days of acid loading, these same inhibitors reduced Jreab by approximately 60%. However, when water flux was completely inhibited by isosmotic perfusion, a significant Jreab (15 +/- 2 pmol.min-1.mm-1) resistant to 10(-5) M bafilomycin A1 persisted, as in severe acidosis. In reabsorbing distal tubules of overnight-fasted rats, Sch-28080 elicited no inhibition, whereas bafilomycin A1 and amiloride had significant effects (28 +/- 5, 24 +/- 4, respectively, vs. 50 +/- 4 pmol.min-1.mm-1 for fasted rats, P < 0.05). Thus, although Jsec is reduced in the transition from mild to severe metabolic acidosis of 18-h duration, the predominant effect is a stimulation of bafilomycin A1-resistant Jreab.

Distal tubule bicarbonate reabsorption during rebound metabolic alkalosis

1991 ◽  
Vol 69 (11) ◽  
pp. 1784-1788 ◽  
Author(s):  
David H. Vandorpe ◽  
Steven P. Nadler ◽  
David Z. Levine
Keyword(s):  
Metabolic Acidosis ◽  
Metabolic Alkalosis ◽  
Distal Tubule ◽  
Bicarbonate Transport ◽  
Bicarbonate Concentration ◽  
Plasma Bicarbonate ◽  
Bicarbonate Reabsorption ◽  
Collecting Ducts ◽  
Persistent Elevation

Rebound metabolic alkalosis is a transient alkalemia that is seen during recovery from NH4Cl-induced metabolic acidosis. The persistent elevation of plasma bicarbonate concentration is the result of continuing excretion of net acid by the kidney. Bicarbonate transport by inner medullary collecting ducts has been reported by others to proceed normally (i.e., bicarbonate reabsorption continues in this segment) during rebound metabolic alkalosis. No other segmental responses have been evaluated. Since the surface distal tubule of the rat is known to both reabsorb and secrete bicarbonate in vivo, it was of interest to determine the response of this segment. Our results show that the distal tubule microperfused in vivo during rebound metabolic alkalosis continues to reabsorb significant amounts of bicarbonate, despite the presence of systemic alkalemia that we have previously shown to be associated with distal tubule bicarbonate secretion.Key words: rebound metabolic alkalosis, distal tubule, micropuncture, bicarbonate reabsorption.

Mechanism of acidification along cortical distal tubule of the rat

1994 ◽  
Vol 266 (2) ◽  
pp. F218-F226 ◽  
Author(s):  
R. Fernandez ◽  
M. J. Lopes ◽  
R. F. de Lira ◽  
W. F. Dantas ◽  
E. J. Cragoe Junior ◽  
...  
Keyword(s):  
Channel Blocker ◽  
Exchange Resin ◽  
Rat Kidney ◽  
Specific Inhibitor ◽  
Distal Tubule ◽  
Ringer Solution ◽  
Na Channel ◽  
Bafilomycin A1 ◽  
Bicarbonate Reabsorption ◽  
Distal Tubules

The cellular mechanism of luminal acidification (bicarbonate reabsorption) was studied in cortical distal tubules of rat kidney. The stopped-flow microperfusion technique was applied to early distal (ED) and late distal (LD) segments, perfused with bicarbonate Ringer solution to which specific inhibitors were added, to measure bicarbonate reabsorption [HCO3 flux (JHCO3)]. pH and transepithelial potential difference (Vt) were recorded by double-barreled H+ exchange resin/reference (1 M KCl) electrodes. Amiloride increased stationary pH and reduced Vt in both early and late segments. Hexamethylene-amiloride (HMA), a specific Na(+)-H+ exchange blocker, reduced JHCO3 in both segments (ED by 43.6 and LD by 40.3%) without affecting Vt. Benzamil, an Na(+)-channel blocker, reduced Vt by 75.9 in ED and 74.9% in LD but had no significant effect on acidification in both segments. The specific inhibitor of H(+)-ATPase, bafilomycin A1, inhibited LD JHCO3 at a concentration of 2 x 10(-7) M by 49%, but ED was inhibited by 24% only at 2 x 10(-6) M. Sch-28080, an inhibitor of gastric H(+)-K(+)-ATPase, reduced JHCO3 by 35% in LD of K(+)-depleted rats but not in control rats and had no effect on ED. These data indicate that, in ED, bicarbonate reabsorption is mediated mostly by Na(+)-H+ exchange. In LD, there is evidence for contribution of Na(+)-H+ exchange, vacuolar H(+)-ATPase, and H(+)-K(+)-ATPase (in K(+)-depleted rats) to bicarbonate reabsorption.

Determination of disequilibrium pH in the rat kidney in vivo: evidence of hydrogen secretion

1981 ◽  
Vol 240 (2) ◽  
pp. F138-F146 ◽  
Author(s):  
T. D. DuBose ◽  
L. R. Pucacco ◽  
N. W. Carter
Keyword(s):  
Carbonic Anhydrase ◽  
Metabolic Alkalosis ◽  
Rat Kidney ◽  
Respiratory Acidosis ◽  
Distal Tubule ◽  
Distal Nephron ◽  
Bicarbonate Reabsorption ◽  
Disequilibrium Ph ◽  
Tubule Fluid

The recent demonstration of elevated PCO2 in structures of the rat renal cortex indicated that previous determinations of disequilibrium pH (pHDq), and thus the differentiation of H+ secretion from bicarbonate reabsorption per se, required further evaluation. A new aspiration pH electrode was developed to allow tubule fluid to achieve chemical equilibrium at the PCO2 prevailing in vivo. In control and bicarbonate-loaded rats a pHDq was not observed in either proximal or distal tubules. After intravenous benzolamide a significant acid pHDq was observed in the proximal (but not the distal) nephron, and increased further during metabolic alkalosis. During combined metabolic alkalosis and respiratory acidosis a significant pHDq was present in the distal but not in the proximal tubule. Aldosterone administration to bicarbonate-loaded, hypercapnic rats did not alter the distal pHDq further. When present, the pHDq in the distal tubule was obliterated by carbonic anhydrase infusion. We conclude that proximal but not distal tubule fluid is in functional contact with carbonic anhydrase; the enzyme is in excess in the proximal lumen and H2CO3 did not accumulate even during conditions associated with increased H+ secretion; the basal rate of H+ secretion in the distal nephron accessible to cortical micropuncture is less than previously assumed. The data support the view that H+ secretion is the major mechanism of renal bicarbonate reabsorption.

Control of bicarbonate transport in collecting tubules from normal and remnant kidneys

1989 ◽  
Vol 256 (4) ◽  
pp. F680-F687 ◽  
Author(s):  
L. L. Hamm ◽  
K. S. Hering-Smith ◽  
V. M. Vehaskari
Keyword(s):  
Renal Mass ◽  
Distal Tubule ◽  
Bicarbonate Transport ◽  
Bicarbonate Secretion ◽  
Bicarbonate Reabsorption ◽  
Collecting Tubule ◽  
Collecting Tubules ◽  
Acid Loading

Bicarbonate transport in the rabbit cortical collecting tubule (CCT) and outer medullary collecting tubule (MCT) in vitro was studied under two types of conditions that were anticipated to alter distal tubule bicarbonate transport: 1) reduction of renal mass, and 2) acid and base loading in vivo. Bicarbonate secretion (both total and acetazolamide sensitive) and bicarbonate reabsorption (studied separately) in CCT and bicarbonate reabsorption in the MCT were not different between tubules from normal and remnant kidneys. The control or conditioning of the separate processes of bicarbonate secretion and bicarbonate reabsorption was also studied in CCT from normal and remnant kidneys. Bicarbonate secretion was not increased by base-loading animals with either normal or remnant kidneys. In contrast, bicarbonate secretion was consistently decreased by acid loading (studied in CCT from remnant kidneys). Bicarbonate reabsorption in the CCT was not altered by acid or base loads given to animals with normal kidneys. And bicarbonate reabsorption in MCT was not increased by acid loading of animals with remnant kidneys. These studies demonstrate that bicarbonate transport (and its conditioning by acid or base loads in vivo) in both CCT and MCT in vitro is not altered by reduction of renal mass in rabbits. The predominant conditioning effect of acid or base loads in vivo is for acid loads to inhibit CCT bicarbonate secretion.

Augmented bidirectional HCO3 transport by rat distal tubules in chronic alkalosis

1991 ◽  
Vol 261 (2) ◽  
pp. F308-F317 ◽  
Author(s):  
D. E. Wesson ◽  
G. M. Dolson
Keyword(s):  
Metabolic Alkalosis ◽  
Distal Tubule ◽  
Free Flow ◽  
Proton Secretion ◽  
Nephron Segment ◽  
Distal Tubules ◽  
And Control

Free-flow micropuncture studies show both augmented net HCO3 reabsorption in the distal tubule of rats with chronic metabolic alkalosis and higher HCO3 delivery to this nephron segment. The present studies in rats used in vivo microperfusion of surface distal tubules to investigate whether the augmented net reabsorption 1) was due to decreased HCO3 secretion and/or to increased proton secretion or 2) depended on the higher HCO3 delivery to the distal tubule. Artificial perfusates were designed to simulate in situ deliveries of HCO3 to the distal tubules of both alkalotic and control animals and to represent extremes of in situ Cl deliveries. Rather than being decreased, both measured and calculated HCO3 secretion were higher in the alkalotic animals for each perfusate used. Similarly, calculated proton secretion (difference between net HCO3 reabsorption and calculated HCO3 secretion) was higher for the alkalotic animals using each HCO3-containing perfusate. Augmented net HCO3 reabsorption by alkalotic animals was more clearly demonstrated using higher HCO3 deliveries and Cl-free perfusates. These studies demonstrate that both the reabsorptive and secretory components of net HCO3 transport are increased in the distal tubule of animals with chronic metabolic alkalosis.

Reduced bicarbonate secretion mediates increased distal tubule acidification induced by dietary acid

1996 ◽  
Vol 271 (3) ◽  
pp. F670-F678 ◽  
Author(s):  
D. E. Wesson
Keyword(s):  
Distal Tubule ◽  
Bicarbonate Secretion ◽  
Anesthetized Rats ◽  
Nephron Segment ◽  
Dietary Acid ◽  
Distal Tubules ◽  
Tubule Fluid

We examined the components of net HCO3 reabsorption (H+/HCO3 secretion) in in vivo perfused distal tubules of anesthetized rats to determine the mechanisms by which dietary acid increases acidification in this nephron segment. Animals eating a minimum electrolyte diet drank either 80 mM NH4Cl or 40 mM (NH4)2SO4 for 7-10 days and were compared with controls drinking distilled H2O. Net HCO3 reabsorption in distal tubules perfused with HCO3 concentration ([HCO3]) similar to that in situ (5 mM) was higher in (NH4)2SO4 animals than in control (21.6 +/- 1.8 vs. 12.5 +/- 1.3 pmol.mm-1.min-1, respectively, P < 0.02), but that for NH4Cl (17.9 +/- 1.5 pmol.mm-1.min-1, P = 0.09 vs. control) animals was not. Calculated H+ secretion was not different among groups perfused with the 5 mM HCO3 solution, but calculated HCO3 secretion was lower in (NH4)2SO4 animals than control (-2.4 +/- 0.3 vs. -5.3 +/- 0.6 pmol.mm-1.min-1, respectively, P < 0.02), but that for NH4Cl (-7.2 +/- 0.7 pmol.mm-1.min-1, P = not significant vs. control) was not. When distal tubules were perfused with solutions containing higher [HCO3] (10 nM), both net HCO3 reabsorption and calculated H+ secretion were significantly higher than control in both acid-ingesting groups. The data show that reduced HCO3 secretion mediates the increased distal tubule acidification induced by dietary acid, particularly at the low tubule fluid [HCO3] in situ. The data also show that acid ingested as the Cl- compared with the SO4(-) salt does not reduce HCO3 secretion and less effectively increases acidification in this nephron segment.

Depressed distal tubule acidification corrects chloride-deplete alkalosis in rats

1990 ◽  
Vol 259 (4) ◽  
pp. F636-F644 ◽  
Author(s):  
D. E. Wesson
Keyword(s):  
Linear Regression ◽  
Proximal Tubule ◽  
Metabolic Alkalosis ◽  
Wistar Rats ◽  
Distal Tubule ◽  
Bicarbonate Reabsorption ◽  
Dependent Relationship ◽  
Distal Tubules ◽  
Lower Slope ◽  
Filtered Load

We investigated the relative contributions made by the proximal and distal tubule to the correction of Cl-deplete metabolic alkalosis induced by systemic administration of NaCl. Free-flow micropuncture was used to examine net bicarbonate reabsorption in superficial proximal and distal tubules of anesthetized Munich-Wistar rats during maintenance and correction of chronic furosemide-induced Cl-deplete metabolic alkalosis. The distal tubule of animals with correcting vs. maintained alkalosis had a lower fractional reabsorption of bicarbonate (38 vs. 75%, P less than 0.001) and a lower slope of the linear regression comparing absorption to delivered load (0.48 vs. 0.99, P less than 0.02). By contrast, proximal tubule of animals with correcting vs. maintained alkalosis had fractional reabsorption (85 vs. 90%, P = 0.07) and slopes of the regression comparing reabsorption to filtered load (1.09 vs. 0.98, P = 0.48) that were not different. The data indicate that correction of Cl-deplete metabolic alkalosis induced by NaCl administration involves a qualitative decreased in bicarbonate reabsorption in distal tubule with maintenance of the same load-dependent relationship for bicarbonate reabsorption in proximal tubule.

Maximal proton secretory rate of rat distal tubules is higher during chronic metabolic alkalosis

1991 ◽  
Vol 261 (5) ◽  
pp. F753-F759
Author(s):  
D. E. Wesson ◽  
G. M. Dolson
Keyword(s):  
Metabolic Alkalosis ◽  
Distal Tubule ◽  
Substrate Affinity ◽  
Free Solution ◽  
Secretory Rate ◽  
Proton Secretion ◽  
Distal Tubules ◽  
The Difference ◽  
And Control

In vivo microperfusion studies show augmented proton secretion in the distal tubule of rats with chronic metabolic alkalosis. The present studies used the same technique to determine whether this augmented proton secretion is due predominantly to an increase in substrate affinity or alternatively to a predominant increase in the maximal proton secretory rate. Surface distal tubules of alkalotic and control rats were microperfused in vivo with solutions containing increasing concentrations of HCO3. Proton secretion was determined as the difference between measured net HCO3 reabsorption and passive HCO3 transport calculated by use of the permeability derived from perfusing with a HCO3-free solution. Proton secretion was expressed as a function of the initial luminal HCO3 concentration and was assumed to follow saturable Michaelis-Menten kinetics. Alkalotic animals had a significantly higher Km (33.9 vs. 21.6 mM, P less than 0.03) and Vmax (223.8 vs. 99.1 pmol.mm-1.min-1, P less than 0.001) compared with control. These data are consistent with the augmented proton secretion in the distal tubule of alkalotic animals as predominantly due to an increased maximal proton secretory rate rather than to increased substrate affinity.

Application of the disequilibrium pH method to investigate the mechanism of urinary acidification

1983 ◽  
Vol 245 (5) ◽  
pp. F535-F544
Author(s):  
T. D. DuBose
Keyword(s):  
Metabolic Alkalosis ◽  
Collecting Duct ◽  
Respiratory Acidosis ◽  
Distal Tubule ◽  
Bicarbonate Reabsorption ◽  
Urinary Acidification ◽  
Technological Advances ◽  
Papillary Collecting Duct ◽  
Disequilibrium Ph

DuBose, Thomas D., Jr. Application of the disequilibrium pH method to investigate the mechanism of urinary acidification. Am. J. Physiol. 245 (Renal Fluid Electrolyte Physiol. 14): F535-F544, 1983.--The cellular mechanism of renal bicarbonate reabsorption has been debated for four decades. Recent technological advances have allowed distinction between primary bicarbonate reabsorption and a proton secretory mechanism. The disequilibrium pH method has been applied widely for this purpose and has supported the latter hypothesis uniformly. The demonstration of elevated values for PCO2 in tubular and vascular structures of the renal cortex has not altered this view. Indeed, by employing a newly developed method for measurement of equilibrium pH in vivo that permits contact with the environment within the tubule lumen to continue, we demonstrated an acid disequilibrium pH in the proximal tubule after carbonic anhydrase inhibition equal to -0.68 pH units. A spontaneous disequilibrium pH was not present in the distal tubule during control conditions or during metabolic alkalosis but was demonstrated during combined respiratory acidosis-metabolic alkalosis. This finding agrees qualitatively with observed rates of bicarbonate reabsorption in the perfused distal tubule in vivo. With use of similar techniques, an acid disequilibrium pH in conjunction with elevated values for PCO2 was observed in the papillary collecting duct. Thus, proton secretion appears to be the predominant mechanism of bicarbonate reabsorption in superficial nephrons and explains, as well, the means by which the urine-to-blood PCO2 gradient in alkaline urine is established.

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