Luminal disequilibrium pH and ammonia transport in outer medullary collecting duct [corrected and issued with original paging in Am J Physiol 1987 Aug;253(2 Pt 2)]

1987 ◽  
Vol 252 (6) ◽  
pp. F1148-F1157 ◽  
Author(s):  
R. A. Star ◽  
M. B. Burg ◽  
M. A. Knepper
Keyword(s):  
Carbonic Anhydrase ◽  
Collecting Duct ◽  
Carbonic Anhydrase Inhibitor ◽  
Acidic Ph ◽  
Ammonia Transport ◽  
Outer Stripe ◽  
Medullary Collecting Duct ◽  
Disequilibrium Ph ◽  
Luminal Ph ◽  
The Relationship

We measured bicarbonate, ammonia, and luminal pH in segments of the rabbit outer medullary collecting duct (OMCD) to determine the relationship between luminal pH and ammonia transport. Both the inner-stripe and outer-stripe portions of the OMCD absorbed bicarbonate at high rates. The outer stripe OMCD generated an acidic pH disequilibrium that was reversibly dissipated by exogenous luminal carbonic anhydrase. In contrast, the inner stripe OMCD did not generate a spontaneous pH disequilibrium unless perfused with the carbonic anhydrase inhibitor acetazolamide. Ammonia secretion was three times more rapid in the outer stripe OMCD than in the inner stripe OMCD. We conclude the following. 1) Both the inner-stripe and outer-stripe portions of the rabbit OMCD secrete protons at substantial rates. 2) Functional luminal carbonic anhydrase is present in the inner stripe OMCD but absent from the outer stripe OMCD. 3) Ammonia secretion occurs predominantly by NH3 diffusion in both portions. 4) The luminal pH disequilibrium, which is normally present in the outer stripe OMCD, enhances ammonia secretion.

Luminal disequilibrium pH and ammonia transport in outer medullary collecting duct

1987 ◽  
Vol 253 (2) ◽  
pp. F1148-F1157 ◽  
Author(s):  
Robert A. Star ◽  
Maurice B. Burg ◽  
Mark A. Knepper
Keyword(s):  
Carbonic Anhydrase ◽  
Carbonic Acid ◽  
Collecting Duct ◽  
Ammonium Bicarbonate ◽  
Ammonia Transport ◽  
Outer Stripe ◽  
Medullary Collecting Duct ◽  
Disequilibrium Ph ◽  
Luminal Ph ◽  
The Relationship

We measured bicarbonate, ammonia, and luminal pH in segments of the rabbit outer medullary collecting duct (OMCD) to determine the relationship between luminal pH and ammonia transport. Both the inner-stripe and outer-stripe portions of the OMCD absorbed bicarbonate at high rates. The outer stripe OMCD generated an acidic pH disequilibrium that was reversibly dissipated by exogenous luminal carbonic anhydrase. In contrast, the inner stripe OMCD did not generate a spontaneous pH disequilibrium unless perfused with the carbonic anhydrase inhibitor acetazolamide. Ammonia secretion was three times more rapid in the outer stripe OMCD than in the inner stripe OMCD. We conclude the following. 1) Both the inner-stripe and outer-stripe portions of the rabbit OMCD secrete protons at substantial rates. 2) Functional luminal carbonic anhydrase is present in the inner stripe OMCD but absent from the outer stripe OMCD. 3) Ammonia secretion occurs predominantly by NH3, diffusion in both portions. 4) The luminal pH disequilibrium, which is normally present in the outer stripe OMCD, enhances ammonia secretion. ammonia; ammonium; bicarbonate; diffusion trapping; nonionic diffusion; carbonic anhydrase; disequilibrium pH; fluorescence spectroscopy; hydrogen ion secretion; carbonic acid; acetazolamide; heterogeneity Submitted on September 15, 1986 Accepted on January 15, 1987

Distribution of luminal carbonic anhydrase activity along rat inner medullary collecting duct

1991 ◽  
Vol 260 (5) ◽  
pp. F738-F748 ◽  
Author(s):  
S. M. Wall ◽  
M. F. Flessner ◽  
M. A. Knepper
Keyword(s):  
Carbonic Anhydrase ◽  
Collecting Duct ◽  
Co2 Concentration ◽  
Carbonic Anhydrase Activity ◽  
Inner Medullary Collecting Duct ◽  
Proton Source ◽  
Total Ammonia ◽  
Medullary Collecting Duct ◽  
Disequilibrium Ph ◽  
Ammonia Flux

The isolated perfused tubule technique was utilized to determine whether endogenous luminal carbonic anhydrase is present in the initial or terminal parts of the inner medullary collecting duct (IMCD) of the rat. This was accomplished by measuring the luminal disequilibrium pH in the presence of a large luminal proton source created by perfusing the lumen with a solution containing 10 mM NH4Cl. (NH3 efflux causes H+ to be released from NH+4 in the lumen). The disequilibrium pH was calculated by subtracting the equilibrium pH from the measured pH at the end of the tubule lumen. The end-luminal equilibrium pH was calculated from the total CO2 concentration in the collected fluid, as measured by microcalorimetry. The end-luminal pH was determined by measuring the fluorescent signal from the the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF), which was added to the luminal perfusate in its nonesterified form. In the initial IMCD, there was no measurable disequilibrium pH. With the addition of the carbonic anhydrase inhibitor acetazolamide to the luminal fluid, a significant acidic pH disequilibrium was elicited. In the terminal IMCD under control conditions a statistically significant acidic disequilibrium pH was measured. The disequilibrium was obliterated when exogenous carbonic anhydrase was added to the luminal perfusate. These findings were verified by measuring total ammonia flux by ultramicrofluorometry. The results demonstrate endogenous luminal carbonic anhydrase activity in the initial IMCD but a lack of enzyme activity in the terminal IMCD.

Luminal disequilibrium pH and ammonia transport in outer medullary collecting duct

1987 ◽  
Vol 253 (1) ◽  
pp. F202-F202 ◽  
Author(s):  
Robert A. Star ◽  
Maurice B. Burg ◽  
Mark A. Knepper
Keyword(s):  
Collecting Duct ◽  
Ammonia Transport ◽  
Medullary Collecting Duct ◽  
Disequilibrium Ph ◽  
Made In

Page F1148: Robert A. Star, Maurice B. Burg, and Mark A. Knepper. “Luminal disequilibrium pH and ammonia transport in outer medullary collecting duct.” We regret that an error was made in the title of this article. The correct title and the article are reprinted in the August 1987 issue of this journal.

Luminal disequilibrium pH and ammonia transport in outer medullary collecting duct

1987 ◽  
Vol 253 (2) ◽  
pp. F376-F376
Author(s):  
Robert A. Star ◽  
Maurice B. Burg ◽  
Mark A. Knepper
Keyword(s):  
Collecting Duct ◽  
Ammonia Transport ◽  
Medullary Collecting Duct ◽  
Disequilibrium Ph ◽  
Made In

Pages F1148–F1157: Robert A. Star, Maurice B. Burg, and Mark A. Knepper. We regret that an error was made in the title of this article. The correct title and the article are reprinted here.

Disequilibrium pH and ammonia transport in isolated perfused cortical collecting ducts

1987 ◽  
Vol 253 (6) ◽  
pp. F1232-F1242 ◽  
Author(s):  
R. A. Star ◽  
I. Kurtz ◽  
R. Mejia ◽  
M. B. Burg ◽  
M. A. Knepper
Keyword(s):  
Carbonic Anhydrase ◽  
Carbonic Acid ◽  
Effective Rate Constant ◽  
Co2 Concentration ◽  
Effective Rate ◽  
Collecting Ducts ◽  
Ammonia Transport ◽  
Disequilibrium Ph ◽  
Luminal Ph ◽  
The Difference

The present study was carried out to test directly whether isolated perfused rabbit cortical collecting ducts (CCDs) spontaneously generate a luminal disequilibrium pH. We determined disequilibrium pH as the difference between 1) the actual luminal pH measured by perfusing the lumen with a membrane-impermeant pH-sensitive dye [1,4-dihydroxyphthalonitrile (1,4-DHPN)] and 2) equilibrium pH calculated from the measured total CO2 concentration in fluid collected at the end of the tubule. When the peritubular bath and perfusate had the same composition, a statistically significant acidic disequilibrium pH was found (mean -0.14 units). To determine whether the disequilibrium pH is due to an absolute lack of luminal carbonic anhydrase, we measured the effective rate constant for carbonic acid dehydration in the lumen (k-1). To do this, a lumen-to-bath NH3 concentration gradient was imposed, and the luminal pH was measured along the tubule with 1,4-DHPN. NH3 absorption caused a luminal disequilibrium pH (due to dissociation of NH+4 to NH3 and H+), whose profile along the lumen is dependent on k-1 and NH3 permeability (PNH3). PNH3 and k-1 were estimated from the luminal pH profiles using a mathematical model of proton and buffer transport. The measured k-1 (37 s-1) is within the reported range of values for uncatalyzed H2CO3 dehydration. Calculations demonstrate that the measured PNH3 (2 X 10(-3) cm/s) is high enough and the measured k-1 is low enough to explain ammonia secretion rates seen in previous studies. We conclude that proton secretion in the CCD generates an acidic luminal disequilibrium pH, associated with an absolute lack of luminal carbonic anhydrase, which enhances the net rate of NH3 secretion.

A mathematical model of rat collecting duct II. Effect of buffer delivery on urinary acidification

2002 ◽  
Vol 283 (6) ◽  
pp. F1252-F1266 ◽  
Author(s):  
Alan M. Weinstein
Keyword(s):  
Mathematical Model ◽  
Carbonic Anhydrase ◽  
Collecting Duct ◽  
Phosphate Concentration ◽  
Rate Coefficients ◽  
Urinary Flow ◽  
Urinary Acidification ◽  
Model Predictions ◽  
Disequilibrium Ph ◽  
Urinary Acid

A mathematical model of the rat collecting duct (CD) is used to examine the effect of delivered load of bicarbonate and nonbicarbonate buffer on urinary acidification. Increasing the delivered load of HCO[Formula: see text] produces bicarbonaturia, and, with luminal carbonic anhydrase absent, induces a disequilibrium luminal pH and a postequilibration increase in urinary Pco 2. At baseline flows, this disequilibrium disappears when luminal carbonic anhydrase rate coefficients reach 1% of full catalysis. The magnitude of the equilibration Pco 2 depends on the product of urinary acid phosphate concentration and the disequilibrium pH. Thus, although increasing phosphate delivery to the CD decreases the disequilibrium pH, the increase in urinary phosphate concentration yields an overall increase in postequilibration Pco 2. In simulations of experimental HCO[Formula: see text] loading in the rat, model predictions of urinary Pco 2 exceed the measured Pco 2 of bladder urine. In part, the higher model predictions for urinary Pco 2 may reflect higher urinary flow rates and lower urinary phosphate concentrations in the experimental preparations. However, when simulation of CD function during HCO[Formula: see text] loading acknowledges the high ambient renal medullary Pco 2 (5), the predicted urinary Pco 2 of the model CD is yet that much greater. This discrepancy cannot be resolved within the model but requires additional experimental data, namely, concomitant determination of urinary buffer concentrations within the tubule fluid sampled for Pco 2 and pH. This model should provide a means for simulating formal testing of urinary acidification and thus for examining hypotheses regarding transport defects underlying distal renal tubular acidosis.

Basolateral ammonium transport by the mouse inner medullary collecting duct cell (mIMCD-3)

2004 ◽  
Vol 287 (4) ◽  
pp. F628-F638 ◽  
Author(s):  
Mary E. Handlogten ◽  
Seong-Pyo Hong ◽  
Connie M. Westhoff ◽  
I. David Weiner
Keyword(s):  
Collecting Duct ◽  
Duct Cell ◽  
Ammonium Transport ◽  
Transport Activity ◽  
Acid Base ◽  
Ammonia Transport ◽  
Medullary Collecting Duct ◽  
Extracellular Sodium ◽  
Permeable Support ◽  
Exchange Activity

The renal collecting duct is the primary site for the ammonia secretion necessary for acid-base homeostasis. Recent studies have identified the presence of putative ammonia transporters in the collecting duct, but whether the collecting duct has transporter-mediated ammonia transport is unknown. The purpose of this study was to examine basolateral ammonia transport in the mouse collecting duct cell (mIMCD-3). To examine mIMCD-3 basolateral ammonia transport, we used cells grown to confluence on permeable support membranes and quantified basolateral uptake of the radiolabeled ammonia analog [14C]methylammonia ([14C]MA). mIMCD-3 cell basolateral MA transport exhibited both diffusive and transporter-mediated components. Transporter-mediated uptake exhibited a Kmfor MA of 4.6 ± 0.2 mM, exceeded diffusive uptake at MA concentrations below 7.0 ± 1.8 mM, and was competitively inhibited by ammonia with a Kiof 2.1 ± 0.6 mM. Transporter-mediated uptake was not altered by inhibitors of Na+-K+-ATPase, Na+-K+-2Cl−cotransporter, K+channels or KCC proteins, by excess potassium, by extracellular sodium or potassium removal or by varying membrane potential, suggesting the presence of a novel, electroneutral ammonia-MA transport mechanism. Increasing the outwardly directed transmembrane H+gradient increased transport activity by increasing Vmax. Finally, mIMCD-3 cells express mRNA and protein for the putative ammonia transporter Rh B-glycoprotein (RhBG), and they exhibit basolateral RhBG immunoreactivity. We conclude that mIMCD-3 cells express a basolateral electroneutral NH4+/H+exchange activity that may be mediated by RhBG.

scholarly journals Carbonic anhydrase II and IV mRNA in rabbit nephron segments: stimulation during metabolic acidosis

1998 ◽  
Vol 274 (2) ◽  
pp. F259-F267 ◽  
Author(s):  
Shuichi Tsuruoka ◽  
Ann M. Kittelberger ◽  
George J. Schwartz
Keyword(s):  
Metabolic Acidosis ◽  
Carbonic Anhydrase ◽  
Mrna Expression ◽  
Collecting Duct ◽  
Proximal Tubules ◽  
Rabbit Kidney ◽  
Rt Pcr ◽  
Chronic Metabolic Acidosis ◽  
Nephron Segments ◽  
Medullary Collecting Duct

Carbonic anhydrase (CA) facilitates renal bicarbonate reabsorption and acid excretion. Cytosolic CA II catalyzes the buffering of intracellular hydroxyl ions by CO2, whereas membrane-bound CA IV catalyzes the dehydration of carbonic acid generated from the secretion of protons. Although CA II and IV are expressed in rabbit kidney, it is not entirely clear which segments express which isoforms. It was the purpose of this study to characterize the expression of CA II and CA IV mRNAs by specific segments of the nephron using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and to determine the effect of chronic metabolic acidosis on CA expression by those segments. Individual nephron segments (usually 1–2 mm) were isolated by microdissection and subjected to RT-PCR. Amplification was performed simultaneously for CA IV, CA II, and malate dehydrogenase (MDH), a housekeeping gene. The intensities of the PCR products were quantitated by densitometry. CA IV mRNA was expressed by S1 and S2 proximal tubules and by outer medullary collecting duct from inner stripe (OMCDi) and outer stripe and initial inner medullary collecting duct (IMCDi). CA II mRNA was expressed by S1, S2, and S3 proximal tubules, thin descending limb, connecting segment (CNT), and all collecting duct segments. Acid loading induced CA IV mRNA expression in S1 and S2 proximal tubules and in OMCDi and IMCDi. CA II mRNA was induced by acidosis in all three proximal segments and nearly all distal segments beginning with CNT. No upregulation of MDH mRNA expression occurred. These adaptive increases in CA II and IV mRNAs are potentially important in the kidney’s adaptation to chronic metabolic acidosis.

scholarly journals Histochemical carbonic anhydrase in rat inner medullary collecting duct.

1992 ◽  
Vol 40 (10) ◽  
pp. 1535-1545 ◽  
Author(s):  
J G Kleinman ◽  
J L Bain ◽  
C Fritsche ◽  
D A Riley
Keyword(s):  
Carbonic Anhydrase ◽  
Collecting Duct ◽  
Light And Electron Microscopy ◽  
Cell Types ◽  
Intercalated Cells ◽  
Cell Type ◽  
Variable Intensity ◽  
Inner Medullary Collecting Duct ◽  
Majority Population ◽  
Medullary Collecting Duct

Rat inner medullary collecting duct (IMCD) secretes substantial amounts of H+. However, carbonic anhydrase (CA), a concomitant of H+ secretion, has been generally reported absent in this segment. To reexamine this problem, we investigated CA and the morphological phenotypes of cells comprising the IMCD by CA histochemistry, using a modified Hansson technique with light and electron microscopy. Throughout the medulla, tubule cells exhibit histochemical CA activity. In the initial third of the inner medulla, a small proportion have features of intercalated cells and demonstrate some degree of CA activity. However, the majority population in the early portions of the IMCD appears to consist of principal cells. These also show CA staining of widely variable intensity, both among and within cells. A third cell type, previously called "IMCD cells", appears in the middle portion of the IMCD and is the only cell type present near the papilla tip. In contrast to previous reports, these "IMCD cells" have histochemical CA staining, also of highly variable intensity. These results demonstrate that stainable carbonic anhydrase to support acidification is present throughout the rat IMCD, both in intercalated cells and in some cells clearly not of this type. Therefore, the presence of CA is not specific for the intercalated cell type and suggests that other cell types may participate in acid secretion in IMCD.

Immunolocalization of electroneutral Na-HCO3 − cotransporter in rat kidney

2000 ◽  
Vol 279 (5) ◽  
pp. F901-F909 ◽  
Author(s):  
Henrik Vorum ◽  
Tae-Hwan Kwon ◽  
Christiaan Fulton ◽  
Brian Simonsen ◽  
Inyeong Choi ◽  
...  
Keyword(s):  
Plasma Membranes ◽  
Collecting Duct ◽  
Rat Kidney ◽  
Electron Microscopic Level ◽  
Thick Ascending Limb ◽  
Intercalated Cells ◽  
Electron Microscopic ◽  
Outer Medulla ◽  
Outer Stripe ◽  
Medullary Collecting Duct

An electroneutral Na-HCO3 − cotransporter (NBCN1) was recently cloned, and Northern blot analyses indicated its expression in rat kidney. In this study, we determined the cellular and subcellular localization of NBCN1 in the rat kidney at the light and electron microscopic level. A peptide-derived antibody was raised against the COOH-terminal amino acids of NBCN1. The affinity-purified antibody specifically recognized one band, ∼180 kDa, in rat kidney membranes. Peptide- N-glycosidase F deglycosylation reduced the band to ∼140 kDa. Immunoblotting of membrane fractions from different kidney regions demonstrated strong signals in the inner stripe of the outer medulla (ISOM), weaker signals in the outer stripe of the outer medulla and inner medulla, and no labeling in cortex. Immunocytochemistry demonstrated that NBCN1 immunolabeling was exclusively observed in the basolateral domains of thick ascending limb (TAL) cells in the outer medulla (strongest in ISOM) but not in the cortex. In addition, collecting duct intercalated cells in the ISOM and in the inner medulla also exhibited NBCN1 immunolabeling. Immunoelectron microscopy demonstrated that NBCN1 labeling was confined to the basolateral plasma membranes of TAL and collecting duct type A intercalated cells. Immunolabeling controls were negative. By using 2,7-bis-carboxyethyl-5,6-caboxyfluorescein, intracellular pH transients were measured in kidney slices from ISOM and from mid-inner medulla. The results revealed DIDS-sensitive, Na- and HCO3 −-dependent net acid extrusion only in the ISOM but not in mid-inner medulla, which is consistent with the immunolocalization of NBCN1. The localization of NBCN1 in medullary TAL cells and medullary collecting duct intercalated cells suggests that NBCN1 may be important for electroneutral basolateral HCO3 − transport in these cells.

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