Carbon dioxide transport and carbonic anhydrase in blood and muscle

Diverse energy metabolism patterns in females in Neodon fuscus, Lasiopodomys brandtii, and Mus musculus revealed by comparative transcriptomics under hypoxic conditions

The effects of global warming and anthropogenic disturbance force animals to migrate from lower to higher elevations to find suitable new habitats. As such migrations increase hypoxic stress on the animals, it is important to understand how plateau- and plain-dwelling animals respond to low-oxygen environments. We used comparative transcriptomics to explore the response of Neodon fuscus, Lasiopodomys brandtii, and Mus musculus skeletal muscle tissues to hypoxic conditions. Results indicate that these species have adopted different oxygen transport and energy metabolism strategies for dealing with a hypoxic environment. N. fuscus promotes oxygen transport by increasing hemoglobin synthesis and reduces the risk of thrombosis through cooperative regulation of genes, including Fga, Fgb, Alb, and Ttr; genes such as Acs16, Gpat4, and Ndufb7 are involved in regulating lipid synthesis, fatty acid β-oxidation, hemoglobin synthesis, and electron-linked transmission, thereby maintaining a normal energy supply in hypoxic conditions. In contrast, the oxygen-carrying capacity and angiogenesis of red blood cells in L. brandtii are promoted by genes in the CYP and COL families; this species maintains its bodily energy supply by enhancing the pentose phosphate pathway and mitochondrial fatty acid synthesis pathway. However, under hypoxia, M. musculus cannot effectively transport additional oxygen; thus, its cell cycle, proliferation, and migration are somewhat affected. Given its lack of hypoxic tolerance experience, M. musculus also shows significantly reduced oxidative phosphorylation levels under hypoxic conditions. Our results suggest that the glucose capacity of M. musculus skeletal muscle does not provide sufficient energy during hypoxia; thus, we hypothesize that it supplements its bodily energy by synthesizing ketone bodies. For the first time, we describe the energy metabolism pathways of N. fuscus and L. brandtii skeletal muscle tissues under hypoxic conditions. Our findings, therefore, improve our understanding of how vertebrates thrive in high altitude and plain habitats when faced with hypoxic conditions.

Ion Channels, Transporters, and Sensors Interact with the Acidic Tumor Microenvironment to Modify Cancer Progression

Solid tumors, including breast carcinomas, are heterogeneous but typically characterized by elevated cellular turnover and metabolism, diffusion limitations based on the complex tumor architecture, and abnormal intra- and extracellular ion compositions particularly as regards acid-base equivalents. Carcinogenesis-related alterations in expression and function of ion channels and transporters, cellular energy levels, and organellar H⁺ sequestration further modify the acid-base composition within tumors and influence cancer cell functions, including cell proliferation, migration, and survival. Cancer cells defend their cytosolic pH and HCO₃^- concentrations better than normal cells when challenged with the marked deviations in extracellular H⁺, HCO₃^-, and lactate concentrations typical of the tumor microenvironment. Ionic gradients determine the driving forces for ion transporters and channels and influence the membrane potential. Cancer and stromal cells also sense abnormal ion concentrations via intra- and extracellular receptors that modify cancer progression and prognosis. With emphasis on breast cancer, the current review first addresses the altered ion composition and the changes in expression and functional activity of ion channels and transporters in solid cancer tissue. It then discusses how ion channels, transporters, and cellular sensors under influence of the acidic tumor microenvironment shape cancer development and progression and affect the potential of cancer therapies.

Is carbonic anhydrase inhibition useful as a complementary therapy of Covid-19 infection?

The ongoing Covid-19 is a contagious disease, and it is characterised by different symptoms such as fever, cough, and shortness of breath. Rising concerns about Covid-19 have severely affected the healthcare system in all countries as the Covid-19 outbreak has developed at a rapid rate all around the globe. Intriguing, a clinically used drug, acetazolamide (a specific inhibitor of carbonic anhydrase, CA, EC 4.2.1.1), is used to treat high-altitude pulmonary oedema (HAPE), showing a high degree of clinical similarities with the pulmonary disease caused by Covid-19. In this context, this preliminary study aims to provide insights into some factors affecting the Covid-19 patients, such as hypoxaemia, hypoxia as well as the blood CA activity. We hypothesise that patients with Covid-19 problems could show a dysregulated acid–base status influenced by CA activity. These preliminary results suggest that the use of CA inhibitors as a pharmacological treatment for Covid-19 may be beneficial.

Respiratory Dialysis-A Novel Low Bicarbonate Dialysate to Provide Extracorporeal CO2 Removal

OBJECTIVES

We designed a novel respiratory dialysis system to remove CO2 from blood in the form of bicarbonate. We aimed to determine if our respiratory dialysis system removes CO2 at rates comparable to low-flow extracorporeal CO2 removal devices (blood flow < 500 mL/min) in a large animal model.

DESIGN

Experimental study.

SETTING

Animal research laboratory.

SUBJECTS

Female Yorkshire pigs.

INTERVENTIONS

Five bicarbonate dialysis experiments were performed. Hypercapnia (PCO2 90-100 mm Hg) was established in mechanically ventilated swine by adjusting the tidal volume. Dialysis was then performed with a novel low bicarbonate dialysate.

MEASUREMENTS AND MAIN RESULTS

We measured electrolytes, blood gases, and plasma-free hemoglobin in arterial blood, as well as blood entering and exiting the dialyzer. We used a physical-chemical acid-base model to understand the factors influencing blood pH after bicarbonate removal. During dialysis, we removed 101 (±13) mL/min of CO2 (59 mL/min when normalized to venous PCO2 of 45 mm Hg), corresponding to a 29% reduction in PaCO2 (104.0 ± 8.1 vs 74.2 ± 8.4 mm Hg; p < 0.001). Minute ventilation and body temperature were unchanged during dialysis (1.2 ± 0.4 vs 1.1 ± 0.4 L/min; p = 1.0 and 35.3°C ± 0.9 vs 35.2°C ± 0.6; p = 1.0). Arterial pH increased after bicarbonate removal (7.13 ± 0.04 vs 7.21 ± 0.05; p < 0.001) despite no attempt to realkalinize the blood. Our modeling showed that dialysate electrolyte composition, plasma albumin, and plasma total CO2 accurately predict the measured pH of blood exiting the dialyser. However, the final effluent dose exceeded conventional doses, depleting plasma glucose and electrolytes, such as potassium and phosphate.

CONCLUSIONS

Bicarbonate dialysis results in CO2 removal at rates comparable with existing low-flow extracorporeal CO2 removal in a large animal model, but the final dialysis dose delivered needs to be reduced before the technique can be used for prolonged periods.

Water as a Blood Model for Determination of CO2 Removal Performance of Membrane Oxygenators

CO₂ removal via membrane oxygenators has become an important and reliable clinical technique. Nevertheless, oxygenators must be further optimized to increase CO₂ removal performance and to reduce severe side effects. Here, in vitro tests with water can significantly reduce costs and effort during development. However, they must be able to reasonably represent the CO₂ removal performance observed with blood. In this study, the deviation between the CO₂ removal rate determined in vivo with porcine blood from that determined in vitro with water is quantified. The magnitude of this deviation (approx. 10%) is consistent with results reported in the literature. To better understand the remaining difference in CO₂ removal rate and in order to assess the application limits of in vitro water tests, CFD simulations were conducted. They allow to quantify and investigate the influences of the differing fluid properties of blood and water on the CO₂ removal rate. The CFD results indicate that the main CO₂ transport resistance, the diffusional boundary layer, behaves generally differently in blood and water. Hence, studies of the CO₂ boundary layer should be preferably conducted with blood. In contrast, water tests can be considered suitable for reliable determination of the total CO₂ removal performance of oxygenators.

Molecular Characterization of Carbonic Anhydrase II (CA II) and Its Potential Involvement in Regulating Shell Formation in the Pacific Abalone, Haliotis discus hannai

Carbonic anhydrases (CAs) are a family of metalloenzymes that can catalyze the reversible interconversion of CO₂/HCO₃^–, ubiquitously present in both prokaryotes and eukaryotes. In the present study, a CA II (designated as HdhCA II) was sequenced and characterized from the mantle tissue of the Pacific abalone. The complete sequence of HdhCA II was 1,169 bp, encoding a polypeptide of 349 amino acids with a NH₂-terminal signal peptide and a CA architectural domain. The predicted protein shared 98.57% and 68.59% sequence identities with CA II of Haliotis gigantea and Haliotis tuberculata, respectively. Two putative N-linked glycosylation motifs and two cysteine residues could potentially form intramolecular disulfide bond present in HdhCA II. The phylogenetic analysis indicated that HdhCA II was placed in a gastropod clade and robustly clustered with CA II of H. gigantea and H. tuberculata. The highest level of HdhCA II mRNA expression was detected in the shell forming mantle tissue. During ontogenesis, the mRNA of HdhCA II was detected in all stages, with larval shell formation stage showing the highest expression level. The in situ hybridization results detected the HdhCA II mRNA expression in the epithelial cells of the dorsal mantle pallial, an area known to express genes involved in the formation of a nacreous layer in the shell. This is the first report of HdhCA II in the Pacific abalone, and the results of this study indicate that this gene might play a role in the shell formation of abalone.

Carbonic anhydrase seven bundles filamentous actin and regulates dendritic spine morphology and density

Intracellular pH is a potent modulator of neuronal functions. By catalyzing (de)hydration of CO2 , intracellular carbonic anhydrase (CAi ) isoforms CA2 and CA7 contribute to neuronal pH buffering and dynamics. The presence of two highly active isoforms in neurons suggests that they may serve isozyme-specific functions unrelated to CO2 -(de)hydration. Here, we show that CA7, unlike CA2, binds to filamentous actin, and its overexpression induces formation of thick actin bundles and membrane protrusions in fibroblasts. In CA7-overexpressing neurons, CA7 is enriched in dendritic spines, which leads to aberrant spine morphology. We identified amino acids unique to CA7 that are required for direct actin interactions, promoting actin filament bundling and spine targeting. Disruption of CA7 expression in neocortical neurons leads to higher spine density due to increased proportion of small spines. Thus, our work demonstrates highly distinct subcellular expression patterns of CA7 and CA2, and a novel, structural role of CA7.

Characterization and Comparative Transcriptomic Analysis of Skeletal Muscle in Pekin Duck at Different Growth Stages Using RNA-Seq

Simple Summary

Skeletal muscle is an important tissue and its development is strictly regulated by genes. In this study, in order to understand the muscle-related gene expression in Pekin duck, RNA-seq was performed to analyze and compare skeletal muscle at different growth stages. Alternative splicing, single nucleotide polymorphisms and insertion–deletions were detected, and 299 novel genes were discovered. MYL4, IGF2BP1, CSRP3, SPP1, KLHL31, LAMB2, LAMA2, ITGB1 and OPN played crucial roles in skeletal muscle development. Oxidative phosphorylation, ECM-receptor interaction, focal adhesion, carbon metabolism, and biosynthesis of amino acids participated in the regulation of skeletal muscle development in Pekin duck. This study provides an important reference for revealing the developmental mechanisms of pectoral and leg muscles in duck.

Abstract

Skeletal muscle, accounting for approximately 50% of body weight, is the largest and most important tissue. In this study, the gene expression profiles and pathways in skeletal muscle of Pekin duck were investigated and compared at embryonic day 17, 21, and 27 and postnatally at 6 months of age. An average of 49,555,936 reads in each sample was obtained from the transcriptome libraries. Over 70.0% of alternative splicing (AS) in each sample was mainly alternative 5′ first exon (transcription start site)—the first exon splicing (TSS) and alternative 3′ last exon (transcription terminal site)—the last exon splicing (TTS), indicating that TSS and TTS were the most common AS event in Pekin ducks, and these AS events were closely related to the regulation of muscle development at different growth stages. The results provided a valuable genomic resource for selective breeding and functional studies of genes. A total of 299 novel genes with ≥2 exons were obtained. There were 294 to 2806 differentially expressed genes (DEGs) in each pairwise comparison of Pekin duck. Notably, 90 DEGs in breast muscle and 9 DEGs in leg muscle were co-expressed at all developmental points. DEGs were validated by qPCR analysis, which confirmed the tendency of the expression. DEGs related to muscle development were involved in biological processes such as “endodermal cell differentiation”, “muscle cell cellular homeostasis”, “skeletal muscle tissue growth” and “skeletal muscle cell differentiation”, and were involved in pathways such as oxidative phosphorylation, ECM-receptor (extracellular matrix receptor) interaction, focal adhesion, carbon metabolism, and biosynthesis of amino acids. Some DEGs, including MYL4, IGF2BP1, CSRP3, SPP1 and KLHL31, as well as LAMB2, LAMA2, ITGB1 and OPN, played crucial roles in muscle growth and development. This study provides valuable information about the expression profile of mRNAs and pathways from duck skeletal muscle at different growth stages, and further functional study of these mRNAs and pathways could provide new ideas for studying the molecular networks of growth and development in duck skeletal muscle.

Stepping stones to the future of haemoglobin-based blood products: clinical, preclinical and innovative examples

Critical overview of the different oxygen therapeutics developed so far to be used when donor blood is not available.

Influences of Blood Lactate Levels on Cognitive Domains and Physical Health during a Sports Stress. Brief Review

The present review aims to examine the effects of high blood lactate levels in healthy adult humans, for instance, after a period of exhaustive exercise, on the functioning of the cerebral cortex. In some of the examined studies, high blood lactate levels were obtained not only through exhaustive exercise but also with an intravenous infusion of lactate while the subject was immobile. This allowed us to exclude the possibility that the observed post-exercise effects were nonspecific (e.g., cortical changes in temperature, acidity, etc.). We observed that, in both experimental conditions, high levels of blood lactate are associated with a worsening of important cognitive domains such as attention or working memory or stress, without gender differences. Moreover, in both experimental conditions, high levels of blood lactate are associated with an improvement of the primary motor area (M1) excitability. Outside the frontal lobe, the use of visual evoked potentials and somatosensory evoked potentials allowed us to observe, in the occipital and parietal lobe respectively, that high levels of blood lactate are associated with an amplitude’s increase and a latency’s reduction of the early components of the evoked responses. In conclusion, significant increases of blood lactate levels could exercise a double-action in the central nervous system (CNS), with a protecting role on primary cortical areas (such as M1, primary visual area, or primary somatosensory cortex), while reducing the efficiency of adjacent regions, such as the supplementary motor area (SMA) or prefrontal cortex. These observations are compatible with the possibility that lactate works in the brain not only as an energy substrate or an angiogenetic factor but also as a true neuromodulator, which can protect from stress. In this review, we will discuss the mechanisms and effects of lactic acid products produced during an anaerobic exercise lactate, focusing on their action at the level of the central nervous system with particular attention to the primary motor, the somatosensory evoked potentials, and the occipital and parietal lobe.

Facemasks simple but powerful weapons to protect against COVID-19 spread: Can they have sides effects?

In the last few months, the spread of COVID-19 among humans has caused serious damages around the globe letting many countries economically unstable. Results obtained from conducted research by epidemiologists and virologists showed that, COVID-19 is mainly spread from symptomatic individuals to others who are in close contact via respiratory droplets, mouth and nose, which are the primary mode of transmission. World health organization regulations to help stop the spread of this deadly virus, indicated that, it is compulsory to utilize respiratory protective devices such as facemasks in the public. Indeed, the use of these facemasks around the globe has helped reduce the spread of COVID-19. The primary aim of facemasks, is to avoid inhaling air that could contain droplets with COVID-19. We should note that, respiration process is the movement of oxygen from external atmosphere to the cells within tissue and the transport of carbon dioxide outside. However, the rebreathing of carbon dioxide using a facemask has not been taken into consideration. The hypercapnia (excess inhaled content of CO2) has been recognized to be related to symptoms of fatigue, discomfort, muscular weakness, headaches as well as drowsiness. Rebreathing of CO2 has been a key to concern regarding the use of a facemask. Rebreathing usually occur when an expired air that is rich in CO2 stays long than normal in the breathing space of the respirator after a breath. The increase of the arterial CO2 concentration leads to symptoms that are aforementioned. Studies have been conducted on facemask shortages and on the appropriate facemask required to reduce the spread of COVID-19; however no study has been conducted to assess the possible relationship between CO2 inhalation due to facemask, to determine and recommend which mask is appropriate in the reduction of the spread of the coronavirus while simultaneously avoid CO2 inhalation by the facemask users. In the current paper, we provided a literature review on the use of facemasks with the aim to determine which facemasks could be used to avoid re-inhaling rejected CO2. Additionally, we presented mathematical models depicting the transport of COVID-19 spread through wind with high speed. We considered first mathematical models for which the effect air-heterogeneity is neglected, such that air flow follows Markovian process with a retardation factor, these models considered two different scenarios, the speed of wind is constant and time-space dependent. Secondly, we assumed that the wind movement could follow different processes, including the power law process, fading memory process and a two-stage processes, these lead us to use differential operators with power law, exponential decay and the generalized Mittag-Leffler function with the aim to capture these processes. A numerical technique based on the Lagrange polynomial interpolation was used to solve some of these models numerically. The numerical solutions were coded in MATLAB software for simulations. The results obtained from the mathematical simulation showed that a wind with speed of 100 km/h could transport droplets as far as 300 m. The results obtained from these simulations together with those presented by other researchers lead us to conclude that, the wind could have helped spread COVID-19 in some places around the world, especially in coastal areas. Therefore, appropriate facemasks that could help avoid re-inhaling enough CO2 should be used every time one is in open air even when alone especially in windy environment.

Radiotracers for positron emission tomography (PET) targeting tumour-associated carbonic anhydrase isoforms

The tumour-associated, cell membrane-bound isoforms IX and XII of human carbonic anhydrase (CA, EC 4.2.1.1) are overexpressed in cancer cells contributing to the hypoxic tumour pH/metabolism regulating machinery and as thus, can serve as markers of malignant neoplastic tissue. Inhibitors of CAs can be employed both for the treatment of hypoxic tumours and in the design of radiotracers for positron emission tomography and imaging of such cancers. The present review provides a comprehensive summary of the progress achieved to-date in the field of developing PET-tracers based on monoclonal antibodies, biomolecules, and small-molecule ligands of CA IX and XII.

Pathophysiology of respiratory failure and physiology of gas exchange during ECMO

Lungs play a key role in sustaining cellular respiration by regulating the levels of oxygen and carbon dioxide in the blood. This is achieved by exchanging these gases between blood and ambient air across the alveolar capillary membrane by the process of diffusion. In the microstructure of the lung, gas exchange is compartmentalized and happens in millions of microscopic alveolar units. In situations of lung injury, this structural complexity is disrupted resulting in impaired gas exchange. Depending on the severity and the type of lung injury, different aspects of pulmonary physiology are affected. If the respiratory failure is refractory to ventilator support, extracorporeal membrane oxygenation (ECMO) can be utilized to support the gas exchange needs of the body. In ECMO, thin hollow fiber membranes made up of polymethylpentene act as blood-gas interface for diffusion. Decades of innovative engineering with membranes and their alignment with blood and gas flows has enabled modern oxygenators to achieve clinically and physiologically significant amount of gas exchange.

Measuring hemoglobin spectra: searching for carbamino-hemoglobin

SIGNIFICANCE

The arterial carbon dioxide (CO2) partial pressure PaCO2 is a clinically relevant variable. However, its measurement requires arterial blood sampling or bulky and expensive transcutaneous PtcCO2 meters. While the spectrophotometric determination of hemoglobin species-such as oxy-hemoglobin (O2Hb) and deoxy-hemoglobin (HHb)-allowed for the development of pulse oximetry, the measurement of CO2 blood content with minimal discomfort has not been addressed yet.

AIM

Characterizing human carbamino-hemoglobin (CO2Hb) absorption spectrum, which is missing from the literature. Providing the theoretical background that will allow for transcutaneous, noninvasive PaCO2 measurements.

APPROACH

A tonometry-based approach was used to obtain gas-equilibrated, lysed, diluted human blood. Equilibration was performed with both CO2, dinitrogen (N2), and ambient air. Spectrophotometric measurements were carried out on the 235- to 1000-nm range. A theoretical background was also derived from that of pulse oximetry.

RESULTS

The absorption spectra of both CO2Hb and HHb were extremely close and comparable with that of state-of-the-art HHb. The above-mentioned theoretical background led to an estimated relative error above 30% on the measured amount of CO2Hb in a subject's blood. Auxiliary measurements revealed that the use of ethylene diamine tetraacetic acid did not interfere with spectrophotometric measurements, whereas sodium metabisulfite did.

CONCLUSIONS

CO2Hb absorption spectrum was measured for the first time. Such spectrum being close to that of HHb, the use of a theoretical background based on pulse oximetry theory for noninvasive PaCO2 measurement seems extremely challenging.

Extracorporeal CO2 Removal Integrated within a Continuous Renal Replacement Circuit Offers Multiple Advantages

Extracorporeal CO2 removal within a continuous renal replacement therapy circuit offers multiple advantages for the regulation of the CO2 extraction. The authors review the impact of the dialysate solution, the buffer, and the anticoagulation on CO2 removal. They propose a theoretical model of the ideal circuit for the optimization of CO2 extraction.

In vitro application of carbonic anhydrase to accelerate the equilibration of 18O between H2O and CO2 for the rapid measurement of 18O/16O isotope ratios in aqueous samples

A novel method of the accelerated equilibration of ¹⁸O between CO₂ and H₂O for the measurement of the ¹⁸O/¹⁶O isotope ratios in aqueous samples with natural isotope abundances is presented. This rapid equilibrium method is based on the in vitro application of the enzyme carbonic anhydrase (CA). The CA from bovine erythrocytes was adsorptively fixed to 3-mm glass beads with an etched surface. After the addition of this carrier-fixed CA catalyst to the water sample, the isotope equilibrium was already reached after 1 h. The previously used non-catalysed ¹⁸O isotope exchange in water samples needs about 24 h. Whole blood samples also showed fast ¹⁸O isotope equilibration, which definitely results from the native presence of CA in erythrocytes. By shortening the time for sample preparation, the CA catalysed technique can significantly increase the throughput of the samples to be measured, and also ¹⁸O and ²H measurement by means of isotope ratio mass spectrometry (IRMS) may be synchronized. The ²H and ¹⁸O sample preparation can be performed in the same reaction vessel because cross-effects at the simultaneous use of Pt and CA catalysts do not occur.

A Proof of Concept Study, Demonstrating Extracorporeal Carbon Dioxide Removal Using Hemodialysis with a Low Bicarbonate Dialysate

Extracorporeal carbon dioxide removal (ECCO2R) devices remove CO2 directly from blood, facilitating ultraprotective ventilation or even providing an alternative to mechanical ventilation. However, ECCO2R is not widely available, whereas dialysis is available in most intensive care units (ICUs). Prior attempts to provide ECCO2R with dialysis, by removing CO2 in the form of bicarbonate, have been plagued by metabolic acidosis. We hypothesized that bicarbonate dialysis is feasible, provided the plasma strong ion difference is maintained. We used a mathematical model to investigate the effects of bicarbonate removal on pH and CO2 in plasma, and performed in-vitro experiments to test CO2 removal using three dialysates with different bicarbonate concentrations (0, 16, and 32 mmol·L). Our modeling predicted a reduction in partial pressures of CO2 (PCO2) and increased pH with progressive lowering of plasma bicarbonate, provided strong ion difference and plasma proteins (Atot) were maintained. In our in-vitro experiments, total CO2 removal, scaled up to an adult size filter, was highest with our dialysate containing no bicarbonate, where we removed the equivalent of 94 ml·min (±3.0) of CO2. Under the same conditions, our dialysate containing a conventional bicarbonate concentration (32 mmol·L) only removed 5 ml·min (±4; p < 0.001). As predicted, pH increased following bicarbonate removal. Our data show that dialysis using low bicarbonate dialysates is feasible and results in a reduction in plasma PCO2. When scaled up, to estimate equivalent CO2 removal with an adult dialysis circuit, the amount removed competes with existing low-flow ECCO2R devices.

Proteomic Characterization of Normal and Woody Breast Meat from Broilers of Five Genetic Strains

Woody breast (WB) is an emergent broiler myopathy that is macroscopically characterized by hardened areas of the Pectoralis major muscle. Five genetic strains (strains 1–5) of mixed-sex broilers were fed either a control or an amino acid (AA)-reduced diet (20% reduction of digestible lysine, total sulfur AAs, and threonine) for 8 wk. Differences between whole-muscle proteome profiles of normal breast (NB; n = 6 gels) and WB tissue (n = 6 gels) were characterized for (1) broiler strains 1–5 that were fed with a control diet and collected at 0 min; (2) strain 5 (control diet) that were collected at 15 min, 4 h, and 24 h; (3) strain 5 (0 min) that were fed with a control and an AA-reduced diet. Birds that yielded WB were heavier and had a greater pH at death (pH0min) than normal birds. Results indicated that 21 proteins were more abundant (P &lt; 0.05) and 3 proteins were less abundant (P &lt; 0.05) in WB compared with NB. The differentially abundant proteins in each comparison were consistently upregulated or downregulated in WB tissue although the different protein profiles were noticed for each comparison. Strains 2 and 5 had more protein profile differences between WB and NB meat than strains 1, 3, and 4, which potentially indicates a stronger genetic component for strains 2 and 5 with respect to WB formation. The proteins that were more abundant in WB compared to NB are involved in carbohydrate metabolism, oxidative stress, cytoskeleton structure, and transport and signaling. Ingenuity Pathway Analysis indicated that regulated pathways in WB were mainly related to carbohydrate metabolism, cellular repair, cellular organization and maintenance, and cell death and survival. The results support the potential causes of WB myopathy, including the presence of hypoxia, oxidative stress, increased apoptosis, misfolded proteins, and inflammation.

Insights on the Functions and Ecophysiological Relevance of the Diverse Carbonic Anhydrases in Microalgae

Carbonic anhydrases (CAs) exist in all kingdoms of life. They are metalloenzymes, often containing zinc, that catalyze the interconversion of bicarbonate and carbon dioxide-a ubiquitous reaction involved in a variety of cellular processes. So far, eight classes of apparently evolutionary unrelated CAs that are present in a large diversity of living organisms have been described. In this review, we focus on the diversity of CAs and their roles in photosynthetic microalgae. We describe their essential role in carbon dioxide-concentrating mechanisms and photosynthesis, their regulation, as well as their less studied roles in non-photosynthetic processes. We also discuss the presence in some microalgae, especially diatoms, of cambialistic CAs (i.e., CAs that can replace Zn by Co, Cd, or Fe) and, more recently, a CA that uses Mn as a metal cofactor, with potential ecological relevance in aquatic environments where trace metal concentrations are low. There has been a recent explosion of knowledge about this well-known enzyme with exciting future opportunities to answer outstanding questions using a range of different approaches.

Single-cell O2 exchange imaging shows that cytoplasmic diffusion is a dominant barrier to efficient gas transport in red blood cells

Blood is routinely tested for gas-carrying capacity (total hemoglobin), but this cannot determine the speed at which red blood cells (RBCs) exchange gases. Such information is critical for evaluating the physiological fitness of RBCs, which have very limited capillary transit times (<1 s) for turning over substantial volumes of gas. We developed a method to quantify gas exchange in individual RBCs and used it to show that restricted diffusion, imposed by hemoglobin crowding, is a major barrier to gas flows. Consequently, hematological disorders manifesting a change in cell shape or hemoglobin concentration have uncharted implications on gas exchange, which we illustrate using inherited anemias. With its single-cell resolution, the method can identify physiologically inferior subpopulations, providing a clinically useful appraisal of blood quality.

Disorders of oxygen transport are commonly attributed to inadequate carrying capacity (anemia) but may also relate to inefficient gas exchange by red blood cells (RBCs), a process that is poorly characterized yet assumed to be rapid. Without direct measurements of gas exchange at the single-cell level, the barriers to O₂ transport and their relationship with hematological disorders remain ill defined. We developed a method to track the flow of O₂ in individual RBCs by combining ultrarapid solution switching (to manipulate gas tension) with single-cell O₂ saturation fluorescence microscopy. O₂ unloading from RBCs was considerably slower than previously estimated in acellular hemoglobin solutions, indicating the presence of diffusional barriers in intact cells. Rate-limiting diffusion across cytoplasm was demonstrated by osmotically induced changes to hemoglobin concentration (i.e., diffusive tortuosity) and cell size (i.e., diffusion pathlength) and by comparing wild-type cells with hemoglobin H (HbH) thalassemia (shorter pathlength and reduced tortuosity) and hereditary spherocytosis (HS; expanded pathlength). Analysis of the distribution of O₂ unloading rates in HS RBCs identified a subpopulation of spherocytes with greatly impaired gas exchange. Tortuosity imposed by hemoglobin was verified by demonstrating restricted diffusivity of CO₂, an acidic gas, from the dissipative spread of photolytically uncaged H⁺ ions across cytoplasm. Our findings indicate that cytoplasmic diffusion, determined by pathlength and tortuosity, is a major barrier to efficient gas handling by RBCs. Consequently, changes in RBC shape and hemoglobin concentration, which are common manifestations of hematological disorders, can have hitherto unrecognized and clinically significant implications on gas exchange.

The importance of a single amino acid substitution in reduced red blood cell carbonic anhydrase function of early-diverging fish

In most vertebrates, red blood cell carbonic anhydrase (RBC CA) plays a critical role in carbon dioxide (CO₂) transport and excretion across epithelial tissues. Many early-diverging fishes (e.g., hagfish and chondrichthyans) are unique in possessing plasma-accessible membrane-bound CA-IV in the gills, allowing some CO₂ excretion to occur without involvement from the RBCs. However, implications of this on RBC CA function are unclear. Through homology cloning techniques, we identified the putative protein sequences for RBC CA from nine early-diverging species. In all cases, these sequences contained a modification of the proton shuttle residue His-64, and activity measurements from three early-diverging fish demonstrated significantly reduced CA activity. Site-directed mutagenesis was used to restore the His-64 proton shuttle, which significantly increased RBC CA activity, clearly illustrating the functional significance of His-64 in fish red blood cell CA activity. Bayesian analyses of 55 vertebrate cytoplasmic CA isozymes suggested that independent evolutionary events led to the modification of His-64 and thus reduced CA activity in hagfish and chondrichthyans. Additionally, in early-diverging fish that possess branchial CA-IV, there is an absence of His-64 in RBC CAs and the absence of the Root effect [where a reduction in pH reduces hemoglobin's capacity to bind with oxygen (O₂)]. Taken together, these data indicate that low-activity RBC CA may be present in all fish with branchial CA-IV, and that the high-activity RBC CA seen in most teleosts may have evolved in conjunction with enhanced hemoglobin pH sensitivity.

The effects of severe hemoconcentration on acid-base equilibrium in critically ill patients: the forgotten role of buffers in whole blood

PURPOSE

Idiopathic Systemic Capillary Leak Syndrome (ISCLS) is a paroxysmal permeability disorder characterized by abrupt onset of shock and hemoconcentration due to massive shift of fluids and proteins from the intravascular to the interstitial compartment. We hypothesize that increased hemoglobin concentration has a pivotal role in the acid-base imbalance during life-threatening crises.

MATERIALS AND METHODS

Analysis of the acid-base balance fluctuations during six severe ISCLS flares admitted to ICU of a referral center for ISCLS.

RESULTS

Acid-base equilibrium was assessed for plasma and the whole blood by single and multicompartmental models. The acute phase of ISCLS was characterized by shock, hypoalbuminemia, severe hemoconcentration, and acidosis. The physical-chemical approach for plasma found a remarkable component of unmeasured anions (SIG) during the acute phase. After correction of the physical-chemical model for the whole blood, the SIG variations disappeared because the buffer role of hemoglobin was relevant.

CONCLUSION

Hemoglobin has a remarkable role in buffering metabolic acidosis during the shock phase of ISCLS. In these circumstances, the assessment of acid-base equilibrium in plasma alone may overestimate unmeasured anions. On the contrary, the physical-chemical model corrected for whole blood better explains the metabolic component of acid-base imbalance when marked shift of hemoglobin concentration occurs.

In silico study of the role of cell growth factors in photosynthesis using a virtual leaf tissue generator coupled to a microscale photosynthesis gas exchange model

Computational tools that allow in silico analysis of the role of cell growth and division on photosynthesis are scarce. We present a freely available tool that combines a virtual leaf tissue generator and a two-dimensional microscale model of gas transport during C3 photosynthesis. A total of 270 mesophyll geometries were generated with varying degrees of growth anisotropy, growth extent, and extent of schizogenous airspace formation in the palisade mesophyll. The anatomical properties of the virtual leaf tissue and microscopic cross-sections of actual leaf tissue of tomato (Solanum lycopersicum L.) were statistically compared. Model equations for transport of CO2 in the liquid phase of the leaf tissue were discretized over the geometries. The virtual leaf tissue generator produced a leaf anatomy of tomato that was statistically similar to real tomato leaf tissue. The response of photosynthesis to intercellular CO2 predicted by a model that used the virtual leaf tissue geometry compared well with measured values. The results indicate that the light-saturated rate of photosynthesis was influenced by interactive effects of extent and directionality of cell growth and degree of airspace formation through the exposed surface of mesophyll per leaf area. The tool could be used further in investigations of improving photosynthesis and gas exchange in relation to cell growth and leaf anatomy.

Ocean Acidification and Coastal Marine Invertebrates: Tracking CO2 Effects from Seawater to the Cell

In the last few decades, numerous studies have investigated the impacts of simulated ocean acidification on marine species and communities, particularly those inhabiting dynamic coastal systems. Despite these research efforts, there are many gaps in our understanding, particularly with respect to physiological mechanisms that lead to pathologies. In this review, we trace how carbonate system disturbances propagate from the coastal environment into marine invertebrates and highlight mechanistic links between these disturbances and organism function. We also point toward several processes related to basic invertebrate biology that are severely understudied and prevent an accurate understanding of how carbonate system dynamics influence organismic homeostasis and fitness-related traits. We recommend that significant research effort be directed to studying cellular phenotypes of invertebrates acclimated or adapted to elevated seawater pCO₂ using biochemical and physiological methods.

Comparison of blood carbonic anhydrase activity of athletes performing interval and continuous running exercise at high altitude

The effects of high-intensity interval and continuous exercise on erythrocytes carbonic anhydrase (CA, EC 4.2.1.1) activity levels were scarcely investigated up until now. Here we present a study focused on the CA activity from erythrocytes of athletes experiencing interval and continuous training for 6 weeks, during cold weather and at high altitude (> 1600 m). We observed a 50% increase in the blood CA activity at the second week after initiation of the training in both interval and continuos running groups, whereas the control group did not experience any variation in the enzyme activity levels. In the trained individuals a mild decrease in their body mass, BMI and an increased [Formula: see text] were also observed. The CA activity returned at the basal values after 4-6 weeks after the training started, probably proving that a metabolic compensation occurred without the need of an enhanced enzyme activity. The unexpected 50% rise of activity for an enzyme which acts as a very efficient catalyst for CO2 hydration/bicarbonate dehydration, such as the blood CA, deserves further investigations for better understanding the physiologic basis of this phenomenon.

Visualising reactive oxygen species in live mammals and revealing of ROS-related system

Of all the aerobic respiration by-products, cytotoxic superoxide derived from mitochondrial-leaked electrons, is the only one known to be disposed of intracellularly. Is this fate the only destiny for mitochondrial-leaked electrons? When Cynomolgus monkeys were injected intravenously with reactive oxygen species (ROS) indicators, the connective tissues of dura mater, facial fascia, pericardium, linea alba, dorsa fascia and other body parts, emitted specific and intense fluorescent signals. Moreover, the fluorescent signals along the linea alba of SD rats, did not result from the local presence of ROS but from the interaction of ROS indicators with electrons flowing through this tissue. Furthermore, the electrons travelling along the linea alba of mice were revealed to originate from mitochondria. These data suggest that mitochondrial-leaked electrons may be transported extracellularly to a hitherto undescribed system of connective tissues, which is pervasively networked, electrically conductive and metabolically related.

Intact carbonic acid is a viable protonating agent for biological bases

Carbonic acid H2CO3 (CA) is a key constituent of the universal CA/bicarbonate/CO2 buffer maintaining the pH of both blood and the oceans. Here we demonstrate the ability of intact CA to quantitatively protonate bases with biologically-relevant pKas and argue that CA has a previously unappreciated function as a major source of protons in blood plasma. We determine with high precision the temperature dependence of pKa(CA), pKa(T) = -373.604 + 16,500/T + 56.478 ln T. At physiological-like conditions pKa(CA) = 3.45 (I = 0.15 M, 37 °C), making CA stronger than lactic acid. We further demonstrate experimentally that CA decomposition to H2O and CO2 does not impair its ability to act as an ordinary carboxylic acid and to efficiently protonate physiological-like bases. The consequences of this conclusion are far reaching for human physiology and marine biology. While CA is somewhat less reactive than (H+)aq, it is more than 1 order of magnitude more abundant than (H+)aq in the blood plasma and in the oceans. In particular, CA is about 70× more abundant than (H+)aq in the blood plasma, where we argue that its overall protonation efficiency is 10 to 20× greater than that of (H+)aq, often considered to be the major protonating agent there. CA should thus function as a major source for fast in vivo acid-base reactivity in the blood plasma, possibly penetrating intact into membranes and significantly helping to compensate for (H+)aq's kinetic deficiency in sustaining the large proton fluxes that are vital for metabolic processes and rapid enzymatic reactions.

Exploring new structural features of the 4-[(3-methyl-4-aryl-2,3-dihydro-1,3-thiazol-2-ylidene)amino]benzenesulphonamide scaffold for the inhibition of human carbonic anhydrases

A library of 4-[(3-methyl-4-aryl-2,3-dihydro-1,3-thiazol-2-ylidene)amino]benzene-1-sulphonamides (EMAC8002a–m) was designed and synthesised to evaluate the effect of substituents in the positions 3 and 4 of the dihydrothiazole ring on the inhibitory potency and selectivity toward human carbonic anhydrase isoforms I, II, IX, and XII. Most of the new compounds preferentially inhibit the isoforms II and XII. Both electronic and steric features on the aryl substituent in the position 4 of the dihydrothiazole ring concur to determine the overall biological activity of these new derivatives.

Link between Heterotrophic Carbon Fixation and Virulence in the Porcine Lung Pathogen Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae is a capnophilic pathogen of the porcine respiratory tract lacking enzymes of the oxidative branch of the tricarboxylic acid (TCA) cycle. We previously claimed that A. pleuropneumoniae instead uses the reductive branch in order to generate energy and metabolites. Here, we show that bicarbonate and oxaloacetate supported anaerobic growth of A. pleuropneumoniae Isotope mass spectrometry revealed heterotrophic fixation of carbon from stable isotope-labeled bicarbonate by A. pleuropneumoniae, which was confirmed by nano-scale secondary ion mass spectrometry at a single-cell level. By gas chromatography-combustion-isotope ratio mass spectrometry we could further show that the labeled carbon atom is mainly incorporated into the amino acids aspartate and lysine, which are derived from the TCA metabolite oxaloacetate. We therefore suggest that carbon fixation occurs at the interface of glycolysis and the reductive branch of the TCA cycle. The heme precursor δ-aminolevulinic acid supported growth of A. pleuropneumoniae, similar to bicarbonate, implying that anaplerotic carbon fixation is needed for heme synthesis. However, deletion of potential carbon-fixing enzymes, including PEP-carboxylase (PEPC), PEP-carboxykinase (PEPCK), malic enzyme, and oxaloacetate decarboxylase, as well as various combinations thereof, did not affect carbon fixation. Interestingly, generation of a deletion mutant lacking all four enzymes was not possible, suggesting that carbon fixation in A. pleuropneumoniae is an essential metabolic pathway controlled by a redundant set of enzymes. A double deletion mutant lacking PEPC and PEPCK was not impaired in carbon fixation in vitro but showed reduction of virulence in a pig infection model.

Role of Carbonic Anhydrases and Inhibitors in Acid-Base Physiology: Insights from Mathematical Modeling

Carbonic anhydrases (CAs) catalyze a reaction fundamental for life: the bidirectional conversion of carbon dioxide (CO2) and water (H2O) into bicarbonate (HCO3-) and protons (H+). These enzymes impact numerous physiological processes that occur within and across the many compartments in the body. Within compartments, CAs promote rapid H+ buffering and thus the stability of pH-sensitive processes. Between compartments, CAs promote movements of H+, CO2, HCO3-, and related species. This traffic is central to respiration, digestion, and whole-body/cellular pH regulation. Here, we focus on the role of mathematical modeling in understanding how CA enhances buffering as well as gradients that drive fluxes of CO2 and other solutes (facilitated diffusion). We also examine urinary acid secretion and the carriage of CO2 by the respiratory system. We propose that the broad physiological impact of CAs stem from three fundamental actions: promoting H+ buffering, enhancing H+ exchange between buffer systems, and facilitating diffusion. Mathematical modeling can be a powerful tool for: (1) clarifying the complex interdependencies among reaction, diffusion, and protein-mediated components of physiological processes; (2) formulating hypotheses and making predictions to be tested in wet-lab experiments; and (3) inferring data that are impossible to measure.

Spatiotemporal pH Heterogeneity as a Promoter of Cancer Progression and Therapeutic Resistance

Dysregulation of pH in solid tumors is a hallmark of cancer. In recent years, the role of altered pH heterogeneity in space, between benign and aggressive tissues, between individual cancer cells, and between subcellular compartments, has been steadily elucidated. Changes in temporal pH-related processes on both fast and slow time scales, including altered kinetics of bicarbonate-CO₂ exchange and its effects on pH buffering and gradual, progressive changes driven by changes in metabolism, are further implicated in phenotypic changes observed in cancers. These discoveries have been driven by advances in imaging technologies. This review provides an overview of intra- and extracellular pH alterations in time and space reflected in cancer cells, as well as the available technology to study pH spatiotemporal heterogeneity.

How can CO2-derived indices guide resuscitation in critically ill patients?

Assessing the adequacy of oxygen delivery with oxygen requirements is one of the key-goal of haemodynamic resuscitation. Clinical examination, lactate and central or mixed venous oxygen saturation (S_vO₂ and S_cvO₂, respectively) all have their limitations. Many of them may be overcome by the use of the carbon dioxide (CO₂)-derived variables. The venoarterial difference in CO₂ tension ("ΔPCO₂" or "PCO₂ gap") is not an indicator of anaerobic metabolism since it is influenced by the oxygen consumption. By contrast, it reliably indicates whether blood flow is sufficient to carry CO₂ from the peripheral tissue to the lungs in view of its clearance: it, thus, reflects the adequacy of cardiac output with the metabolic condition. The ratio of the PCO₂ gap with the arteriovenous difference of oxygen content (PCO₂ gap/C_a-vO₂) might be a marker of anaerobiosis. Conversely to S_vO₂ and S_cvO₂, it remains interpretable if the oxygen extraction is impaired as it is in case of sepsis. Compared to lactate, it has the main advantage to change without delay and to provide a real-time monitoring of tissue hypoxia.

Clinical use of volumetric capnography in mechanically ventilated patients

Capnography is a first line monitoring system in mechanically ventilated patients. Volumetric capnography supports noninvasive and breath-by-breath information at the bedside using mainstream CO₂ and flow sensors placed at the airways opening. This volume-based capnography provides information of important body functions related to the kinetics of carbon dioxide. Volumetric capnography goes one step forward standard respiratory mechanics and provides a new dimension for monitoring of mechanical ventilation. The article discusses the role of volumetric capnography for the clinical monitoring of mechanical ventilation.

Using bidirectional chemical exchange for improved hyperpolarized [13 C]bicarbonate pH imaging

PURPOSE

Rapid chemical exchange can affect SNR and pH measurement accuracy for hyperpolarized pH imaging with [¹³ C]bicarbonate. The purpose of this work was to investigate chemical exchange effects on hyperpolarized imaging sequences to identify optimal sequence parameters for high SNR and pH accuracy.

METHODS

Simulations were performed under varying rates of bicarbonate-CO₂ chemical exchange to analyze exchange effects on pH quantification accuracy and SNR under different sampling schemes. Four pulse sequences, including 1 new technique, a multiple-excitation 2D EPI (multi-EPI) sequence, were compared in phantoms using hyperpolarized [¹³ C]bicarbonate, varying parameters such as tip angles, repetition time, order of metabolite excitation, and refocusing pulse design. In vivo hyperpolarized bicarbonate-CO₂ exchange measurements were made in transgenic murine prostate tumors to select in vivo imaging parameters.

RESULTS

Modeling of bicarbonate-CO₂ exchange identified a multiple-excitation scheme for increasing CO₂ SNR by up to a factor of 2.7. When implemented in phantom imaging experiments, these sampling schemes were confirmed to yield high pH accuracy and SNR gains. Based on measured bicarbonate-CO₂ exchange in vivo, a 47% CO₂ SNR gain is predicted.

CONCLUSION

The novel multi-EPI pulse sequence can boost CO₂ imaging signal in hyperpolarized ¹³ C bicarbonate imaging while introducing minimal pH bias, helping to surmount a major hurdle in hyperpolarized pH imaging.

Physiological effects of partial amniotic carbon dioxide insufflation with cold, dry vs heated, humidified gas in a sheep model

OBJECTIVE

Partial amniotic carbon dioxide (CO₂ ) insufflation (PACI) is used to improve visualization and facilitate complex fetoscopic surgery. However, there are concerns about fetal hypercapnic acidosis and postoperative fetal membrane inflammation. We assessed whether using heated and humidified, rather than cold and dry, CO₂ might reduce the impact of PACI on the fetus and fetal membranes in sheep.

METHODS

Twelve fetal lambs of 105 days' gestational age (term = 145 days) were exteriorized partially, via a midline laparotomy and hysterotomy, and arterial catheters and flow probes were inserted surgically. The 10 surviving fetuses were returned to the uterus, which was then closed and insufflated with cold, dry (22 °C at 0-5% humidity, n = 5) or heated, humidified (40 °C at 100% humidity, n = 5) CO₂ at 15 mmHg for 180 min. Fetal membranes were collected immediately after insufflation for histological analysis. Physiological data and membrane leukocyte counts, suggestive of membrane inflammation, were compared between the two groups.

RESULTS

After 180 min of insufflation, fetal survival was 0% in the group which underwent PACI with cold, dry CO₂ , and 60% (n = 3) in the group which received heated, humidified gas. While all insufflated fetuses became progressively hypercapnic (PaCO₂  > 68 mmHg), this was considerably less pronounced in those in which heated, humidified gas was used: after 120 min of insufflation, compared with those receiving cold, dry gas (n = 3), fetuses undergoing heated, humidified PACI (n = 5) had lower arterial partial pressure of CO₂ (mean ± standard error of the mean, 82.7 ± 9.1 mmHg for heated, humidified CO₂ vs 170.5 ± 28.5 for cold, dry CO₂ during PACI, P < 0.01), lower lactate levels (1.4 ± 0.4 vs 8.5 ± 0.9 mmol/L, P < 0.01) and higher pH (pH, 7.10 ± 0.04 vs 6.75 ± 0.04, P < 0.01). There was also a non-significant trend for fetal carotid artery pressure to be higher following PACI with heated, humidified compared with cold, dry CO₂ (30.5 ± 1.3 vs 8.7 ± 5.5 mmHg, P = 0.22). Additionally, the median (interquartile range) number of leukocytes in the chorion was significantly lower in the group undergoing PACI with heated, humidified CO₂ compared with the group receiving cold, dry CO₂ (0.7 × 10^-5 (0.5 × 10^-5 ) vs 3.2 × 10^-5 (1.8 × 10^-5 ) cells per square micron, P = 0.02).

CONCLUSIONS

PACI with cold, dry CO₂ causes hypercapnia, acidosis, hypotension and fetal membrane inflammation in fetal sheep, raising potential concerns for its use in humans. It seems that using heated, humidified CO₂ for insufflation partially mitigates these effects and this may be a suitable alternative for reducing the risk of fetal acid-base disturbances during, and fetal membrane inflammation following, complex fetoscopic surgery. © 2018 The Authors. Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of the International Society of Ultrasound in Obstetrics and Gynecology.

Carbonic anhydrases are involved in mitochondrial biogenesis and control the production of lactate by human Sertoli cells

The process that allows cells to control their pH and bicarbonate levels is essential for ionic and metabolic equilibrium. Carbonic anhydrases (CAs) catalyse the conversion of CO₂ to HCO 3 - and H⁺ and are thus essential for this process. Herein, we inhibited CAs with acetazolamide - ACT and SLC-0111 - to study their involvement in the metabolism, mitochondrial potential, mitochondrial biogenesis and lipid metabolism of human Sertoli cells (hSCs), obtained from biopsies from men with conserved spermatogenesis. We were able to identify three isoforms of CAs, one mitochondrial isoform (CA VB) and two cell membrane-bound isoforms (CA IX and CA XII) in hSCs. When assessing the expression of markers for mitochondrial biogenesis, we observed a decrease in HIF-1α, SIRT1, PGC1α and NRF-1 mRNAs after all CAs were inhibited, resulting in decreased mitochondrial DNA copy numbers. This was followed by an increased production of lactate and alanine in the same conditions. In addition, consumption of glucose was maintained after inhibition of all CAs in hSCs. These results indicate a reduced conversion of pyruvate to acetyl-coA, possibly due to decreased mitochondrial function, caused by CA inhibition in hSCs. Inhibition of CAs also caused alterations in lipid metabolism, since we detected an increased expression of hormone-sensitive lipase (HSL) in hSCs. Our results suggest that CAs are essential for mitochondrial biogenesis, glucose and lipid metabolism in hSCs. This is the first report showing that CAs play an essential role in hSC metabolic dynamics, being involved in mitochondrial biogenesis and controlling lactate production.

Carbonic anhydrase enzymes: Likely targets for inhalational anesthetics

Inhalational anesthetics such as isoflurane, desflurane and halothane are the mainstay medications for surgical procedures; upon inhalation, they produce anesthesia described as reversible unconsciousness with the features of amnesia, sleep, immobility and analgesia. To date, how they produce anesthesia is unknown. This study proposes that carbonic anhydrase enzymes are likely targets mediating the actions of inhalational anesthetics. Carbonic anhydrase enzymes, commonly expressed in living organisms, utilize carbon dioxide (CO₂) as a substrate and can generate H⁺ and HCO₃^- from CO₂ with a great efficiency. There are remarkable lines of evidence for their likely roles in mediating anesthetic actions. Firstly, carbonic anhydrase enzymes are extensively expressed in the brain and spinal cord, and their importance in the brain activity, especially for the GABA and NMDA receptor signaling pathways, has been demonstrated in numerous studies. According to these studies, they provide HCO₃^- for GABA-A receptor activities and also buffer HCO₃^- excess resulting from NMDA receptor activation. Activation of GABA-A and inhibition of NMDA receptors are associated with the induction of anesthesia by the intravenous general anesthetics propofol and ketamine, respectively. Secondly, the carbonic anhydrase inhibitors topiramate and zonisamide are effectively used in the treatment of epilepsy for decades; their chronic use results in the requirement of increased levels of amobarbital in order to produce anesthesia in the epileptic patients during WADA test. In addition, given that CO₂ is a substrate for these enzymes, their tertiary structure is likely has a hydrophobic pocket suitable for the anesthetic molecules to bind. Inhalational anesthetic molecules, which are lipophilic and inert in nature, have an ability to cross the membranes and inhibit carbonic anhydrases, which might not be accessible by topiramate and zonisamide. Unlike carbonic anhydrase inhibitors, they could bind to the hydrophobic pocket for CO₂ molecules and produce a profound effect called anesthesia. Finally, there is a great deal of similarities between the physiological actions of inhalational anesthetics and carbonic anhydrase inhibitors; moreover well-known side effects of inhalational anesthetics could be associated with the inhibition of carbonic anhydrases. Therefore, this article presents a hypothesis that the anesthetic actions of inhalational anesthetics could be due to their inhibitory effects on the carbonic anhydrases. Investigating this hypothesis might lead to the development of new safer anesthetics, and more importantly it might reveal an endogenous anesthetic pathway, in which the carbonic anhydrase system is a component along with the GABA-A and NMDA receptor systems.

Effects of low-level inhalation exposure to carbon dioxide in indoor environments: A short review on human health and psychomotor performance

Scientific literature and documents pertaining to the effects of inhalation exposure to carbon dioxide (CO₂) on human health and psychomotor performance were reviewed. Linear physiological changes in circulatory, cardiovascular, and autonomic systems on exposure to CO₂ at concentrations ranging from 500 to 5000 ppm were evident. Human experimental studies have suggested that short-term CO₂ exposure beginning at 1000 ppm affects cognitive performances including decision making and problem resolution. Changes in autonomic systems due to low-level exposure to CO₂ may involve these effects. Further research on the long-term effects of low-level CO₂ exposure on the autonomic system is required. Numerous epidemiological studies indicate an association between low-level exposure to CO₂ beginning at 700 ppm and building-related symptoms. Respiratory symptoms have been indicated in children exposed to indoor CO₂ concentrations higher than 1000 ppm. However, other indoor comorbid pollutants are possibly involved in such effects. In the context of significant linear increase of globally ambient CO₂ concentration caused by anthropogenic activities and sources, reducing indoor CO₂ levels by ventilation with ambient air represents an increase in energy consumption in an air-conditioned building. For the efficient energy control of CO₂ intruding a building from ambient air, the rise of atmospheric CO₂ concentration needs to be urgently suppressed.

Immobilization of Carbonic Anhydrase in Glass Micropipettes and Glass Fiber Filters for Flow-Through Reactor Applications

There are various ways of immobilizing carbonic anhydrase (CA) on solid materials. One of the final aims is to apply immobilized CA for the catalytic hydration of carbon dioxide (CO₂) as a first step in the conversion of gaseous CO₂ into solid products. The immobilization method investigated allows a straightforward, stable, and quantifiable immobilization of bovine erythrocyte carbonic anhydrase (BCA) on silicate surfaces. The method is based on the use of a water-soluble, polycationic second-generation dendronized polymer with on average 1000 repeating units, abbreviated as de-PG2₁₀₀₀. Several copies of BCA were first covalently linked to de-PG2₁₀₀₀ through stable bisaryl hydrazone (BAH) bonds. Then, the de-PG2₁₀₀₀-BAH-BCA conjugates obtained were adsorbed noncovalently either on microscopy glass coverslips, inside glass micropipettes, or in porous glass fiber filters. The apparent density of the immobilized BCA on the glass surfaces was about 8-10 pmol/cm². In all three cases, the immobilized enzyme was highly active and stable when tested with p-nitrophenyl acetate as a model enzyme substrate at room temperature. The micropipettes and the glass fiber filters were applied as flow-through systems for continuous operation at room temperature. In the case of the glass fiber filters, the filters were placed inside a homemade flow-through filter holder which allows flow-through runs with more than one filter connected in series. This offers the opportunity of increasing the substrate conversion by increasing the number of BCA-containing filters.

Effect of acetazolamide and methazolamide on diaphragm and dorsiflexor fatigue: a randomized controlled trial

Acetazolamide, a carbonic anhydrase (CA) inhibitor used clinically and to prevent acute mountain sickness, worsens skeletal muscle fatigue in animals and humans. In animals, methazolamide, a methylated analog of acetazolamide and an equally potent CA inhibitor, reportedly exacerbates fatigue less than acetazolamide. Accordingly, we sought to determine, in humans, if methazolamide would attenuate diaphragm and dorsiflexor fatigue compared with acetazolamide. Healthy men (dorsiflexor: n = 12; diaphragm: n = 7) performed fatiguing exercise on three occasions, after ingesting acetazolamide (250 mg three times a day) and then in random order, methazolamide (100 mg twice a day) or placebo for 48 h. For both muscles, subjects exercised at a fixed intensity until exhaustion on acetazolamide, with subsequent iso-time and -workload trials. Diaphragm exercise was performed using a threshold-loading device, while dorsiflexor exercise was isometric. Neuromuscular function was determined pre- and postexercise by potentiated transdiaphragmatic twitch pressure and dorsiflexor torque in response to stimulation of the phrenic and fibular nerve, respectively. Diaphragm contractility 3-10 min postexercise was impaired more for acetazolamide than methazolamide or placebo (82 ± 10, 87 ± 9, and 91 ± 8% of pre-exercise value; P < 0.05). Similarly, dorsiflexor fatigue was greater for acetazolamide than methazolamide (mean twitch torque of 61 ± 11 vs. 57 ± 13% of baseline, P < 0.05). In normoxia, methazolamide leads to less neuromuscular fatigue than acetazolamide, indicating a possible benefit for clinical use or in the prophylaxis of acute mountain sickness. NEW & NOTEWORTHY Acetazolamide, a carbonic anhydrase inhibitor, may worsen diaphragm and locomotor muscle fatigue after exercise; whereas, in animals, methazolamide does not impair diaphragm function. Compared with both methazolamide and the placebo, acetazolamide significantly compromised dorsiflexor function at rest and after exhaustive exercise. Similarly, diaphragm function was most compromised on acetazolamide followed by methazolamide and placebo. Methazolamide may be preferable over acetazolamide for clinical use and altitude illness prophylaxis to avoid skeletal muscle dysfunction.

Mechanisms of acid-base regulation in peritoneal dialysis

Background

Peritoneal dialysis (PD) contributes to restore acid-base homeostasis in patients with end-stage renal disease. The transport pathways for buffers and carbon dioxide (CO2) across the peritoneal membrane remain poorly understood.

Methods

Combining well-established PD protocols, whole-body plethysmography and renal function studies in mice, we investigated molecular mechanisms of acid-base regulation in PD, including the potential role of the water channel aquaporin-1 (AQP1).

Results

After instillation in peritoneal cavity, the pH of acidic dialysis solutions increased within minutes to rapidly equilibrate with blood pH, whereas the neutral pH of biocompatible solutions remained constant. Predictions from the three-pore model of peritoneal transport suggested that local production of HCO3- accounts at least in part for the changes in intraperitoneal pH observed with acidic solutions. Carbonic anhydrase (CA) isoforms were evidenced in the peritoneal membrane and their inhibition with acetazolamide significantly decreased local production of HCO3- and delayed changes in intraperitoneal pH. On the contrary, genetic deletion of AQP1 had no effect on peritoneal transport of buffers and diffusion of CO2. Besides intraperitoneal modifications, the use of acidic dialysis solutions enhanced acid excretion both at pulmonary and renal levels.

Conclusions

These findings suggest that changes in intraperitoneal pH during PD are mediated by bidirectional buffer transport and by CA-mediated production of HCO3- in the membrane. The use of acidic solutions enhances acid excretion through respiratory and renal responses, which should be considered in patients with renal failure.

An Update on the Metabolic Roles of Carbonic Anhydrases in the Model Alga Chlamydomonas reinhardtii

Carbonic anhydrases (CAs) are metalloenzymes that are omnipresent in nature. CAs catalyze the basic reaction of the reversible hydration of CO₂ to HCO₃⁻ and H⁺ in all living organisms. Photosynthetic organisms contain six evolutionarily different classes of CAs, which are namely: α-CAs, β-CAs, γ-CAs, δ-CAs, ζ-CAs, and θ-CAs. Many of the photosynthetic organisms contain multiple isoforms of each CA family. The model alga Chlamydomonas reinhardtii contains 15 CAs belonging to three different CA gene families. Of these 15 CAs, three belong to the α-CA gene family; nine belong to the β-CA gene family; and three belong to the γ-CA gene family. The multiple copies of the CAs in each gene family may be due to gene duplications within the particular CA gene family. The CAs of Chlamydomonas reinhardtii are localized in different subcellular compartments of this unicellular alga. The presence of a large number of CAs and their diverse subcellular localization within a single cell suggests the importance of these enzymes in the metabolic and biochemical roles they perform in this unicellular alga. In the present review, we update the information on the molecular biology of all 15 CAs and their metabolic and biochemical roles in Chlamydomonas reinhardtii. We also present a hypothetical model showing the known functions of CAs and predicting the functions of CAs for which precise metabolic roles are yet to be discovered.

Physicochemical determinants of pH in pectoralis major of three strains of laying hens housed in conventional and furnished cages

1. Post-mortem decline in muscle pH has traditionally been attributed to glycogenolysis-induced lactate accumulation. However, muscle pH ([H⁺]) is controlled by complex physicochemical relationships encapsulated in the Stewart model of acid-base chemistry and is determined by three system-independent variables - strong ion difference ([SID]), total concentration of weak acids ([A_tot]) and partial pressure of CO₂ (PCO₂). 2. This study investigated these system-independent variables in post-mortem pectoralis major muscles of Shaver White, Lohmann Lite and Lohmann Brown laying hens housed in conventional cages (CC) or furnished cages (FC) and evaluated the model by comparing calculated [H⁺] with previously measured [H⁺] values. 3. The model accounted for 99.7% of the variation in muscle [H⁺]. Differences in [SID] accounted for most or all of the variations in [H⁺] between strains. Greater PCO₂ in FC was counteracted by greater sequestration of strong base cations. The results demonstrate the accuracy and utility of the Stewart model for investigating determinants of meat [H⁺]. 4. The housing differences identified in this study suggested that hens housed in FC have improved muscle function and overall health due to the increased opportunity for movement. These findings support past studies showing improved animal welfare for hens housed in FC compared to CC. Therefore, the Stewart model has been identified as an accurate method to assess changes in the muscle at a cellular level that affect meat quality that also detect differences in the welfare status of the research subjects.

Evaluation of the water quality of the upper reaches of the main Southern Brazil river (Iguaçu river) through in situ exposure of the native siluriform Rhamdia quelen in cages

Increase in industrial growth, urban and agricultural pollution, with consequent impacts on aquatic ecosystems are a major focus of research worldwide. Still, not many studies assess the impacts of contamination through in situ studies, using native species, also considering the influence of seasonality on their responses. This study aimed to evaluate the water quality of the basin of the Upper Iguaçu River, the main source of water supply to Curitiba, a major capital of Southern Brazil, and its Metropolitan area. Several biomarkers were evaluated after in situ exposure of the native catfish Rhamdia quelen inside cages for 7 days. Ten study sites were chosen along the basin, based on a diffuse gradient of contamination, corresponding to regions upstream, downstream, and within "great Curitiba". In each site, fish were exposed in Summer and Winter. The complex mixture of contaminants of this hydrographic basin generated mortality, and ion-, osmoregulatory and respiratory disturbances in the catfish as, for example, reduction of plasma osmolality and ionic concentrations, increased hematocrit levels and gill water content, altered branchial and renal activities of the enzyme carbonic anhydrase, as well as raised levels of plasma cortisol and glucose. Biomarkers were mostly altered in fish exposed in Great Curitiba and immediately downstream. There was a notable influence of season on the responses of the jundiá. A multivariate redundancy analysis revealed that the best environmental variables explained 30% of the variation in biomarkers after controlling for spatial autocorrelation. Thus, this approach and the chosen parameters can be satisfactorily used to evaluate contamination environments with complex mixtures of contaminants, in other urban basins as well.