Regulation Of Acid-base Balance Research Articles

Genetic ablation of Rhbg in the mouse does not impair renal ammonium excretion

NH(4)(+) transport by the distal nephron and NH(4)(+) detoxification by the liver are critical for achieving regulation of acid-base balance and to avoid hyperammonemic hepatic encephalopathy, respectively. Therefore, it has been proposed that rhesus type B glycoprotein (Rhbg), a member of the Mep/Amt/Rh NH(3) channel superfamily, may be involved in some forms of distal tubular acidosis and congenital hyperammonemia. We have tested this hypothesis by inactivating the RHbg gene in the mouse by insertional mutagenesis. Histochemical studies analyses confirmed that RHbg knockout (KO) mice did not express Rhbg protein. Under basal conditions, the KO mice did not exhibit encephalopathy and survived well. They did not exhibit hallmarks of distal tubular acidosis because neither acid-base status, serum potassium concentration, nor bone mineral density was altered by RHbg disruption. They did not have hyperammonemia or disturbed hepatic NH(3) metabolism. Moreover, the KO mice adapted to a chronic acid-loading challenge by increasing urinary NH(4)(+) excretion as well as their wild-type controls. Finally, transepithelial NH(3) diffusive permeability, or NH(3) and NH(4)(+) entry across the basolateral membrane of cortical collecting duct cells, measured by in vitro microperfusion of collecting duct from KO and wild-type mice, was identical with no apparent effect of the absence of Rhbg protein. We conclude that Rhbg is not a critical determinant of NH(4)(+) excretion by the kidney and of NH(4)(+) detoxification by the liver in vivo.

Carbonic Anhydrase Inhibitors. Design of Fluorescent Sulfonamides as Probes of Tumor-Associated Carbonic Anhydrase IX That Inhibit Isozyme IX-Mediated Acidification of Hypoxic Tumors

Sulfonamides inhibit the catalytic activity of carbonic anhydrases (CAs, EC 4.2.1.1), enzymes participating in the regulation of acid-base balance and ion transport in many tissues. Carbonic anhydrase IX (CA IX), a transmembrane isoform with predominant association with tumors and limited distribution in normal tissues, is strongly overexpressed by hypoxia. Hypoxia increases the catalytic performance of CA IX contributing to microenvironmental acidosis, which influences cancer progression and treatment outcome. CA IX represents a target for detection and therapy of hypoxic tumors. Sulfonamide CA IX selective inhibitors accumulate only in hypoxic cells containing CA IX, reversing acidification mediated by this enzyme. The design of fluorescent sulfonamides that preferentially inhibit the activity of CA IX, showing reduced penetration through the plasma membranes and binding to hypoxic cells expressing CA IX, is reported here. These inhibitors represent promising candidates for developing anticancer therapies based on tumor-associated CA isozyme inhibition and offer interesting tools for imaging and further investigation of hypoxic tumors.

Pronephric regulation of acid-base balance; Coexpression of carbonic anhydrase type 2 and sodium-bicarbonate cotransporter-1 in the late distal segment

The kidney plays a critical role in regulating the composition of the blood, including pH. The major buffer regulating pH of the blood is bicarbonate. Bicarbonate is freely filtered through the glomerulus and must be recovered from the primary filtrate to maintain appropriate buffering capacity and blood pH. In this report, the expression of carbonic anhydrase type 2 within the late distal segment of pronephroi is described. This expression precisely overlaps that of the sodium-bicarbonate transporter XNBC1. In mammalian kidneys, these two proteins collaborate in the transepithelial recovery of bicarbonate from the kidney filtrate. Coexpression of the genes encoding these proteins in Xenopus embryos indicates that pronephroi use the same recovery system and that this system is largely localized to the late portion of the pronephric distal segment. Not only do the simple pronephroi regulate water and solute balance, they also appear to regulate blood pH in a manner akin to that of the vastly more complex mammalian metanephric kidneys.

Two classic papers in acid-base physiology: contributions of R. F. Pitts, R. S. Alexander, and W. D. Lotspeich.

This essay looks at the historical significance of two APS classic papers that are freely available online: Pitts RF and Alexander RS. The nature of the renal tubular mechanism for acidifying the urine. Am J Physiol 144: 239-254, 1945 (http://ajplegacy.physiology.org/cgi/reprint/144/2/239). Pitts RF and Lotspeich WD. Bicarbonate and the renal regulation of acid base balance. Am J Physiol 147: 138-154, 1946 (http://ajplegacy.physiology.org/cgi/reprint/147/1/138).

Intranephron localization and regulation of the V1a vasopressin receptor during chronic metabolic acidosis and dehydration in rats.

The intrarenal localization and role of the V1a vasopressin receptor in body fluid homeostasis are unclear. We investigated the intranephron localization of V1a receptor mRNA and protein using reverse transcription (RT)-competitive polymerase chain reaction (PCR) and immunohistochemistry with a specific polyclonal antibody. To determine whether the V1a receptor is involved in the regulation of acid-base balance, we also examined the effects of acute and chronic metabolic acidosis and dehydration on V1a receptor expression. V1a mRNA was expressed most abundantly in the cortical collecting ducts (CCD) and decreased in the deeper CD. Expression in the glomeruli and thick ascending limbs was low. The immunohistochemical study revealed the presence of the V1a receptor in the glomeruli, the thick ascending limbs and the CD. Dehydration decreased V1a mRNA expression in the CD. Chronic metabolic acidosis increased V1a receptor mRNA expression in the CD but decreased V2 receptor mRNA expression. Western blot analysis revealed up-regulation of the V1a receptor protein in chronic metabolic acidosis. Incubation of microdissected CCD or outer medullary CD (OMCD) in a low-pH (or or low-HCO3-) medium increased the levels of V1a receptor mRNA but decreased V2 receptor mRNA expression. Incubating OMCD with arginine vasopressin (AVP) and the V1a receptor antagonist (OPC21268) increased V2 receptor mRNA expression compared with incubation with AVP alone. These data suggest that V1a receptors are present primarily in the principal and intercalated cells in the CD and that these receptors are involved in the regulation of water and acid-base balance.

Regulation by Glucocorticoids of Expression and Activity of rBSC1, the Na+-K+(NH4+)-2Cl−Cotransporter of Medullary Thick Ascending Limb

To assess whether glucocorticoids regulate rBSC1, the apical Na(+)-K(+)(NH(4)(+))-2Cl(-) cotransporter of kidney medullary thick ascending limb (MTAL), studies were performed in normal rats, adrenalectomized (ADX) rats, and ADX rats infused with dexamethasone for 6 days. The effects of dexamethasone on rBSC1 were also studied in vitro using isolated rat MTAL segments. Cotransport activity was estimated by intracellular pH measurements; rBSC1 protein was quantified in MTAL crude membranes by immunoblotting analysis, and mRNA was quantified by quantitative reverse transcription-polymerase chain reaction. The abundance of rBSC1 protein and mRNA increased in ADX rats infused with dexamethasone compared with ADX rats (p < 0. 04). In addition, application of dexamethasone for 1-3 h to MTALs caused rBSC1 protein and mRNA abundance and cotransport activity to significantly increase in a hyperosmotic medium (450 mosmol/kg of H(2)O) containing 0.7 nm arginine vasopressin, which is an in vitro experimental condition that resembles the in vivo MTAL environment. Results obtained in various media and with 8-bromo-cAMP indicated that stimulation of rBSC1 expression by glucocorticoids required interactions between glucocorticoid receptor- and cAMP-dependent factors. Up to 100 nm d-aldosterone had no effect on cotransport activity in vitro. Thus glucocorticoids directly stimulate MTAL rBSC1 expression and activity, which contributes to glucocorticoid-dependent effects on the renal regulation of acid-base balance and urinary concentrating ability.

Defective fluid and HCO(3)(-) absorption in proximal tubule of neuronal nitric oxide synthase-knockout mice.

Using renal clearance techniques and in situ microperfusion of proximal tubules, we examined the effects of N(G)-monomethyl-L-arginine methyl ester (L-NAME) on fluid and HCO(3)(-) transport in wild-type mice and also investigated proximal tubule transport in neuronal nitric oxide synthase (nNOS)-knockout mice. In wild-type mice, administration of L-NAME (3 mg/kg bolus iv) significantly increased mean blood pressure, urine volume, and urinary Na(+) excretion. L-NAME, given by intravenous bolus and added to the luminal perfusion solution, decreased absorption of fluid (60%) and HCO(3)(-) (49%) in the proximal tubule. In nNOS-knockout mice, the urinary excretion of HCO(3)(-) was significantly higher than in the wild-type mice (3.12 +/- 0.52 vs. 1. 40 +/- 0.33 mM) and the rates of HCO(3)(-) and fluid absorption were 62 and 72% lower, respectively. Both arterial blood HCO(3)(-) concentration (20.7 vs. 25.7 mM) and blood pH (7.27 vs. 7.34) were lower, indicating a significant metabolic acidosis in nNOS-knockout mice. Blood pressure was lower in nNOS-knockout mice (76.2 +/- 4.6 mmHg) than in wild-type control animals (102.9 +/- 8.4 mmHg); however, it increased in response to L-NAME (125.5 +/- 5.07 mmHg). Plasma Na(+) and K(+) were not significantly different from control values. Our data show that a large component of HCO(3)(-) and fluid absorption in the proximal tubule is controlled by nNOS. Mice without this isozyme are defective in absorption of fluid and HCO(3)(-) in the proximal tubule and develop metabolic acidosis, suggesting that nNOS plays an important role in the regulation of acid-base balance.

Ig-Hepta, a Novel Member of the G Protein-coupled Hepta-helical Receptor (GPCR) Family That Has Immunoglobulin-like Repeats in a Long N-terminal Extracellular Domain and Defines a New Subfamily of GPCRs

A novel member of the G protein-coupled receptor (GPCR) family was cloned and characterized, which is unique, among the members, in its long extracellular domain comprising Ig-like repeats and in its high expression predominantly in the lung. The clone (Ig-Hepta) was first identified as a polymerase chain reaction product generated with primers designed to amplify secretin receptor family members including the parathyroid hormone-related peptide receptors. Analysis of the open reading frame of cDNAs isolated from a rat lung cDNA library indicated that Ig-Hepta is a protein of 1389 amino acid residues and has two Ig-like repeats in the N-terminal extracellular domain (exodomain) of 1053 amino acid residues and 7 transmembrane spans in the C-terminal region. Northern blot analysis revealed very high expression of its mRNA in the lung and low but detectable levels in the kidney and heart. The mRNA expression in the lung was found to be strongly induced postnatally. Biochemical analysis indicated that Ig-Hepta is a highly glycosylated protein and exists as a disulfide-linked dimer. Immunohistochemistry on rat lung and kidney sections revealed dense localization of Ig-Hepta in alveolar walls and intercalated cells in the collecting duct, respectively, suggesting a role in the regulation of acid-base balance. Ig-Hepta defines a new subfamily of GPCRs.

Renal Carbonic Anhydrase Activity in DBA/2FG-pcy/pcy Mice with Inherited Polycystic Kidney Disease.

DBA/2FG-pcy/pcy (D2-pcy) mice are a hereditary murine model of slowly progressive polycystic kidney disease (PKD) and characterized by the persistent excretion of acidic urine, in association with polyuria, after weaning. In this study, the activity of carbonic anhydrase (CA) and it histological distribution in the kidney of D2-pcy mice were investigated by immunohistochemistry. Significantly higher CA activity was detected in the cytosolic, but not membrane, fraction of kidney homogenates in 5-week-old D2-pcy mice than in age-matched, control DBA/2 (D2) mice, and a more rapid rate of urine acidification was noted in 11-week-old mice when acetazolamide, an inhibitor of the enzyme, was administered orally. By immunohistochemistry for the major renal CA isoenzyme (CA II), epithelial cells in the distal straight tubules and the cortical collecting ducts were stained intensely, whereas those of the proximal convoluted tubules had only weak and diffuse staining. The glomeruli, the proximal straight tubules and the ascending thin limb of Henle's loop were almost free from staining. In the cells lining cysts and/or dilated tubules, CA II activity was well preserved, although the staining intensity was considerably reduced in fully-flattened, lining cells of cysts, but no difference was found between D2-pcy and D2 mice in any segmental localization of renal CA II activity. From these results it seems that D2-pcy mice in the early stages of the cystic disease continue to secrete excess protons through the CA-mediated reaction that is stimulated for regulation of acid-base balance in the distal portion of the nephron and the collecting duct in kidney. It also suggests that monitoring urine pH may be useful in predicting the effects of early interventions on the progression of slowly developing renal cysts.

RENAL REGULATION OF ACID-BASE BALANCE

This article reviews the role of the kidneys in the regulation of acid-base balance. It is intended as a guide for those who teach this aspect of renal physiology to health professions students. An approach is described, which begins with an overview of acid-base balance and then proceeds to describe the details of renal H1 transport and the important role the production and excretion of NH 4 plays in the ability of the kidneys to generate new HCO 3 . In the overview, the role of the kidneys in acid-base balance is placed in context for the student by examining the impact of diet and cellular metabolism on acid-base balance. Also, the interactions between the kidneys and lungs to maintain extracellular HCO 3 concentration within a narrow range are described. This is followed by a detailed look at the cellular mechanisms of H1 secretion along the nephron, how these mechanisms are regulated, and how they result in the reabsorption of the filtered load of HCO 3 . Finally, the important role of NH 4 production and excretion in the generation of new HCO 3 is reviewed and highlighted.

Faecal microflora and urease activity during the first six months of infancy.

Gastrointestinal degradation of urea might, according to a new hypothesis, have consequences for the regulation of acid-base balance as well as control of breathing during infancy. Thirteen infants were investigated from their first few days of life to the age of 6 months by collecting faecal samples at the age of 3 days, 2, 3, and 6 months, respectively. The faecal microflora was determined after aerobic and anaerobic cultivation and the faecal urease activity was assessed after 36 h aerobic and anaerobic preincubation. The infants were mostly breast fed and had a faecal microflora containing anaerobic bacteria such as Bifidobacteria, Bacterioides and Lactobacilli but also aerobics such as Escherichia coli, Enterococci and sometimes Klebsiella. The faecal pH increased from approximately 5.30 to 5.90, the pH after anaerobic preincubation being on an average 0.2 pH units lower than after aerobic preincubation. Simultaneously the nitric oxide production of the faecal specimens increased approximately 10-fold and the urease activity decreased by a factor of 3 to 5. We also found an inhibitory action of nitrate, nitrite (in mumolar concentration) and nitric oxide (in parts per million concentration) on the faecal urease activity. Hence, the present results warrant further research in order to determine more precisely the action of different concentrations of various nitrous oxides on individual bacterial species, and furthermore, to assay the faecal urease activity in victims of sudden infant death syndrome as well as in infants dead due to other causes.

Involvement of renal kallikrein in the regulation of bicarbonate excretion in rats.

1. The experiments reported here were performed to test the hypothesis that renal kallikrein is involved in the regulation of acid-base balance. 2. The bicarbonate concentration and the kallikrein activity in the spontaneously voided urine of conscious rats (experiment 1) were inversely correlated (correlation coefficient (r) = -0.63, P < 0.0001). The correlation was even greater when the urinary bicarbonate concentration was expressed per milligram excreted creatinine (r = -0.74, P < 0.00002). 3. Intravenous injection of the kallikrein inhibitor aprotinin in barbiturate-anaesthetized rats (experiment 2) reduced urinary kallikrein activity (P < 0.05) and increased bicarbonate excretion rate (P < 0.012). 4. Renal arterial infusion of aprotinin in barbiturate-anaesthetized rats (experiment 3) reduced urinary kallikrein activity (120 min, P < 0.01), and increased bicarbonate excretion rate (120 min, P < 0.01). Animals infused with the inhibitor developed a moderate metabolic acidosis (base excess: control, 2.9 +/- 0.7 mM (mean +/- S.E.M.); experimental, -8.1 +/- 0.7 mM; P < 0.05). 5. The bicarbonate concentration of urine fractions obtained after retrograde injection of kallikrein through the ureter into the collecting duct system of barbiturate-anaesthetized rats was lower than that from kidneys administered the vehicle (experiment 4; P < 0.001). A retrograde injection of bradykinin was without effect (experiment 5). 6. We conclude that renal kallikrein is involved in the regulation of urinary bicarbonate excretion. Increased intraluminal activity of the enzyme reduces, and decreased kallikrein activity increases, bicarbonate excretion. The enzyme may be a component of a negative feedback loop controlling the hydrogen ion activity of the extracellular space.

In situ hybridization of H-K-ATPase beta-subunit mRNA in rat and rabbit kidney.

Through a variety of techniques, several investigators have demonstrated the presence of an H-K-adenosinetriphosphatase (H-K-ATPase) enzyme in the renal collecting duct, suggesting that this enzyme serves an important physiological role in the regulation of acid-base balance and potassium excretion by the kidney. The present study was designed to localize cells expressing H-K-ATPase beta-subunit mRNA in rat and rabbit kidney by nonradioactive in situ hybridization. A 570-bp DNA fragment of rabbit renal H-K-ATPase beta-subunit was used to produce digoxigenin-labeled riboprobes by in vitro transcription. Northern blot hybridization demonstrated transcripts in rat gastric oxyntic mucosa and kidney. In situ hybridization on kidney tissue sections demonstrated H-K-ATPase beta-subunit mRNA localization in epithelial cells, including intercalated cells in the connecting segment and cortical and medullary collecting duct, principal cells in the inner stripe of the outer medullary collecting duct, and inner medullary collecting duct cells in both the rat and the rabbit. These observations provide evidence that H-K-ATPase beta-subunit mRNA is present throughout the collecting duct of the kidney. The distribution of this message is consistent with a role for H-K-ATPase in bicarbonate absorption in both the outer and inner medullary collecting duct.

Polarized targeting of V-ATPase in kidney epithelial cells.

The membrane-associated V-ATPase that plays an important role in the regulation of acid-base balance by the kidney is a multisubunit enzyme that is densely packed into specialized membrane domains in intercalated cells. Intercalated cells can be separated into at least two subtypes, A-cells and B-cells, based on their morphological features, the distribution of V-ATPase, and the presence or absence of a basolateral chloride/bicarbonate anion exchanger (AE1) exclusively in B-cells. A-cells secrete protons into the tubule lumen, whereas B-cells secrete bicarbonate. The relative amounts of V-ATPase and AE1 in the plasma membranes of A- and B-cells are modulated under different acid-base conditions and provide a sensitive means by which urinary acidification can be controlled. The mechanisms governing the movement of acid-base transporting proteins between intracellular vesicles and the plasma membrane are under investigation. The microtubular apparatus of the cell is involved in maintaining both apical and basolateral polarity of the enzyme, and different isoforms of V-ATPase subunits may also be involved in the selective targeting of V-ATPase to different membrane domains.

The Kidney: Physiology and Pathophysiology

Volume 1 A history of renal physiology in 1950, Carl W. Gottschalk: general principles of electrolyte regulation - organization and control of body fluid compartments, molecular biology of transport organization of the kidney - structural organization, functional organization. Volume 2 Organization of the kidney - renal regulation of extrarenal function water and electrolyte exchanges - renal regulation of water balance - normal, renal regulation of water balance - deranged, renal regulation of sodium and chloride - normal, renal regulation of sodium and chloride - deranged, renal regulation of potassium - normal, renal regulation of potassium - deranged, renal regulation of magnesium - normal, renal regulation of magnesium - deranged, renal regulation of calcium - normal, renal regulation of calcium - deranged, renal regulation of phosphate - normal, renal regulation of phosphate - deranged, renal regulation of acid-base balance - normal, renal regulation of acid-base balance - deranged. Volume 3: Water and electrolyte exchanges - renal regulation of organic solutes and trace metals - normal, renal regulation of organic solutes and trace metals - deranged, renal regulation of proteins and macromolecules - normal, renal regulation of proteins and macromolecules - normal, renal regulation of proteins and macromolecules - deranged, extrinsic and intrinsic renal failure - failure of renal function, renal pharmacology.

The roles of intracellular buffers and bone mineral in the regulation of acid-base balance in mammals

1. 1. Regulation of intracellular and extracellular pH may conflict in their requirements for movement of acid or base. 2. 2. Cells make a positive or a negative contribution to ‘tissue buffering’ of extracellular fluid (ECF), depending on their internal buffer value, on the tightness of their internal pH control by membrane mechanisms, and on the nature of the acid-base disturbance. 3. 3. A role is suggested for electrogenic NaHC03 co-transport in some of the ion shifts that occur in acid-base disturbances. 4. 4. The time course of ‘tissue buffering’ in nephrectomized mammals in hypercapnia is variable, and it is far from clear in intact, unanaesthetized mammals. 5. 5. Buffering of ECF by Ca salts of bone mineral in acidosis can only be substantial if accompanied by Ca excretion; the release of HCO 3 with Na and K is more significant. 6. 6. The relative importance of cells and of bone mineral in the buffering of ECF is unclear.

Interaction of Respiration, Ion Regulation, and Acid-Base Balance in the Everyday Life of Aquatic Crustaceans

Extracellular and intracellular acid-base balance is necessary for the maintenance of normal metabolic processes. The primary source of acid is metabolically produced CO2, and the CO2/HCO3− system is the most significant buffer. The regulation of acid-base balance is complex, involving the interaction between respiratory gas exchange and ion transport. In aquatic crustaceans respiration is governed by the need to extract oxygen from water, an O2-poor medium; thus, acid-base balance is maintained primarily through ion transport mechanisms. These mechanisms include Na+/H+ and Cl−/HCO3− exchange processes that are sensitive to the extracellular acid-base status of the animal. In marine crabs, ion regulation and acid-base balance are accomplished by the posterior gills, while in freshwater species all gills and the antennal gland perform these functions. Intracellular acid-base balance appears to be maintained primarily by ion transport across the cell membrane. Hemolymph pH varies inversely with acclimation temperature and salinity. In both cases Pco2 remains nearly constant, and the pH change is a result of changes in hemolymph HCO3− concentrations brought about by ion exchange mechanisms. Environmental hypercapnia or hyperoxia induces a repiratory acidosis characterized by increased Pco2, low pH, and elevated HCO3−; this is partially compensated for by ion exchange processes that bring about a further increase in hemolymph HCO3−. Exercise causes a mixed respiratory and metabolic acidosis with compensation via H+ ion excretion and hyperventilation.

Decrease in ureagenesis by partial hepatectomy does not influence acid-base balance

It has been suggested that urea synthesis participates directly in body pH homeostasis by removal of bicarbonate. To elucidate this hypothesis sodium bicarbonate or sodium chloride was infused (11.5 mumol/min) for 90 min into control rats and into rats that had undergone an 85% hepatectomy immediately before starting the infusion. Urea synthesis rate was 2.6 +/- 0.3 mumol/min (mean +/- SE) in controls, and was significantly (P less than 0.01) reduced to 1.0 +/- 0.2 mumol/min in partially hepatectomized rats. At the start of bicarbonate infusion, pH was 7.38 and 7.34 in control and partially hepatectomized rats, respectively, and at the end of infusion, pH was 7.56 and 7.51. Standard bicarbonate at start of bicarbonate infusion was 21.9 and 21.3 mM in controls and partially hepatectomized, respectively, and it increased to 32.7 and 29.9 mM at end of infusion. In saline-infused rats a slight decrease of approximately 0.05 pH units was observed during the experiment, but again no difference emerged between control and partially hepatectomized rats. It is concluded that a major role of the liver in the regulation of acid-base balance is unlikely.

The Regulation of Acid-Base Balance

The Regulation of Acid-Base Balance

The Regulation of Acid-Base Balance

The Regulation of Acid-Base Balance