Branchial membrane-associated carbonic anhydrase activity maintains CO2 excretion in severely anemic dogfish

2004 ◽  
Vol 286 (6) ◽  
pp. R1138-R1148 ◽  
Author(s):  
K. M. Gilmour ◽  
S. F. Perry
Keyword(s):  
Carbonic Anhydrase ◽  
Teleost Fish ◽  
Carbonic Anhydrase Activity ◽  
Cell Number ◽  
Apparent Lack ◽  
Diffusion Limited ◽  
Functional Context ◽  
Branchial Membrane ◽  
Co2 Excretion

Plasma CO2 reactions in Pacific spiny dogfish ( Squalus acanthias) have access to plasma and gill membrane-associated carbonic anhydrase (CA). Acute severe experimental anemia and selective CA inhibitors were used to investigate the role of extracellular CA in CO2 excretion. Anemia was induced by blood withdrawal coupled to volume replacement with saline. Lowering hematocrit from 14.2 ± 0.4% (mean ± SE; N = 31) to 5.2 ± 0.1% ( N = 31) had no significant impact on arterial or venous CO2 tensions (PaCO2 and PvCO2, respectively) over the subsequent 2 h. Pco2 was maintained despite the reduction in red cell number and a significant 32% increase in cardiac output (V̇b), both of which have been found to cause PaCO2 increases in teleost fish. By contrast, treatment of anemic dogfish with the CA inhibitors benzolamide (1.3 mg/kg) or F3500 (50 mg/kg), to selectively inhibit extracellular CA, elicited rapid and significant increases in PaCO2 of 0.68 ± 0.17 Torr ( N = 6) and 0.53 ± 0.11 Torr ( N = 7), respectively, by 30 min after treatment. These findings provide a functional context in which extracellular CA in dogfish contributes substantially to CO2 excretion. Additionally, the apparent lack of effect of V̇b changes on Pco2 suggests that, in contrast to teleost fish, CO2 excretion in dogfish does not behave as a diffusion-limited system.

scholarly journals The Periplasmic α-Carbonic Anhydrase Activity of Helicobacter pylori Is Essential for Acid Acclimation

2005 ◽  
Vol 187 (2) ◽  
pp. 729-738 ◽  
Author(s):  
Elizabeth A. Marcus ◽  
Amiel P. Moshfegh ◽  
George Sachs ◽  
David R. Scott
Keyword(s):  
Helicobacter Pylori ◽  
Membrane Potential ◽  
Carbonic Anhydrase ◽  
Membrane Integrity ◽  
Carbonic Anhydrase Activity ◽  
Knockout Mutant ◽  
Inner Membrane ◽  
Acid Acclimation

ABSTRACT The role of the periplasmic α-carbonic anhydrase (α-CA) (HP1186) in acid acclimation of Helicobacter pylori was investigated. Urease and urea influx through UreI have been shown to be essential for gastric colonization and for acid survival in vitro. Intrabacterial urease generation of NH3 has a major role in regulation of periplasmic pH and inner membrane potential under acidic conditions, allowing adequate bioenergetics for survival and growth. Since α-CA catalyzes the conversion of CO2 to HCO3 −, the role of CO2 in periplasmic buffering was studied using an α-CA deletion mutant and the CA inhibitor acetazolamide. Western analysis confirmed that α-CA was bound to the inner membrane. Immunoblots and PCR confirmed the absence of the enzyme and the gene in the α-CA knockout. In the mutant or in the presence of acetazolamide, there was an ∼3 log10 decrease in acid survival. In acid, absence of α-CA activity decreased membrane integrity, as observed using membrane-permeant and -impermeant fluorescent DNA dyes. The increase in membrane potential and cytoplasmic buffering following urea addition to wild-type organisms in acid was absent in the α-CA knockout mutant and in the presence of acetazolamide, although UreI and urease remained fully functional. At low pH, the elevation of cytoplasmic and periplasmic pH with urea was abolished in the absence of α-CA activity. Hence, buffering of the periplasm to a pH consistent with viability depends not only on NH3 efflux from the cytoplasm but also on the conversion of CO2, produced by urease, to HCO3 − by the periplasmic α-CA.

Role of enzymes in the mechanism of shell penetration by the muricid gastropod, Thais lapillus (L.)

1977 ◽  
Vol 55 (11) ◽  
pp. 1846-1857 ◽  
Author(s):  
Roy S. Webb ◽  
A. S. M. Saleuddin
Keyword(s):  
Acid Phosphatase ◽  
Carbonic Anhydrase ◽  
Phosphatase Activity ◽  
Acid Phosphatase Activity ◽  
Carbonic Anhydrase Activity ◽  
Marker Enzyme ◽  
Biochemical Activity ◽  
Significant Difference ◽  
Muricid Gastropods

The role of the boring organ in the mechanism of shell penetration by Thais lapillus (L.), a muricid gastropod, has been investigated by cytochemistry and biochemistry. Sites of acid phosphatase and carbonic anhydrase activity were localized and the biochemical activities of these enzymes were measured in the boring organ of both nonboring and actively boring animals. The lysosomal marker enzyme, acid phosphatase, was investigated to assess the role of lysosomes in the boring mechanism. Acid phosphatase activity was localized on the microvillar membranes of the epithelial cells of the boring organ. There was no significant difference in the biochemical activity of acid phosphatase between actively boring and nonboring specimens. Carbonic anhydrase was localized prominently in the epithelium of the boring organ. The microvilli showed no localization but all other regions of the epithelium were dominated by reaction product. The boring organ demonstrated high levels of carbonic anhydrase activity but no significant difference could be detected between actively boring and nonboring specimens. The possible involvement of these enzymes and their role in the mechanism of shell penetration by muricid gastropods has been discussed.

scholarly journals THE ROLE OF PLASMA CO2 TENSION AND CARBONIC ANHYDRASE ACTIVITY IN THE RENAL REABSORPTION OF BICARBONATE*

1960 ◽  
Vol 39 (11) ◽  
pp. 1706-1721 ◽  
Author(s):  
Floyd C. Rector ◽  
Donald W. Seldin ◽  
Albert D. Roberts ◽  
Jerry S. Smith
Keyword(s):  
Carbonic Anhydrase ◽  
Carbonic Anhydrase Activity ◽  
Renal Reabsorption

Functional role of carbonic anhydrase in intestinal electrolyte transport

1986 ◽  
Vol 251 (5) ◽  
pp. G682-G687 ◽  
Author(s):  
A. N. Charney ◽  
J. D. Wagner ◽  
G. J. Birnbaum ◽  
J. N. Johnstone
Keyword(s):  
Carbonic Anhydrase ◽  
Functional Role ◽  
Carbonic Anhydrase Activity ◽  
Electrolyte Transport ◽  
Sodium Absorption ◽  
Ascending Colon ◽  
Sprague Dawley ◽  
Acid Base Balance ◽  
Descending Colon

We examined the role of carbonic anhydrase activity in intestinal transport by measuring the effect of systemic pH and PCO2 on electrolyte transport in the presence and absence of luminal acetazolamide. Adult Sprague-Dawley rats were anesthetized, and ileal and colonic segments were perfused with Ringer solution that was acetazolamide-free or that contained 0.1 mM sodium acetazolamide. Consecutive states of acute respiratory alkalosis and acidosis were created by changing the inspired CO2 from 0% (room air) to 8% CO2. In the ileum, acetazolamide perfusion did not affect the increment in net sodium and chloride absorption caused by a reduction in systemic pH. Mucosal carbonic anhydrase activity in this segment was measurable, although very low. In both the ascending and descending colon, acetazolamide perfusion reduced the increment in net sodium absorption caused by an increase in systemic PCO2. In addition, acetazolamide increased the chloride absorptive response to PCO2 in the ascending colon but did not affect the chloride response at all in the descending colon. Colonic mucosal carbonic anhydrase exhibited a proximal-to-distal gradient of activity: levels in the ascending colon were severalfold greater than in the descending colon. These findings suggest a functional role for carbonic anhydrase in mediating the colonic but not the ileal absorptive response to changes in systemic acid-base balance.

Central CO2 chemoreception in developing bullfrogs: anomalous response to acetazolamide

2003 ◽  
Vol 94 (3) ◽  
pp. 1204-1212 ◽  
Author(s):  
Barbara E. Taylor ◽  
Michael B. Harris ◽  
E. Lee Coates ◽  
Matthew J. Gdovin ◽  
J. C. Leiter
Keyword(s):  
Carbonic Anhydrase ◽  
Late Stage ◽  
Rana Catesbeiana ◽  
Early Stage ◽  
Lung Ventilation ◽  
Carbonic Anhydrase Activity ◽  
Spinal Nerve ◽  
Before And After ◽  
Hypercapnic Response

Central CO2 chemoreception and the role of carbonic anhydrase were assessed in brain stems from Rana catesbeiana tadpoles and frogs. Buccal and lung rhythms were recorded from cranial nerve VII and spinal nerve II during normocapnia and hypercapnia before and after treatment with 25 μM acetazolamide. The lung response to acetazolamide mimicked the hypercapnic response in early-stage and midstage metamorphic tadpoles and frogs. In late-stage tadpoles, acetazolamide actually inhibited hypercapnic responses. Acetazolamide and hypercapnia decreased the buccal frequency but had no effect on the buccal duty cycle. Carbonic anhydrase activity was present in the brain stem in every developmental stage. Thus more frequent lung ventilation and concomitantly less frequent buccal ventilation comprised the hypercapnic response, but the response to acetazolamide was not consistent during metamorphosis. Therefore, acetazolamide is not a useful tool for central CO2 chemoreceptor studies in this species. The reversal of the effect of acetazolamide in late-stage metamorphosis may reflect reorganization of central chemosensory processes during the final transition from aquatic to aerial respiration.

Effects of dextran-bound inhibitors on carbonic anhydrase activity in isolated rat lungs

1986 ◽  
Vol 61 (5) ◽  
pp. 1849-1856 ◽  
Author(s):  
T. A. Heming ◽  
C. Geers ◽  
G. Gros ◽  
A. Bidani ◽  
E. D. Crandall
Keyword(s):  
Molecular Weight ◽  
Carbonic Anhydrase ◽  
Time Course ◽  
Co2 Concentration ◽  
Carbonic Anhydrase Activity ◽  
Low Molecular Weight ◽  
Co2 Diffusion ◽  
Rat Lungs ◽  
Co2 Excretion ◽  
Isolated Rat

Effects of macromolecular Prontosil-dextran inhibitors (PD) on carbonic anhydrase (CA) activity in isolated rat lungs were studied. Isolated lungs were perfused with Krebs-Ringer bicarbonate (KRB) solutions containing no inhibitor, PD 100,000 (mol wt 100,000), PD 5,000 (mol wt 5,000), or low-molecular-weight inhibitors (Prontosil or acetazolamide). The time course of effluent perfusate pH equilibration was measured in a stop-flow pH electrode apparatus. Pulmonary CO2 excretion (Vco2) was monitored by continuously recording expired CO2 concentration. The lungs were ventilated with room air and perfused at 37 degrees C with KRB prebubbled with 5% CO2- 20% O2- 75% N2. The results obtained show that both the low-molecular-weight inhibitors and PD′s caused postcapillary pH disequilibria (delta pH) in effluent perfusate. However, only acetazolamide and Prontosil caused a reduction in Vco2. These results suggest that there is an intravascular CA, presumably associated with endothelial cell membranes, that is accessible to all inhibitors used and is responsible in part for equilibration of the CO2- HCO3- -H+ reactions in the perfusate but, under the conditions used, does not affect CO2 excretion; and there is an extravascular (possibly intracellular) CA that can be inhibited by low-molecular-weight inhibitors, is primarily responsible for enhanced CO2 transfer across the alveolar-capillary barrier (perhaps via facilitation of CO2 diffusion), and is in part responsible for pH equilibration.

Membrane-associated carbonic anhydrase in gills of the blue crab, Callinectes sapidus

1987 ◽  
Vol 252 (5) ◽  
pp. R966-R971 ◽  
Author(s):  
R. P. Henry
Keyword(s):  
Carbonic Anhydrase ◽  
Blue Crab ◽  
Callinectes Sapidus ◽  
Rapid Development ◽  
Respiratory Acidosis ◽  
Basal Membrane ◽  
Ion Regulation ◽  
Co2 Excretion

The presence of the enzyme carbonic anhydrase (CA) on the basal membrane of the branchial endothelial cells in the blue crab and its physiological significance were studied in vivo using a membrane-impermeant CA inhibitor, quaternary ammonium sulfanilamide (QAS). Injection of QAS into the hemolymph of Callinectes sapidus resulted in the rapid development of a respiratory acidosis; PCO2 rose almost 2 Torr, pH was lowered by approximately 0.25 units, and total CO2 rose by 2 mM. These results support the hypothesis that membrane-associated CA exposed to hemolymph is present in the crustacean gill and that it is physiologically significant in mobilizing hemolymph HCO-3 to CO2 to facilitate CO2 excretion across the gill. The recovery from this acidosis coincides with the clearance of the inhibitor from the hemolymph. Hemolymph osmotic and ionic parameters were unaffected by QAS, reconfirming the role of branchial cytoplasmic CA in ion regulation and also providing a convenient bioassay for determining CA inhibitor permeability in the intact organism.

Effect of thiazides on colonic NaCl absorption: role of carbonic anhydrase

1991 ◽  
Vol 261 (3) ◽  
pp. F452-F458 ◽  
Author(s):  
D. S. Goldfarb ◽  
A. J. Chan ◽  
D. Hernandez ◽  
A. N. Charney
Keyword(s):  
Carbonic Anhydrase ◽  
Colonic Mucosa ◽  
Distal Colon ◽  
Carbonic Anhydrase Activity ◽  
Sprague Dawley ◽  
Colonic Absorption ◽  
Nacl Absorption ◽  
Sprague Dawley Rats ◽  
Rat Distal Colon

The mechanisms by which the benzothiadiazide class of diuretics inhibit electroneutral NaCl absorption are not fully understood. We studied the mechanisms of thiazide action in perfused loops of distal colon in anesthetized male Sprague-Dawley rats. Hydroflumethiazide (1 mM) reversibly inhibited greater than 40% of Na, Cl, and water absorption. Prior exposure of the colon to the carbonic anhydrase inhibitor methazolamide (0.1 mM) prevented the effects of hydroflumethiazide and metolazone, a thiazide-like drug, on colonic absorption. In Ussing flux chambers, addition of hydroflumethiazide to both the mucosal and serosal bathing solutions (but not to the mucosal solution alone) caused marked decreases in Na and Cl absorption. Such inhibition only occurred at concentrations of hydroflumethiazide (0.1 and 1.0 mM) that inhibited greater than 90% of carbonic anhydrase activity in homogenized colonic mucosa. We conclude that an important mechanism by which thiazides inhibit NaCl absorption in the rat distal colon is by inhibition of mucosal carbonic anhydrase. In tissues containing this enzyme, this mechanism of thiazide effect on ion flux must be considered.

H + transport in urinary epithelia

1978 ◽  
Vol 235 (2) ◽  
pp. F77-F88 ◽  
Author(s):  
Q. Al-Awqati
Keyword(s):  
Carbonic Anhydrase ◽  
Metabolic Pathways ◽  
Indirect Evidence ◽  
Carbonic Anhydrase Activity ◽  
Passive Movement ◽  
Electrochemical Gradient ◽  
Subcellular Organelles ◽  
Optimal Function ◽  
New Discovery

This review of urinary acidification is primarily based on studies in isolated epithelia such as the turtle bladder. Despite the lack of unambiguous proof, the wealth of indirect evidence suggests that the cause of bicarbonate absorption is H+ secretion into the lumen. The mechanisms that regulate H+ transport are discussed. The electrochemical gradient for protons across the membrane is found to be the most fundamental regulator not only of passive movement but also of active transport. CO2 and aldosterone stimulate H+ transport, the latter by a mechanism apparently separate from the effect of this hormone on sodium transport. Although carbonic anhydrase activity is important for optimal function of the H+ pump, the results with carbonic anhydrase inhibitors need to be interpreted with caution. The evidence for Na:H exchange is reviewed and found to be not very persuasive, The metabolic pathways that fuel H+ transport are found to be all the major energy-yielding reactions in the cell, but particular prominence is given to the new discovery of the role of the pentose shunt in energizing transport. Finally, I discuss the important role H+ transport in energy transduction in subcellular organelles.

Sign in / Sign up

Export Citation Format

Share Document