Activity Of HCO3 Research Articles

Efficient degradation of refractory organics for carbonate-containing wastewater via generation carbonate radical based on a photoelectrocatalytic TNA-MCF system

Carbonate widely exist in wastewater and natural water. Here we proposed an efficient refractory organics degradation method for carbonate-containing wastewater via generating carbonate radical based on a photoelectrocatalytic TNA-MCF system. In the system, TiO2 nanotube arrays (TNA) and modified carbon felt (MCF) were used as photoanode and cathode, respectively. HCO3− was used as electrolyte. The results show that the system achieved 85.78% removal rate after 120 min in rhodamine B degradation, which is 30% higher than that using SO42− as electrolyte. The excellent performance is attributed to the strong oxidation of CO3− to organics, which originates from the reactions between HCO3− and hvb+ on TNA photoanode. It was also generated from the activation of HCO3− with H2O2 or O2− on MCF cathode. Moreover, the mechanism of CO3− formation and its efficient degradation of organics were investigated. These results demonstrate that this system has a potential application in refractory organics degradation.

Changes to Intestinal Transport Physiology and Carbonate Production at Various CO2 Levels in a Marine Teleost, the Gulf Toadfish (Opsanus beta).

Most marine teleosts defend blood pH during high CO2 exposure by sustaining elevated levels of HCO3(-) in body fluids. In contrast to the gill, where measures are taken to achieve net base retention, elevated CO2 leads to base loss in the intestine of marine teleosts studied to date. This loss is thought to occur through transport pathways previously demonstrated to be involved with routine osmoregulation in marine teleosts. The main objective of this study was to characterize the intestinal transport physiology of the gulf toadfish (Opsanus beta) when exposed to varied levels of CO2: control, 5,000, 10,000, and 20,000 μatm CO2 (0.04, 0.5, 1, and 2 kPa, respectively). Results of this study suggest that intestinal apical anion exchange is highly responsive to hypercarbia, evidenced by a dose-dependent increase in intestinal luminal HCO3(-) (mmol L(-1)) that was mirrored by a reduction in Cl(-) (mmol L(-1)). Despite activation of HCO3(-) transport pathways typically used during osmoregulation, fractional fluid absorption was only significantly lower at the highest level of CO2. Although increased HCO3(-) excretion could provide more substrate for intestinally produced carbonates, carbonate production was not significantly increased during hypercarbia at the levels tested. This study is among the first to thoroughly characterize how compensation for elevated CO2 affects transport physiology and carbonate production in the marine fish intestine. This deeper understanding may be particularly relevant when considering the impacts of future predicted ocean acidification, where prolonged base loss may alter the energetic cost of acid-base balance or osmoregulation in marine fish.

Essential role of carbonic anhydrase XII in secretory gland fluid and HCO3 (-) secretion revealed by disease causing human mutation.

Fluid and HCO3 (-) secretion is essential for all epithelia; aberrant secretion is associated with several diseases. Carbonic anhydrase XII (CA12) is the key carbonic anhydrase in epithelial fluid and HCO3 (-) secretion and works by activating the ductal Cl(-) -HCO3 (-) exchanger AE2. Delivery of CA12 to salivary glands increases salivation in mice and of the human mutation CA12(E143K) markedly inhibits it. The human mutation CA12(E143K) causes disease due to aberrant CA12 glycosylation, and misfolding resulting in loss of AE2 activity. Aberrant epithelial fluid and HCO3 (-) secretion is associated with many diseases. The activity of HCO3 (-) transporters depends of HCO3 (-) availability that is determined by carbonic anhydrases (CAs). Which CAs are essential for epithelial function is unknown. CA12 stands out since the CA12(E143K) mutation causes salt wasting in sweat and dehydration in humans. Here, we report that expression of CA12 and of CA12(E143K) in mice salivary glands respectively increased and prominently inhibited ductal fluid secretion and salivation in vivo. CA12 markedly increases the activity and is the major HCO3 (-) supplier of ductal Cl(-) -HCO3 (-) exchanger AE2, but not of NBCe1-B. The E143K mutation alters CA12 glycosylation at N28 and N80, resulting in retention of the basolateral CA12 in the ER. Knockdown of AE2 and of CA12 inhibited pancreatic and salivary gland ductal AE2 activity and fluid secretion. Accordingly, patients homozygous for the CA12(E143K) mutation have a dry mouth, dry tongue phenotype. These findings reveal an unsuspected prominent role of CA12 in epithelial function, explain the disease and call for caution in the use of CA12 inhibitors in cancer treatment.

Acclimation to hypercarbia protects cardiac contractility and alters tissue carbohydrate metabolism in the Amazonian armored catfish Pterygoplichthys pardalis

The armored catfish Pterygoplichthys pardalis tolerates environmental hypercarbia, high partial pressures of CO2 (\(P_{{{\text{CO}}_{ 2} }}\)), by preferentially protecting intracellular pH (pHi) in the face of extracellular acidosis. This response is associated with ionic changes which may disrupt contractility in cardiac muscle, and it is not known whether acclimation to hypercarbia provides protection against these changes. We studied the influence of different \(P_{{{\text{CO}}_{ 2} }}\) acclimation histories on cardiac muscle function using isometrically contracting ventricular strip preparations. Fish were held for >4 months at 21 mmHg \(P_{{{\text{CO}}_{ 2} }}\) and then exposed to normocarbia (6 mmHg \(P_{{{\text{CO}}_{ 2} }}\)) for either 15 h or 5–6 days. Acclimation to chronic hypercarbia eliminated the negative inotropic effects of in vitro hypercarbia, decreased extracellular Ca2+ sensitivity, and reduced maximum pacing frequency in ventricular strip preparations. Fish acclimated to chronic hypercarbia also exhibited hepatic glycogen and plasma glucose accumulation, and lower plasma lactate levels compared to fish acclimated to normocarbia for 5–6 days. We suggest chronic hypercarbia may induce cardiac remodeling to protect contractility and reduce the energetic demands of pHi regulation. The activation of HCO3− synthesis pathways may decrease glucose utilization and enhance carbohydrate stores, potentially providing protection against hypoxia, a stressor frequently encountered in conjunction with hypercarbia in the Amazon.

Activation of ciliary beating by a mucolytic agent, ambroxol, in bronchioles of mice

Ambroxol has been used as a mucolytic agent in pulmonary diseases. In this study, we studied the effects of ambroxol on ciliary beat frequency (CBF) and ciliary bend amplitude (CBA) of the bronchioles. Mice were anestetized by pentobarbital sodium (70mg/kg, ip) and bronchiolar ciliary cells were isolated from lungs by an elastase treatment. In a HCO3−‐containing solution, ambroxol increased CBA and CBF in a concentration dependent manner: ambroxol (10μM) increased CBA and CBF by 30 % within 15 min. However, in a HCO3−‐free solution, it did not induce any increase in CBA and CBF, although the switch from the HCO3−‐containing solution to the HCO3−‐free solution increased them. Measurement of intracellular pH (pHi) demonstrated that ambroxol (10 μM) increased pHi gradually in bronchiolar ciliary cells. These suggest that an increase in pHi induced by ambroxol increases CBA and CBF. To confirm the effects of pHi on CBA and CBF, an NH4+ pulse was applied. An increase in pHi increased CBA and CBF, whereas a decrease in pHi decreased them. Diisothiocyanostilbene‐disulfonic acid (DIDS) abolished the increases in CBA and CBF induced by ambroxol. In bronchiolar ciliary cells, ambroxol increases pHi via activation of HCO3−/Cl− exchanges, which increases CBA and CBF.

Characterisation of CO2 and HCO3- Uptake during Steady-state Photosynthesis in the Cyanobacterium Synechococcus PCC7942 Steady-state Photosynthesis in the Cyanobacterium Synechococcus PCC7942

We have recently developed a mass spectrometric disequilibrium technique to measure CO2 and HCO3- uptake during steady-state photosynthesis in cyanobacteria and microalgae (Badger et al. 1993). Using this technique, we have found differences between the characteristics of Ci uptake in Synechococcus PCC7942 under steady- and non-steady state photosynthesis. Both low- and high-Ci cells have the capacity to transport CO2 and HCO3-. In contrast to reported results obtained under non-steady-state conditions, the activity of HCO3- uptake is higher than that of CO2 uptake, even in high-Ci cells. Dramatic increases in the affinity of the CI transport system for CO2 and HCO3- but not in maximal transport activities were found when high-Ci cells were induced under low-Ci conditions. These changes in affinity occurred within about 4 h. The affinity for HCO3- but not CO2 also increased when uptake activities were measured at a lower pH (pH 7.5 compared to pH 8.5), especially in high-Ci cells. HCO3- uptake was also more sensitive to LiCl inhibition than CO2 uptake. LiCl inhibition was partially relieved in the presence of NaCI. The carbonic anhydrase inhibitor ethoxyzolamide inhibited both CO2 and HCO3- uptake to about the same extent, consistent with the view that both transports might share a common 'carbonic anhydrase-like' component. The results are discussed in relation to previous results obtained under non-steady-state conditions.

Na(+)-HCO3- symport in the sheep cardiac Purkinje fibre.

1. Intracellular pH (pHi) was recorded in isolated sheep cardiac Purkinje fibres using liquid sensor ion-selective microelectrodes in conjunction with conventional (3 M-KCl) microelectrodes (to record membrane potential). 2. In HEPES-buffered solution (pH0 7.4), pHi recovery from an intracellular acid load (20 mM-NH4Cl removal) was blocked by 1 mM-amiloride, consistent with the inhibition of Na(+)-H+ exchange. Replacement of the HEPES buffer with CO2-HCO3- caused a transient acidosis followed by an amiloride-resistant recovery of pHi to more alkaline levels (n = 43). This implies the presence of a HCO3(-)-dependent pHi regulatory mechanism. 3. Comparison of the membrane potential with the equilibrium potential for HCO3- ions (EHCO3) estimated during amiloride-resistant pHi recovery, showed that for polarized fibres (membrane potential Em approximately -80 mV), there was a net outward electrochemical driving force for HCO3- ions. Hence the amiloride-resistant pHi recovery cannot be explained in terms of passive HCO3- influx through membrane channels. 4. Removal of external Na+ (Na0+ replaced by N-methyl-D-glucamine) inhibited HCO3(-)-dependent pHi recovery, whereas removal of external Cl- (leading to depletion of internal Cl-; Cl0- replaced by glucuronate) or short-term removal of extracellular K+ had no inhibitory effect. We suggest that a Na(+)-HCO3- co-influx causes the recovery. Replacement of external Na+ with Li+ greatly reduced HCO3(-)-dependent pHi recovery indicating that Li0+ cannot readily substitute for Na0+ on the co-transport. 5. The stilbene drug DIDS (4,4-diisothiocyano-stilbene-disulphonic acid, 500 microM) slowed HCO3(-)-dependent pHi recovery. 6. Depolarization of the membrane potential in high K0+ (44.5 mM) solution or with 5 mM-BaCl2 had no effect upon the rate of HCO3(-)-sensitive pHi recovery. This observation, when coupled with the fact that activation of HCO3(-)-dependent pHi recovery was associated with no consistent change of membrane potential, suggests that the Na(+)-HCO3- co-influx is electroneutral and voltage insensitive. 7. HCO3(-)-dependent pHi recovery was unaffected by the Na(+)-K(+)-2Cl- co-transport inhibitor, bumetanide (150 microM). 8. The contribution of Na(+)-H+ exchange and Na(+)-HCO3- co-transport to net acid efflux was assessed. At a pHi of 6.6, we estimate that the co-transport should account for 20% of total acid equivalent efflux.(ABSTRACT TRUNCATED AT 400 WORDS)

Mutational analysis of carbamyl phosphate synthetase. Substitution of Glu841 leads to loss of functional coupling between the two catalytic domains of the synthetase subunit

The synthetase subunit of Escherichia coli carbamyl phosphate synthetase has two catalytic nucleotide-binding domains, one involved in the activation of HCO3- and the second in phosphorylation of carbamate. Here we show that a Glu841----Lys841 substitution in a putative ATP-binding domain located in the carboxyl half of the synthetase abolishes overall synthesis of carbamyl phosphate with either glutamine or NH3 as the nitrogen source. Measurements of partial activities indicate that while HCO3(-)-dependent ATP hydrolysis at saturating concentrations of substrate proceeds at higher than normal rates, ATP synthesis from ADP and carbamyl phosphate is nearly completely suppressed by the mutation. These results indicate Glu841 to be an essential residue for the phosphorylation of carbamate in the terminal step of the catalytic mechanism. The Lys841 substitution also affects the kinetic properties of the HCO3- activation site. Both kcat and Km for ATP increase 10-fold, while Km for HCO3- is increased 100-fold. Significantly, NH3 decreases rather than stimulates Pi release from ATP in the HCO3(-)-dependent ATPase reaction. The increase in kcat of the HCO3(-)-dependent ATPase reaction, and an impaired ability of the Lys841 enzyme to catalyze the reaction of NH3 with carboxy phosphate, strongly argues for interactions between the two catalytic ATP sites that couple the formation of enzyme-bound carbamate with its phosphorylation.

Cloning and characterization of the genes required for inorganic carbon transport of Synechocystis PCC6803

Transformation of the high CO2-requiring mutants of Synechocystis PCC6803 defective in inorganic carbon (Ci) transport (RKa and RKb) by wild type (WT) DNA libraries restored their ability to grow under air levels of CO2. Two clones (PK-1 and HP-1), which complement RKa and RKb, respectively, were isolated from the libraries. PK-1 contained an 11.8-kilobase pair (kbp) DNA insert. The sequence of amino acid coded in the DNA in the region of the mutation showed an extensive homology to that of the ndh2 gene product of liverwort chloroplasts, which is suspected to be the subunit 2 of NADH dehydrogenase. Based on the result, we designated the gene mutated in RKa as ndh2. Inactivation of the ndh2 gene in the WT cells by inserting an aminoglycoside-3′-phosphotransferase gene generated a mutant (M57) that was unable to grow under low CO2 conditions. HP-1 contained a 5.4-kbp DNA insert. Sequencing of nucleotides in the region of the mutation revealed an open reading frame that codes a hydrophobic protein that consists of 80 amino acids. Insertional inactivation of this putative Ci transport gene, designated ictA, generated a high CO2-requiring mutant (M9). All these mutants (RKa, RKb, M9, and M57) showed very low activity of CO2 uptake into the intracellular Ci pools. The activity of HCO3− uptake was negligibly low in RKb, M9, M57 and high CO2-grown cells of RKa, and was about 10% the activity of wild type cells in low CO2-adapted cells of RKa. Key words: CO2-concentrating mechanism, inorganic carbon transport, Synechocystis PCC6803, mutant, NADH dehydrogenase, insertional inactivation.

Evidence for mitochondrial origin of the HCO3(-)-ATPase in brush border membranes of rat proximal tubules.

High HCO3(-)-ATPase activity is known to exist in mitochondria of renal tubular cells. In brush border membrane (BBM) preparations of proximal tubules such an anion-stimulated enzyme was also found. However, these preparations always contained mitochondrial markers. The putative localization and the role of this ATPase in BBM is still controversial. Some authors consider the HCO3(-)-ATPase in the BBM to be a mitochondrial contamination; others attribute to this ATPase a key role in H+ transport in the proximal tubule. To reinvestigate this problem, BBMs from rat kidney cortex were isolated by a simple, rapid (1.5-h) Ca2+-precipitation method, yielding a BBM fraction enriched 12.4-fold with respect to the marker enzyme leucine aminopeptidase (LAP). There was no basolateral Na+-K+-ATPase and no mitochondrial succinate dehydrogenase detectable. Cytochrome c oxidase was drastically reduced to 7 +/- 1% of that observed in the homogenate (TH). The activity of HCO3(-)-ATPase in the BBM fraction was 19 +/- 4 IU/g protein, i.e., 27% that of the homogenate. As sonication of the TH exclusively increases the activity of HCO3(-)-ATPase, its relative activity was 7.5% and thus equal to that of the mitochondrial marker. In many BBM preparations no HCO3(-)-ATPase was detectable. In those BBM preparations in which traces of HCO3(-)-ATPase were found, this activity coincided with that of cytochrome c oxidase in the respective preparation. There was a constant activity ratio of cytochrome c oxidase/HCO3(-)-ATPase in the TH, BBM, and pellet 1. The activity of HCO3(-)-ATPase in BBM did not depend on the activity of LAP.(ABSTRACT TRUNCATED AT 250 WORDS)