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Chaves G, Jardin C, Derst C, Musset B. Voltage-Gated Proton Channels in the Tree of Life. Biomolecules 2023; 13:1035. [PMID: 37509071 PMCID: PMC10377628 DOI: 10.3390/biom13071035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2023] [Revised: 06/14/2023] [Accepted: 06/21/2023] [Indexed: 07/30/2023] Open
Abstract
With a single gene encoding HV1 channel, proton channel diversity is particularly low in mammals compared to other members of the superfamily of voltage-gated ion channels. Nonetheless, mammalian HV1 channels are expressed in many different tissues and cell types where they exert various functions. In the first part of this review, we regard novel aspects of the functional expression of HV1 channels in mammals by differentially comparing their involvement in (1) close conjunction with the NADPH oxidase complex responsible for the respiratory burst of phagocytes, and (2) in respiratory burst independent functions such as pH homeostasis or acid extrusion. In the second part, we dissect expression of HV channels within the eukaryotic tree of life, revealing the immense diversity of the channel in other phylae, such as mollusks or dinoflagellates, where several genes encoding HV channels can be found within a single species. In the last part, a comprehensive overview of the biophysical properties of a set of twenty different HV channels characterized electrophysiologically, from Mammalia to unicellular protists, is given.
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Affiliation(s)
- Gustavo Chaves
- Center of Physiology, Pathophysiology and Biophysics, The Nuremberg Location, Paracelsus Medical University, 90419 Nuremberg, Germany
| | - Christophe Jardin
- Center of Physiology, Pathophysiology and Biophysics, The Nuremberg Location, Paracelsus Medical University, 90419 Nuremberg, Germany
| | - Christian Derst
- Center of Physiology, Pathophysiology and Biophysics, The Nuremberg Location, Paracelsus Medical University, 90419 Nuremberg, Germany
| | - Boris Musset
- Center of Physiology, Pathophysiology and Biophysics, The Nuremberg Location, Paracelsus Medical University, 90419 Nuremberg, Germany
- Center of Physiology, Pathophysiology and Biophysics, The Salzburg Location, Paracelsus Medical University, 5020 Salzburg, Austria
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Tikhonova IV, Grinevich AA, Kosyakova NI, Safronova VG. The effect of high temperature on kinetics of reactive species generation in patients with type 2 diabetes. Free Radic Biol Med 2022; 192:235-245. [PMID: 36198342 DOI: 10.1016/j.freeradbiomed.2022.09.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/12/2022] [Revised: 09/26/2022] [Accepted: 09/29/2022] [Indexed: 11/19/2022]
Abstract
The excessive amount of reactive species under chronic inflammation, which are accompanied by an increase body temperature, lead to diabetic complications. Phagocyte NADPH oxidase is the key enzyme in these processes. The role of high temperature in its regulation in diabetes is not clear. The aim was to investigate the effect of high temperature on NADPH-oxidase-dependent generation of reactive species in diabetic patients. Chemiluminescent method was applied to assess respiratory burst kinetics initiated by opsonized zymosan in blood or phorbol ester in isolated granulocytes. Analyzing ROC curves, the main predictors and changes in stages of activation of NADPH oxidase were determined. Phosphoisoforms of p47phox and p67phox were quantified by immunoblotting. Response to opsonized zymosan was lower in all subjects at 40 °C vs 37 °C, its kinetic parameters (except Tmax) were higher in blood of patients vs controls. Response rate was the main significant predictor to distinguish groups of subjects at 40 °C indicating NADPH oxidase upregulation in diabetes. Ca2+-dependent generation of reactive species by cells increased in both groups at 40 °C vs 37 °C, kinetic parameters were higher in patients. Initial phospho-p47phox level was higher in patient cells vs ones in controls. It was increased by ionomycin, phorbol ester, or 40 °C in control cells and unchanged in patient ones. Phospho-p67phox level was unchangeable in intact cells of healthy donors and patients at both temperatures. Excessive amounts of reactive species in patient cells were the consequence of granulocyte priming due to p47phox phosphorylation. Thus, high temperature decreased phagocytosis- and enhanced Ca2+-dependent generation of reactive species making the differences between controls and patients less pronounced. The effect of temperature on the generation of reactive species in blood granulocytes is associated with activity of NADPH oxidase that can be a prospective therapeutic target for pathologies accompanied by inflammation including type 2 diabetes.
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Affiliation(s)
- Irina V Tikhonova
- Institute of Cell Biophysics of Russian Academy of Sciences, Institutskaya st., 3 Pushchino, 142290, Russia.
| | - Andrei A Grinevich
- Institute of Cell Biophysics of Russian Academy of Sciences, Institutskaya st., 3 Pushchino, 142290, Russia
| | - Ninel I Kosyakova
- Hospital of Pushchino Scientific Centre of Russian Academy of Sciences, Institutskaya st., 1 Pushchino, 142290, Russia
| | - Valentina G Safronova
- Institute of Cell Biophysics of Russian Academy of Sciences, Institutskaya st., 3 Pushchino, 142290, Russia
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Reactive Oxygen Species in the Reproductive System: Sources and Physiological Roles. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2022; 1358:9-40. [DOI: 10.1007/978-3-030-89340-8_2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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VDAC Gating Thermodynamics, but Not Gating Kinetics, Are Virtually Temperature Independent. Biophys J 2020; 119:2584-2592. [PMID: 33189678 DOI: 10.1016/j.bpj.2020.10.039] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Revised: 10/06/2020] [Accepted: 10/16/2020] [Indexed: 12/17/2022] Open
Abstract
The voltage-dependent anion channel (VDAC) is the most abundant protein in the mitochondrial outer membrane and an archetypical β-barrel channel. Here, we study the effects of temperature on VDAC channels reconstituted in planar lipid membranes at the single- and multichannel levels within the 20°C to 40°C range. The temperature dependence of conductance measured on a single channel in 1 M KCl shows an increase characterized by a 10°C temperature coefficient Q10 = 1.22 ± 0.02, which exceeds that of the bathing electrolyte solution conductivity, Q10 = 1.17 ± 0.01. The rates of voltage-induced channel transition between the open and closed states measured on multichannel membranes also show statistically significant increases, with temperatures that are consistent with activation energy barriers of ∼10 ± 3 kcal/mol. At the same time, the gating thermodynamics, as characterized by the gating charge and voltage of equipartitioning, does not display any measurable temperature dependence. The two parameters stay within 3.2 ± 0.2 elementary charges and 30 ± 2 mV, respectively. Thus, whereas the channel kinetics, specifically its conductance and rates of gating response to voltage steps, demonstrates a clear increase with temperature, the conformational voltage-dependent equilibria are virtually insensitive to temperature. These results, which may be a general feature of β-barrel channel gating, suggest either an entropy-driven gating mechanism or a role for enthalpy-entropy compensation.
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Sadri S, Tomar N, Yang C, Audi SH, Cowley AW, Dash RK. Mechanistic computational modeling of the kinetics and regulation of NADPH oxidase 2 assembly and activation facilitating superoxide production. Free Radic Res 2020; 54:695-721. [PMID: 33059489 DOI: 10.1080/10715762.2020.1836368] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Reactive oxygen species (ROS) play a crucial role in many physiological processes. However, ROS overproduction leads to oxidative stress, which plays a critical role in cell injury/death and the pathogenesis of many diseases. Members of NADPH oxidase (NOX) family, most of which are comprised of membrane and cytosolic components, are known to be the major nonmitochondrial sources of ROS in many cells. NOX2 is a widely-expressed and well-studied NOX family member, which is activated upon assembly of its membrane subunits gp91 phox and p22 phox with its cytosolic subunits p40 phox , p47 phox , p67 phox , and Rac, facilitating ROS production. NOX2 activation is also enhanced by GTP and inhibited by GDP. However, there remains a lack of a mechanistic, quantitative, and integrated understanding of the kinetics and regulation of the assembly of these subunits and their relative contributions toward NOX2 activation and ROS production. Toward this end, we have developed a mechanistic computational model, which incorporates a generalized random rapid equilibrium binding mechanism for NOX2 assembly and activation as well as regulations by GTP (activation), GDP (inhibition), and individual subunits enhancing the binding of other subunits (mutual binding enhancement). The resulting model replicates diverse published kinetic data, including subunit concentration-dependent NOX2 activation and ROS production, under different assay conditions, with appropriate estimates of the unknown model parameters. The model provides a mechanistic, quantitative, and integrated framework for investigating the critical roles of NOX2 subunits in NOX2 assembly and activation facilitating ROS production in a variety of physiological and pathophysiological conditions. However, there is also a need for better quantitative kinetic data based on current understanding of NOX2 assembly and activation in order to test and further develop this model.
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Affiliation(s)
- Shima Sadri
- Department of Biomedical Engineering, Medical College of Wisconsin, Milwaukee, WIS, USA
| | - Namrata Tomar
- Department of Biomedical Engineering, Medical College of Wisconsin, Milwaukee, WIS, USA
| | - Chun Yang
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WIS, USA
| | - Said H Audi
- Department of Biomedical Engineering, Marquette University, Milwaukee, WIS, USA
| | - Allen W Cowley
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WIS, USA
| | - Ranjan K Dash
- Department of Biomedical Engineering, Medical College of Wisconsin, Milwaukee, WIS, USA.,Department of Physiology, Medical College of Wisconsin, Milwaukee, WIS, USA
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Abstract
The superoxide (O2·-)-generating NADPH oxidase complex of phagocytes comprises a membrane-associated heterodimeric flavocytochrome, known as cytochrome b 558 (consisting of NOX2 and p22phox) and four cytosolic regulatory proteins, p47phox, p67phox, p40phox, and the small GTPase Rac. Under physiological conditions, in the resting phagocyte, O2·- generation is initiated by engagement of membrane receptors by a variety of stimuli, followed by signal transduction sequences leading to the translocation of the cytosolic components to the membrane and their association with the cytochrome, a process known as NADPH oxidase assembly. A consequent conformational change in NOX2 initiates the electron flow along a redox gradient, from NADPH to molecular oxygen (O2), leading to the one-electron reduction of O2 to O2·-. Historically, methodological difficulties in the study of the assembled complex derived from stimulated cells, due to its lack of stability, led to the design of "cell-free" systems (also known as "broken cells" or in vitro systems). In a major paradigm shift, the cell-free systems have as their starting point NADPH oxidase components derived from resting (unstimulated) phagocytes, or as in the predominant method at present, recombinant proteins representing the components of the NADPH oxidase complex. In cell-free systems, membrane receptor stimulation and the signal transduction sequence are absent, the accent being placed on the actual process of assembly, all of which takes place in vitro. Thus, a mixture of the individual components of the NADPH oxidase is exposed in vitro to an activating agent, the most common being anionic amphiphiles, resulting in the formation of a complex between cytochrome b 558 and the cytosolic components and O2·- generation in the presence of NADPH. Alternative activating pathways require posttranslational modification of oxidase components or modifying the phospholipid milieu surrounding cytochrome b 558. Activation is commonly quantified by measuring the primary product of the reaction, O2·-, trapped immediately after its generation by an appropriate acceptor in a kinetic assay, permitting the calculation of rates of O2·- production, but numerous variations exist, based on the assessment of reaction products or the consumption of substrates. Cell-free assays played a paramount role in the identification and characterization of the components of the NADPH oxidase complex, the performance of structure-function studies, the deciphering of the mechanisms of assembly, the search for inhibitory drugs, and the diagnosis of various forms of chronic granulomatous disease (CGD).
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Tomar N, Sadri S, Cowley AW, Yang C, Quryshi N, Pannala VR, Audi SH, Dash RK. A thermodynamically-constrained mathematical model for the kinetics and regulation of NADPH oxidase 2 complex-mediated electron transfer and superoxide production. Free Radic Biol Med 2019; 134:581-597. [PMID: 30769160 PMCID: PMC6588456 DOI: 10.1016/j.freeradbiomed.2019.02.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/23/2018] [Revised: 01/31/2019] [Accepted: 02/04/2019] [Indexed: 12/28/2022]
Abstract
Reactive oxygen species (ROS) play an important role in cell signaling, growth, and immunity. However, when produced in excess, they are toxic to the cell and lead to premature aging and a myriad of pathologies, including cardiovascular and renal diseases. A major source of ROS in many cells is the family of NADPH oxidase (NOX), comprising of membrane and cytosolic components. NOX2 is among the most widely expressed and well-studied NOX isoform. Although details on the NOX2 structure, its assembly and activation, and ROS production are well elucidated experimentally, there is a lack of a quantitative and integrative understanding of the kinetics of NOX2 complex, and the various factors such as pH, inhibitory drugs, and temperature that regulate the activity of this oxidase. To this end, we have developed here a thermodynamically-constrained mathematical model for the kinetics and regulation of NOX2 complex based on diverse published experimental data on the NOX2 complex function in cell-free and cell-based assay systems. The model incorporates (i) thermodynamics of electron transfer from NADPH to O2 through different redox centers of the NOX2 complex, (ii) dependence of the NOX2 complex activity upon pH and temperature variations, and (iii) distinct inhibitory effects of different drugs on the NOX2 complex activity. The model provides the first quantitative and integrated understanding of the kinetics and regulation of NOX2 complex, enabling simulation of diverse experimental data. The model also provides several novel insights into the NOX2 complex function, including alkaline pH-dependent inhibition of the NOX2 complex activity by its reaction product NADP+. The model provides a mechanistic framework for investigating the critical role of NOX2 complex in ROS production and its regulation of diverse cellular functions in health and disease. Specifically, the model enables examining the effects of specific targeting of various enzymatic sources of pathological ROS which could overcome the limitations of pharmacological efforts aimed at scavenging ROS which has resulted in poor outcomes of antioxidant therapies in clinical studies.
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Affiliation(s)
- Namrata Tomar
- Department of Biomedical Engineering, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Shima Sadri
- Department of Biomedical Engineering, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Allen W Cowley
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Chun Yang
- Department of Physiology, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Nabeel Quryshi
- Department of Biomedical Engineering, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Venkat R Pannala
- Department of Biomedical Engineering, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Said H Audi
- Department of Biomedical Engineering, Marquette University, Milwaukee, WI, 53223, USA; Department of Biomedical Engineering, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Ranjan K Dash
- Department of Biomedical Engineering, Medical College of Wisconsin, Milwaukee, WI, 53226, USA; Department of Physiology, Medical College of Wisconsin, Milwaukee, WI, 53226, USA; Department of Biomedical Engineering, Marquette University, Milwaukee, WI, 53223, USA.
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Kopalli SR, Cha KM, Hwang SY, Jeong MS, Kim SK. Korean Red Ginseng ( Panax ginseng Meyer) with enriched Rg3 ameliorates chronic intermittent heat stress-induced testicular damage in rats via multifunctional approach. J Ginseng Res 2019; 43:135-142. [PMID: 30662302 PMCID: PMC6323164 DOI: 10.1016/j.jgr.2018.06.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 06/01/2018] [Accepted: 06/15/2018] [Indexed: 01/06/2023] Open
Abstract
BACKGROUND Panax ginseng Meyer, known as Korean Red Ginseng (KRG), is one of the important age-old traditional herbs used in boosting libido and improving male fertility. In this study, the effects of Rg3-enriched KRG extract (KGC04P) on heat stress-induced testicular damage in experimental rats was evaluated. METHODS Male rats (Sprague-Dawley) were divided into four groups (n = 10): normal control (NC), heat-stressed control (HC), heat-stressed plus KGC04P-100 mg/kg (HK100), and heat-stressed plus KGC04P-200 mg/kg (HK200) groups. Starting 1 week prior to heat stress, animals were administered orally with KGC04P (100 and 200 mg/kg) mixed with a regular pellet diet and continued for 25 weeks. Heat stress was induced to HC, HK100, and HK200 groups by intermittently exposing the animals to high temperatures (32 ± 1°C, 2 h/day). After 6 months, animals were euthanized under general anesthesia with carbon dioxide and evaluated for various parameters in serum and testicular tissue by using Western blotting, biochemical kits, and reverse transcription-polymerase chain reaction. RESULTS Significant (p < 0.05) alterations in several parameters, such as body/organ weight, sperm kinematics, and lipid metabolism marker levels, in the serum and testis of rats were observed. Further, the expression of testicular antioxidant enzymes, inflammatory cytokines, sex hormonal receptors, and spermatogenesis-related genes were also affected significantly (p < 0.05) in the heat-stressed group. However, KGC04P prevented the heat stress-induced changes in rats significantly (p < 0.05) at both concentrations. CONCLUSION KGC04P attenuated heat stress-induced testicular damage by a multifunctional approach and can be developed as an excellent therapeutic agent for hyperthermia-mediated male infertility.
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Affiliation(s)
| | - Kyu-Min Cha
- Department of Biomedical Chemistry, College of Biomedical & Health Science, Konkuk University, Chungju, Republic of Korea
| | - Seock-Yeon Hwang
- Department of Biomedical Laboratory Science, College of Applied Science and Industry, Daejeon University, Daejeon, Republic of Korea
| | - Min-Sik Jeong
- Department of Biomedical Chemistry, College of Biomedical & Health Science, Konkuk University, Chungju, Republic of Korea
| | - Si-Kwan Kim
- Department of Biomedical Chemistry, College of Biomedical & Health Science, Konkuk University, Chungju, Republic of Korea
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Kumar N, Singh AK. Reactive oxygen species in seminal plasma as a cause of male infertility. J Gynecol Obstet Hum Reprod 2018; 47:565-572. [DOI: 10.1016/j.jogoh.2018.06.008] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2017] [Revised: 06/13/2018] [Accepted: 06/21/2018] [Indexed: 12/31/2022]
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Ratanayotha A, Kawai T, Higashijima SI, Okamura Y. Molecular and functional characterization of the voltage-gated proton channel in zebrafish neutrophils. Physiol Rep 2018; 5:5/15/e13345. [PMID: 28774948 PMCID: PMC5555884 DOI: 10.14814/phy2.13345] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 06/05/2017] [Accepted: 06/07/2017] [Indexed: 11/24/2022] Open
Abstract
Voltage‐gated proton channels (Hv1/VSOP) are expressed in various cells types, including phagocytes, and are involved in diverse physiological processes. Although hvcn1, the gene encoding Hv1, has been identified across a wide range of species, most of the knowledge about its physiological function and expression profile is limited to mammals. In this study, we investigated the basic properties of DrHv1, the Hv1 ortholog in zebrafish (Danio rerio) which is an excellent animal model owing to the transparency, as well as its functional expression in native cells. Electrophysiological analysis using a heterologous expression system confirmed the properties of a voltage‐gated proton channel are conserved in DrHv1 with differences in threshold and activation kinetics as compared to mouse (Mus musculus) Hv1 (mHv1). RT‐PCR analysis revealed that hvcn1 is expressed in zebrafish neutrophils, as is the case in mammals. Subsequent electrophysiological analysis confirmed the functional expression of DrHv1 in zebrafish neutrophils, which suggests Hv1 function in phagocytes is conserved among vertebrates. We also found that DrHv1 is comparatively resistant to extracellular Zn2+, which is a potent inhibitor of mammalian Hv1, and this phenomenon appears to reflect variation in the Zn2+‐coordinating residue (histidine) within the extracellular linker region in mammalian Hv1. Notably, the serum Zn2+ concentration is much higher in zebrafish than in mouse, raising the possibility that Zn2+ sensitivity was acquired in accordance with a change in the serum Zn2+ concentration. This study highlights the biological variation and importance of Hv1 in different animal species.
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Affiliation(s)
- Adisorn Ratanayotha
- Laboratory of Integrative Physiology, Department of Physiology, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan
| | - Takafumi Kawai
- Laboratory of Integrative Physiology, Department of Physiology, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan
| | - Shin-Ichi Higashijima
- Laboratory of Behavioral Neurobiology, Department of Biodesign Research, Okazaki Institute for Integrative Bioscience, Okazaki, Aichi, Japan
| | - Yasushi Okamura
- Laboratory of Integrative Physiology, Department of Physiology, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan
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Masoud R, Serfaty X, Erard M, Machillot P, Karimi G, Hudik E, Wien F, Baciou L, Houée-Levin C, Bizouarn T. Conversion of NOX2 into a constitutive enzyme in vitro and in living cells, after its binding with a chimera of the regulatory subunits. Free Radic Biol Med 2017; 113:470-477. [PMID: 29079525 DOI: 10.1016/j.freeradbiomed.2017.10.376] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Revised: 10/20/2017] [Accepted: 10/23/2017] [Indexed: 11/30/2022]
Abstract
During the phagocytosis of pathogens by phagocyte cells, the NADPH oxidase complex is activated to produce superoxide anion, a precursor of microbial oxidants. The activated NADPH oxidase complex from phagocytes consists in two transmembrane proteins (Nox2 and p22phox) and four cytosolic proteins (p40phox, p47phox, p67phox and Rac1-2). In the resting state of the cells, these proteins are dispersed in the cytosol, the membrane of granules and the plasma membrane. In order to synchronize the assembly of the cytosolic subunits on the membrane components of the oxidase, a fusion of the cytosolic proteins p47phox, p67phox and Rac1 named trimera was constructed. The trimera investigated in this paper is composed of the p47phox segment 1-286, the p67phox segment 1-212 and the mutated Rac1(Q61L). We demonstrate that the complex trimera-cyt b558 is functionally comparable to the one containing the separated subunits. Each of the subunits p47phox, p67phox and Rac1Q61L has kept its own activating property. The trimera is produced in an activated conformation as seen by circular dichroism. However, the presence of amphiphile is still necessary in a cell-free system to trigger superoxide anion production. The COS7gp91-p22 cells expressing the trimera produce continuously superoxide anion at high rate. This constitutive activity in cells can be of particular interest for understanding the NADPH oxidase functioning independently of signaling pathways.
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Affiliation(s)
- Rawand Masoud
- Laboratoire de Chimie Physique, UMR8000, Université Paris Sud, CNRS, Université Paris Saclay, 91405 Orsay, France
| | - Xavier Serfaty
- Laboratoire de Chimie Physique, UMR8000, Université Paris Sud, CNRS, Université Paris Saclay, 91405 Orsay, France
| | - Marie Erard
- Laboratoire de Chimie Physique, UMR8000, Université Paris Sud, CNRS, Université Paris Saclay, 91405 Orsay, France
| | - Paul Machillot
- Laboratoire de Chimie Physique, UMR8000, Université Paris Sud, CNRS, Université Paris Saclay, 91405 Orsay, France
| | - Gilda Karimi
- Laboratoire de Chimie Physique, UMR8000, Université Paris Sud, CNRS, Université Paris Saclay, 91405 Orsay, France
| | - Elodie Hudik
- Laboratoire de Chimie Physique, UMR8000, Université Paris Sud, CNRS, Université Paris Saclay, 91405 Orsay, France
| | - Frank Wien
- Synchrotron SOLEIL, campus Paris Saclay, Gif-sur-Yvette, France
| | - Laura Baciou
- Laboratoire de Chimie Physique, UMR8000, Université Paris Sud, CNRS, Université Paris Saclay, 91405 Orsay, France
| | - Chantal Houée-Levin
- Laboratoire de Chimie Physique, UMR8000, Université Paris Sud, CNRS, Université Paris Saclay, 91405 Orsay, France
| | - Tania Bizouarn
- Laboratoire de Chimie Physique, UMR8000, Université Paris Sud, CNRS, Université Paris Saclay, 91405 Orsay, France.
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DeCoursey TE. The intimate and controversial relationship between voltage-gated proton channels and the phagocyte NADPH oxidase. Immunol Rev 2017; 273:194-218. [PMID: 27558336 DOI: 10.1111/imr.12437] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
One of the most fascinating and exciting periods in my scientific career entailed dissecting the symbiotic relationship between two membrane transporters, the Nicotinamide adenine dinucleotide phosphate reduced form (NADPH) oxidase complex and voltage-gated proton channels (HV 1). By the time I entered this field, there had already been substantial progress toward understanding NADPH oxidase, but HV 1 were known only to a tiny handful of cognoscenti around the world. Having identified the first proton currents in mammalian cells in 1991, I needed to find a clear function for these molecules if the work was to become fundable. The then-recent discoveries of Henderson, Chappell, and colleagues in 1987-1988 that led them to hypothesize interactions of both molecules during the respiratory burst of phagocytes provided an excellent opportunity. In a nutshell, both transporters function by moving electrical charge across the membrane: NADPH oxidase moves electrons and HV 1 moves protons. The consequences of electrogenic NADPH oxidase activity on both membrane potential and pH strongly self-limit this enzyme. Fortunately, both consequences specifically activate HV 1, and HV 1 activity counteracts both consequences, a kind of yin-yang relationship. Notwithstanding a decade starting in 1995 when many believed the opposite, these are two separate molecules that function independently despite their being functionally interdependent in phagocytes. The relationship between NADPH oxidase and HV 1 has become a paradigm that somewhat surprisingly has now extended well beyond the phagocyte NADPH oxidase - an industrial strength producer of reactive oxygen species (ROS) - to myriad other cells that produce orders of magnitude less ROS for signaling purposes. These cells with their seven NADPH oxidase (NOX) isoforms provide a vast realm of mechanistic obscurity that will occupy future studies for years to come.
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Affiliation(s)
- Thomas E DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University, Chicago, IL, USA
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13
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Souabni H, Wien F, Bizouarn T, Houée-Levin C, Réfrégiers M, Baciou L. The physicochemical properties of membranes correlate with the NADPH oxidase activity. Biochim Biophys Acta Gen Subj 2016; 1861:3520-3530. [PMID: 27378459 DOI: 10.1016/j.bbagen.2016.06.028] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2016] [Revised: 05/25/2016] [Accepted: 06/28/2016] [Indexed: 01/01/2023]
Abstract
BACKGROUND Phagocytes kill ingested microbes by exposure to high concentrations of toxic reactive species generated by NADPH-oxidases. This membrane-bound electron-transferring enzyme is tightly regulated by cellular signaling cascades. So far, molecular and biophysical studies of the NADPH-oxidase were performed over limited temperature ranges, which weaken our understanding of immune response or inflammatory events. In this work, we have inspected the influence of temperature and lipid membrane properties on the NADPH-oxidase activity using a system free of cell complexity. METHODS We have extended the experimental conditions of the accepted model for NADPH-oxidase activity, the so-called cell-free assay, to a large temperature range (10-40°C) using different membrane compositions (subcellular compartments or liposomes). RESULTS A remarkable increase of superoxide production rate was observed with rising temperature. Synchrotron radiation circular dichroism data showed that this is not correlated with protein secondary structure changes. When lipid bilayers are in fluid phase, Arrhenius plots of the oxidase activity showed linear relationships with small activation energy (Ea), while when in solid phase, high Ea was found. The sterol content modulates kinetic and thermodynamic parameters. CONCLUSION High temperature promotes the rate of superoxide production. The key element of this enhancement is related to membrane properties such as thickness and viscosity and not to protein structural changes. Membrane viscosity that can be driven by sterols is a paramount parameter of Ea of NADPH oxidase activity. The membrane bilayer state modulated by its sterol content may be considered locally as an enzyme regulator. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.
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Affiliation(s)
- Hager Souabni
- Laboratoire de Chimie Physique UMR 8000, Univ. Paris-Sud, CNRS, Université Paris Saclay, 91405 Orsay Cedex, France
| | - Frank Wien
- Synchrotron SOLEIL, Campus Paris-Saclay, 91192 Gif-sur-Yvette Cedex, France
| | - Tania Bizouarn
- Laboratoire de Chimie Physique UMR 8000, Univ. Paris-Sud, CNRS, Université Paris Saclay, 91405 Orsay Cedex, France
| | - Chantal Houée-Levin
- Laboratoire de Chimie Physique UMR 8000, Univ. Paris-Sud, CNRS, Université Paris Saclay, 91405 Orsay Cedex, France
| | | | - Laura Baciou
- Laboratoire de Chimie Physique UMR 8000, Univ. Paris-Sud, CNRS, Université Paris Saclay, 91405 Orsay Cedex, France.
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14
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Cho CL, Esteves SC, Agarwal A. Novel insights into the pathophysiology of varicocele and its association with reactive oxygen species and sperm DNA fragmentation. Asian J Androl 2016; 18:186-93. [PMID: 26732105 PMCID: PMC4770484 DOI: 10.4103/1008-682x.170441] [Citation(s) in RCA: 141] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Varicocele has been associated with reduced male reproductive potential. With the advances in biomolecular techniques, it has been possible to better understand the mechanisms involved in testicular damage provoked by varicocele. Current evidence suggests the central role of reactive oxygen species (ROS) and the resultant oxidative stress (OS) in the pathogenesis of varicocele-associated male subfertility although the mechanisms have not yet been fully described and it is likely to be multifactorial. Excessive ROS is associated with sperm DNA fragmentation, which may mediate the clinical manifestation of poor sperm function and fertilization outcome related to varicocele. Testing of ROS/OS and DNA fragmentation has the potential to provide additional diagnostic and prognostic information compared to conventional semen analysis and may guide therapeutic management strategies in individual patient.
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Affiliation(s)
- Chak-Lam Cho
- Division of Urology, Department of Surgery, Kwong Wah Hospital, 25 Waterloo Road, Yau Ma Tei, Hong Kong
| | - Sandro C Esteves
- ANDROFERT, Center for Male Reproduction, Av. Dr. Heitor Penteado 1464, Campinas, SP 13075-460, Brazil
| | - Ashok Agarwal
- American Center for Reproductive Medicine, 10681 Carnegie Avenue, X-11, Cleveland, OH 44195, USA
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15
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Abstract
The past decade has seen increasing use of the patch-clamp technique on neutrophils and eosinophils. The main goal of these electrophysiological studies has been to elucidate the mechanisms underlying the phagocyte respiratory burst. NADPH oxidase activity, which defines the respiratory burst in granulocytes, is electrogenic because electrons from NADPH are transported across the cell membrane, where they reduce oxygen to form superoxide anion (O2 (-)). This passage of electrons comprises an electrical current that would rapidly depolarize the membrane if the charge movement were not balanced by proton efflux. The patch-clamp technique enables simultaneous recording of NADPH oxidase-generated electron current and H(+) flux through the closely related H(+) channel. Increasing evidence suggests that other ion channels may play crucial roles in degranulation, phagocytosis, and chemotaxis, highlighting the importance of electrophysiological studies to advance knowledge of granulocyte function. Several configurations of the patch-clamp technique exist. Each has advantages and limitations that are discussed here. Meaningful measurements of ion channels cannot be achieved without an understanding of their fundamental properties. We describe the types of measurements that are necessary to characterize a particular ion channel.
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16
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Fujiwara Y, Okamura Y. Temperature-sensitive gating of voltage-gated proton channels. CURRENT TOPICS IN MEMBRANES 2014; 74:259-92. [PMID: 25366240 DOI: 10.1016/b978-0-12-800181-3.00010-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The voltage-gated proton channel (Hv) mediates robust proton transport down the proton electrochemical gradient. Hv is mainly expressed in immune cells, including neutrophils and macrophages, the physiological functions of which are temperature sensitive. In those cells, Hv plays key roles in the regulation of reactive oxygen species production and pH homeostasis. Proton transport through Hv is regulated by both the membrane potential and the pH difference across the cell membrane. Earlier studies showed that the properties of Hv, including proton conductance and gating, are highly temperature dependent. Hv consists of a voltage sensor domain involved in both voltage sensing and proton permeation and a C-terminal coiled coil region. Although the channel's activities are innate to the protomers, normally two protomers assemble as a dimer via interaction between C-terminal coiled coils. We recently discovered that the coiled-coil region of Hv dissociates at around room temperature, and that subtle changes in the coiled-coil region affect temperature-sensitive gating. In this chapter, we describe the physiological functions and molecular mechanisms of Hv, focusing mainly on the structure and thermosensitive properties of Hv.
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Affiliation(s)
- Yuichiro Fujiwara
- Laboratory of Integrative Physiology, Graduate School of Medicine, Osaka University, Suita, Japan
| | - Yasushi Okamura
- Laboratory of Integrative Physiology, Graduate School of Medicine, Osaka University, Suita, Japan
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17
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DeCoursey TE. Voltage-gated proton channels: molecular biology, physiology, and pathophysiology of the H(V) family. Physiol Rev 2013; 93:599-652. [PMID: 23589829 PMCID: PMC3677779 DOI: 10.1152/physrev.00011.2012] [Citation(s) in RCA: 178] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Voltage-gated proton channels (H(V)) are unique, in part because the ion they conduct is unique. H(V) channels are perfectly selective for protons and have a very small unitary conductance, both arguably manifestations of the extremely low H(+) concentration in physiological solutions. They open with membrane depolarization, but their voltage dependence is strongly regulated by the pH gradient across the membrane (ΔpH), with the result that in most species they normally conduct only outward current. The H(V) channel protein is strikingly similar to the voltage-sensing domain (VSD, the first four membrane-spanning segments) of voltage-gated K(+) and Na(+) channels. In higher species, H(V) channels exist as dimers in which each protomer has its own conduction pathway, yet gating is cooperative. H(V) channels are phylogenetically diverse, distributed from humans to unicellular marine life, and perhaps even plants. Correspondingly, H(V) functions vary widely as well, from promoting calcification in coccolithophores and triggering bioluminescent flashes in dinoflagellates to facilitating killing bacteria, airway pH regulation, basophil histamine release, sperm maturation, and B lymphocyte responses in humans. Recent evidence that hH(V)1 may exacerbate breast cancer metastasis and cerebral damage from ischemic stroke highlights the rapidly expanding recognition of the clinical importance of hH(V)1.
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Affiliation(s)
- Thomas E DeCoursey
- Dept. of Molecular Biophysics and Physiology, Rush University Medical Center HOS-036, 1750 West Harrison, Chicago, IL 60612, USA.
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18
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Agarwal A, Hamada A, Esteves SC. Insight into oxidative stress in varicocele-associated male infertility: part 1. Nat Rev Urol 2012; 9:678-90. [PMID: 23165403 DOI: 10.1038/nrurol.2012.197] [Citation(s) in RCA: 188] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Varicocele is recognized as the leading cause of male infertility because it can impair spermatogenesis through several distinct pathophysiological mechanisms. Current evidence supports oxidative stress as a key element in the pathophysiology of varicocele-related infertility, although these mechanisms have not yet been fully described. Measurement of the reactive oxygen species and other markers of oxidative stress, including the levels of the antioxidant enzymes catalase and superoxide dismutase, can provide valuable information on the extent of oxidative stress and might guide therapeutic management strategies. The testis can respond to varicocele-associated cell stressors, such as heat stress, ischaemia or production of vasodilators (for example, nitric oxide) at the expense of the generation of excessive reactive oxygen species. These responses have their own implications in exacerbating the underlying oxidative stress and on the subsequent infertility.
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Affiliation(s)
- Ashok Agarwal
- Center for Reproductive Medicine, Glickman Urological and Kidney Institute, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195, USA.
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19
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20
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Musset B, Cherny VV, DeCoursey TE. Strong glucose dependence of electron current in human monocytes. Am J Physiol Cell Physiol 2011; 302:C286-95. [PMID: 22012327 DOI: 10.1152/ajpcell.00335.2011] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Reactive oxygen species (ROS) production by human monocytes differs profoundly from that by neutrophils and eosinophils in its dependence on external media glucose. Activated granulocytes produce vast amounts of ROS, even in the absence of glucose. Human peripheral blood monocytes (PBM), in contrast, are suspected not to be able to produce any ROS if glucose is absent from the media. Here we compare ROS production by monocytes and neutrophils, measured electrophysiologically on a single-cell level. Perforated-patch-clamp measurements revealed that electron current appeared after stimulation of PBM with phorbol myristate acetate. Electron current reflects the translocation of electrons through the NADPH oxidase, the main source of ROS production. The electron current was nearly abolished by omitting glucose from the media. Furthermore, in preactivated glucose-deprived cells, electron current appeared immediately with the addition of glucose to the bath. To characterize glucose dependence of PBM further, NADPH oxidase activity was assessed as hydrogen peroxide (H(2)O(2)) production and was recorded fluorometrically. H(2)O(2) production exhibited similar glucose dependence as did electron current. We show fundamental differences in the glucose dependence of ROS in human monocytes compared with human neutrophils.
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Affiliation(s)
- Boris Musset
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, Illinois 60612, USA
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21
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Bahniwal M, Villanueva EB, Klegeris A. Moderate increase in temperature may exacerbate neuroinflammatory processes in the brain: human cell culture studies. J Neuroimmunol 2010; 233:65-72. [PMID: 21185608 DOI: 10.1016/j.jneuroim.2010.11.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2010] [Revised: 11/29/2010] [Accepted: 11/29/2010] [Indexed: 11/29/2022]
Abstract
The effect of a moderate, physiologically relevant rise in temperature on several neuroinflammatory parameters was investigated in vitro using human cell lines and cultured human astrocytes. A two degree Celsius rise in temperature was found to enhance the neurotoxicity of microglia-like and astrocytic cells, increase the release of monocyte chemotactic protein (MCP)-1 by activated human monocytic THP-1 cells and amplify the generation of reactive oxygen intermediates by differentiated HL-60 myelocytic cells. Moderate increases in body temperature may exacerbate neuroinflammation and neuronal injury in chronic neurodegenerative disorders. Hence, therapies aimed at lowering the body temperature could be used to slow down the progression of such diseases.
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Affiliation(s)
- Manpreet Bahniwal
- Department of Biology, University of British Columbia Okanagan, Kelowna, BC, Canada
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22
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Averaimo S, Milton RH, Duchen MR, Mazzanti M. Chloride intracellular channel 1 (CLIC1): Sensor and effector during oxidative stress. FEBS Lett 2010; 584:2076-84. [PMID: 20385134 DOI: 10.1016/j.febslet.2010.02.073] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2009] [Revised: 01/28/2010] [Accepted: 02/01/2010] [Indexed: 01/24/2023]
Abstract
Oxidative stress, characterized by overproduction of reactive oxygen species (ROS), is a major feature of several pathological states. Indeed, many cancers and neurodegenerative diseases are accompanied by altered redox balance, which results from dysregulation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. In this review, we consider the role of the intracellular chloride channel 1 (CLIC1) in microglial cells during oxidative stress. Following microglial activation, CLIC1 translocates from the cytosol to the plasma membrane where it promotes a chloride conductance. The resultant anionic current balances the excess charge extruded by the active NADPH oxidase, supporting the generation of superoxide by the enzyme. In this scenario, CLIC1 could be considered to act as both a second messenger and an executor.
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Affiliation(s)
- Stefania Averaimo
- Dipartimento di Scienze Biomolecolari e Biotecnologie, Università di Milano, Via Celoria 26, 20133 Milan, Italy.
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23
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DeCoursey TE. Voltage-gated proton channels find their dream job managing the respiratory burst in phagocytes. Physiology (Bethesda) 2010; 25:27-40. [PMID: 20134026 PMCID: PMC3023998 DOI: 10.1152/physiol.00039.2009] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The voltage-gated proton channel bears surprising resemblance to the voltage-sensing domain (S1-S4) of other voltage-gated ion channels but is a dimer with two conduction pathways. The proton channel seems designed for efficient proton extrusion from cells. In phagocytes, it facilitates the production of reactive oxygen species by NADPH oxidase.
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Affiliation(s)
- Thomas E DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, Illinois, USA.
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24
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Musset B, Capasso M, Cherny VV, Morgan D, Bhamrah M, Dyer MJS, DeCoursey TE. Identification of Thr29 as a critical phosphorylation site that activates the human proton channel Hvcn1 in leukocytes. J Biol Chem 2009; 285:5117-21. [PMID: 20037153 DOI: 10.1074/jbc.c109.082727] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Voltage-gated proton channels and NADPH oxidase function cooperatively in phagocytes during the respiratory burst, when reactive oxygen species are produced to kill microbial invaders. Agents that activate NADPH oxidase also enhance proton channel gating profoundly, facilitating its roles in charge compensation and pH(i) regulation. The "enhanced gating mode" appears to reflect protein kinase C (PKC) phosphorylation. Here we examine two candidates for PKC-delta phosphorylation sites in the human voltage-gated proton channel, H(V)1 (Hvcn1), Thr(29) and Ser(97), both in the intracellular N terminus. Channel phosphorylation was reduced in single mutants S97A or T29A, and further in the double mutant T29A/S97A, by an in vitro kinase assay with PKC-delta. Enhanced gating was evaluated by expressing wild-type (WT) or mutant H(V)1 channels in LK35.2 cells, a B cell hybridoma. Stimulation by phorbol myristate acetate enhanced WT channel gating, and this effect was reversed by treatment with the PKC inhibitor GF109203X. The single mutant T29A or double mutant T29A/S97A failed to respond to phorbol myristate acetate or GF109203X. In contrast, the S97A mutant responded like cells transfected with WT H(V)1. We conclude that under these conditions, direct phosphorylation of the proton channel molecule at Thr(29) is primarily responsible for the enhancement of proton channel gating. This phosphorylation is crucial to activation of the proton conductance during the respiratory burst in phagocytes.
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Affiliation(s)
- Boris Musset
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, Illinois 60612, USA
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25
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Kuno M, Ando H, Morihata H, Sakai H, Mori H, Sawada M, Oiki S. Temperature dependence of proton permeation through a voltage-gated proton channel. ACTA ACUST UNITED AC 2009; 134:191-205. [PMID: 19720960 PMCID: PMC2740922 DOI: 10.1085/jgp.200910213] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Voltage-gated proton channels are found in many different types of cells, where they facilitate proton movement through the membrane. The mechanism of proton permeation through the channel is an issue of long-term interest, but it remains an open question. To address this issue, we examined the temperature dependence of proton permeation. Under whole cell recordings, rapid temperature changes within a few milliseconds were imposed. This method allowed for the measurement of current amplitudes immediately before and after a temperature jump, from which the ratios of these currents (Iratio) were determined. The use of Iratio for evaluating the temperature dependence minimized the contributions of factors other than permeation. Temperature jumps of various degrees (DeltaT, -15 to 15 degrees C) were applied over a wide temperature range (4-49 degrees C), and the Q10s for the proton currents were evaluated from the Iratios. Q10 exhibited a high temperature dependence, varying from 2.2 at 10 degrees C to 1.3 at 40 degrees C. This implies that processes with different temperature dependencies underlie the observed Q10. A novel resistivity pulse method revealed that the access resistance with its low temperature dependence predominated in high temperature ranges. The measured temperature dependence of Q10 was decomposed into Q10 of the channel and of the access resistances. Finally, the Q10 for proton permeation through the voltage-gated proton channel itself was calculated and found to vary from 2.8 at 5 degrees C to 2.2 at 45 degrees C, as expected for an activation enthalpy of 64 kJ/mol. The thermodynamic features for proton permeation through proton-selective channels were discussed for the underlying mechanism.
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Affiliation(s)
- Miyuki Kuno
- Department of Physiology, Osaka City University Graduate School of Medicine, Abeno-ku, Osaka 545-8585, Japan
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26
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De Simoni A, Allen NJ, Attwell D. Charge compensation for NADPH oxidase activity in microglia in rat brain slices does not involve a proton current. Eur J Neurosci 2008; 28:1146-56. [PMID: 18783372 PMCID: PMC2628425 DOI: 10.1111/j.1460-9568.2008.06417.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2008] [Revised: 07/04/2008] [Accepted: 07/20/2008] [Indexed: 11/28/2022]
Abstract
The membrane properties of isolated cultured microglia have been extensively studied but it is important to understand their properties in situ, where they protect the brain against infection, but also contribute to neurodegenerative diseases. Microglia and macrophages attack bacteria by generating reactive oxygen species, a process which involves NADPH oxidase pumping electrons out across the cell membrane. The resulting inward current evokes a depolarization, which would inhibit the activity of the NADPH oxidase if there were no charge-compensating current which moves positive charge out across the membrane. The mechanism of this charge compensation is controversial. In neutrophils and in cultured microglia a depolarization-activated H(+) conductance has been proposed to provide charge compensation, and also to remove protons generated intracellularly by the NADPH oxidase. Alternatively, a depolarization-activated K(+) conductance has been proposed to mediate charge compensation. Here we show that in microglia, either in the resting state or when activated by the bacterial coat component lipopolysaccharide, both in acute and in cultured hippocampal slices, no significant H(+) current is detectable. This implies that the membrane properties of microglia in their normal cellular environment differ from those of cultured microglia (similarly, microglia generated a current in response to ATP but, unlike in culture, not to glutamate or GABA). Furthermore, the K(+) current (Kv1.3) that is activated by lipopolysaccharide is inactivated by depolarization, making it unsuitable for mediating charge compensation on a long time scale at positive voltages. Instead, charge compensation may be mediated by a previously undescribed non-selective cation current.
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Affiliation(s)
- Anna De Simoni
- Department of Physiology, University College London, London, UK
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27
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Abstract
The history of research on voltage-gated proton channels is recounted, from their proposed existence in dinoflagellates by Hastings in 1972 and their demonstration in snail neurons by Thomas and Meech in 1982 to the discovery in 2006 (after a decade of controversy) of genes that unequivocally code for proton channels. Voltage-gated proton channels are perfectly selective for protons, conduct deuterons half as well, and the conductance is strongly temperature dependent. These properties are consistent with a conduction mechanism involving hydrogen-bonded-chain transfer, in which the selectivity filter is a titratable amino acid residue. Channel opening is regulated stringently by pH such that only outward current is normally activated. Main functions of proton channels include acid extrusion from cells and charge compensation for the electrogenic activity of the phagocyte NADPH oxidase. Genetic approaches hold the promise of rapid progress in the near future.
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Affiliation(s)
- T E DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, 1750 W. Harrison, Chicago, Illinois 60612, USA.
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28
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A pH-stabilizing role of voltage-gated proton channels in IgE-mediated activation of human basophils. Proc Natl Acad Sci U S A 2008; 105:11020-5. [PMID: 18664579 DOI: 10.1073/pnas.0800886105] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Eosinophils and other phagocytes use NADPH oxidase to kill bacteria. Proton channels in human eosinophils and neutrophils are thought to sustain NADPH oxidase activity, and their opening is greatly enhanced by a variety of NADPH oxidase activators, including phorbol myristate acetate (PMA). In nonphagocytic cells that lack NADPH oxidase, no clear effect of PMA on proton channels has been reported. The basophil is a granulocyte that is developmentally closely related to the eosinophil but nevertheless does not express NADPH oxidase. Thus, one might expect that stimulating basophils with PMA would not affect proton currents. However, stimulation of human basophils in perforated-patch configuration with PMA, N-formyl-methionyl-leucyl-phenylalanine, or anti-IgE greatly enhanced proton currents, the latter suggesting involvement of proton channels during activation of basophils by allergens through their highly expressed IgE receptor (Fc epsilonRI). The anti-IgE-stimulated response occurred in a fraction of cells that varied among donors and was less profound than that to PMA. PKC inhibition reversed the activation of proton channels, and the proton channel response to anti-IgE or PMA persisted in Ca(2+)-free solutions. Zn(2+) at concentrations that inhibit proton current inhibited histamine release elicited by PMA or anti-IgE. Studied with confocal microscopy by using SNARF-AM and the shifted excitation and emission ratioing of fluorescence approach, anti-IgE produced acidification that was exacerbated in the presence of 100 microM Zn(2+). Evidently, proton channels are active in basophils during IgE-mediated responses and prevent excessive acidification, which may account for their role in histamine release.
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29
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Role of Nox2 in elimination of microorganisms. Semin Immunopathol 2008; 30:237-53. [PMID: 18574584 DOI: 10.1007/s00281-008-0126-3] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Accepted: 05/23/2008] [Indexed: 12/16/2022]
Abstract
NADPH oxidase of the phagocytic cells (Nox2) transfers electrons from cytosolic NADPH to molecular oxygen in the extracellular or intraphagosomal space. The produced superoxide anion (O*2) provides the source for formation of all toxic oxygen derivatives, but continuous O*2 generation depends on adequate charge compensation. The vital role of Nox2 in efficient elimination of microorganisms is clearly indicated by human pathology as insufficient activity of the enzyme results in severe, recurrent bacterial infections, the typical symptoms of chronic granulomatous disease. The goals of this contribution are to provide critical review of the Nox2-dependent cellular processes that potentially contribute to bacterial killing and degradation and to indicate possible targets of pharmacological interventions.
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30
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Morgan D, DeCoursey TE. Analysis of electrophysiological properties and responses of neutrophils. Methods Mol Biol 2008; 412:139-75. [PMID: 18453111 DOI: 10.1007/978-1-59745-467-4_11] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The past decade has seen increasing use of the patch clamp technique on neutrophils and eosinophils. The main goal of these electrophysiological studies has been to elucidate the mechanisms underlying the phagocyte respiratory burst. NADPH oxidase activity, which defines the respiratory burst in granulocytes, is electrogenic because electrons from NADPH are transported across the cell membrane, where they reduce oxygen to form superoxide anion (O2-). This passage of electrons comprises an electrical current that would rapidly depolarize the membrane if the charge movement were not balanced by proton efflux. The patch clamp technique enables simultaneous recording of NADPH oxidase-generated electron current and H+ flux through the closely related H+ channel. Increasing evidence suggests that other ion channels may play crucial roles in degranulation, phagocytosis, and chemotaxis, highlighting the importance of electrophysiological studies to advance knowledge of granulocyte function. Several configurations of the patch clamp technique exist. Each has advantages and limitations that are discussed here. Meaningful measurements of ion channels cannot be achieved without an understanding of their fundamental properties. We describe the types of measurements that are necessary to characterize a particular ion channel.
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Affiliation(s)
- Deri Morgan
- Department of Molecular Biophysics and Physiology, Rush University and Medical Center, Chicago, IL, USA
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31
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Characterisation of electron currents generated by the human neutrophil NADPH oxidase. Biochem Biophys Res Commun 2008; 368:656-61. [DOI: 10.1016/j.bbrc.2008.01.161] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2008] [Accepted: 01/26/2008] [Indexed: 11/22/2022]
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32
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Musset B, Cherny VV, Morgan D, Okamura Y, Ramsey IS, Clapham DE, DeCoursey TE. Detailed comparison of expressed and native voltage-gated proton channel currents. J Physiol 2008; 586:2477-86. [PMID: 18356202 DOI: 10.1113/jphysiol.2007.149427] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Two years ago, genes coding for voltage-gated proton channels in humans, mice and Ciona intestinalis were discovered. Transfection of cDNA encoding the human HVCN1 (H(V)1) or mouse (mVSOP) ortholog of HVCN1 into mammalian cells results in currents that are extremely similar to native proton currents, with a subtle, but functionally important, difference. Expressed proton channels exhibit high H(+) selectivity, voltage-dependent gating, strong temperature sensitivity, inhibition by Zn(2+), and gating kinetics similar to native proton currents. Like native channels, expressed proton channels are regulated by pH, with the proton conductance-voltage (g(H)-V) relationship shifting toward more negative voltages when pH(o) is increased or pH(i) is decreased. However, in every (unstimulated) cell studied to date, endogenous proton channels open only positive to the Nernst potential for protons, E(H). Consequently, only outward H(+) currents exist in the steady state. In contrast, when the human or mouse proton channel genes are expressed in HEK-293 or COS-7 cells, sustained inward H(+) currents can be elicited, especially with an inward proton gradient (pH(o) < pH(i)). Inward current is the result of a negative shift in the absolute voltage dependence of gating. The voltage dependence at any given pH(o) and pH(i) is shifted by about -30 mV compared with native H(+) channels. Expressed H(V)1 voltage dependence was insensitive to interventions that promote phosphorylation or dephosphorylation of native phagocyte proton channels, suggesting distinct regulation of expressed channels. Finally, we present additional evidence that speaks against a number of possible mechanisms for the anomalous voltage dependence of expressed H(+) channels.
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Affiliation(s)
- B Musset
- Department of Molecular Biophysics & Physiology, Rush University Medical Center, 1750 W. Harrison, Chicago, IL 60612, USA
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33
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Segal AW. The function of the NADPH oxidase of phagocytes and its relationship to other NOXs in plants, invertebrates, and mammals. Int J Biochem Cell Biol 2007; 40:604-18. [PMID: 18036868 PMCID: PMC2636181 DOI: 10.1016/j.biocel.2007.10.003] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2007] [Revised: 10/03/2007] [Accepted: 10/03/2007] [Indexed: 01/09/2023]
Abstract
The NADPH (nicotinamide adenine dinucleotide phosphate) oxidase (NOX) of ‘professional’ phagocytic cells transfers electrons across the wall of the phagocytic vacuole, forming superoxide in the lumen. It is generally accepted that this system promotes microbial killing through the generation of reactive oxygen species and through the activity of myeloperoxidase. An alternative scenario exists in which the passage of electrons across the membrane alters the pH and generates a charge that drives ions into, and out of, the vacuole. It is proposed that the primary function of the oxidase is to produce these pH changes and ion fluxes, and the issues surrounding these processes are considered. The neutrophil oxidase is the prototype of a whole family of NOXs that exist throughout biology, from plants to man, which might function, at least in part, in a similar fashion. Some examples of how these other NOXs might influence ion fluxes are examined.
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Affiliation(s)
- Anthony W Segal
- Centre for Molecular Medicine, University College London, 5 University Street, London WC1E 6JJ, UK.
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Morgan D, Cherny VV, Finnegan A, Bollinger J, Gelb MH, DeCoursey TE. Sustained activation of proton channels and NADPH oxidase in human eosinophils and murine granulocytes requires PKC but not cPLA2 alpha activity. J Physiol 2006; 579:327-44. [PMID: 17185330 PMCID: PMC2075394 DOI: 10.1113/jphysiol.2006.124248] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The prevailing hypothesis that a signalling pathway involving cPLA(2)alpha is required to enhance the gating of the voltage-gated proton channel associated with NADPH oxidase was tested in human eosinophils and murine granulocytes. This hypothesis invokes arachidonic acid (AA) liberated by cPLA(2)alpha as a final activator of proton channels. In human eosinophils studied in the perforated-patch configuration, phorbol myristate acetate (PMA) stimulation elicited NADPH oxidase-generated electron current (I(e)) and enhanced proton channel gating identically in the presence or absence of three specific cPLA(2)alpha inhibitors, Wyeth-1, pyrrolidine-2 and AACOCF(3) (arachidonyl trifluoromethyl ketone). In contrast, PKC inhibitors GFX (GF109203X) or staurosporine prevented the activation of either proton channels or NADPH oxidase. PKC inhibition during the respiratory burst reversed the activation of both molecules, suggesting that ongoing phosphorylation is required. This effect of GFX was inhibited by okadaic acid, implicating phosphatases in proton channel deactivation. Proton channel activation by AA was partially reversed by GFX or staurosporine, indicating that AA effects are due in part to activation of PKC. In granulocytes from mice with the cPLA(2)alpha gene disrupted (knockout mice), PMA or fMetLeuPhe activated NADPH oxidase and proton channels in a manner indistinguishable from the responses of control cells. Thus, cPLA(2)alpha is not essential to activate the proton conductance or for a normal respiratory burst. Instead, phosphorylation of the proton channel or an activating molecule converts the channel to its activated gating mode. The existing paradigm for regulation of the concerted activity of proton channels and NADPH oxidase must be revised.
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Affiliation(s)
- Deri Morgan
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, 1750 West Harrison, Chicago, IL 60612 USA
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Femling JK, Cherny VV, Morgan D, Rada B, Davis AP, Czirják G, Enyedi P, England SK, Moreland JG, Ligeti E, Nauseef WM, DeCoursey TE. The antibacterial activity of human neutrophils and eosinophils requires proton channels but not BK channels. J Gen Physiol 2006; 127:659-72. [PMID: 16702353 PMCID: PMC2151543 DOI: 10.1085/jgp.200609504] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2006] [Accepted: 04/25/2006] [Indexed: 02/01/2023] Open
Abstract
Electrophysiological events are of central importance during the phagocyte respiratory burst, because NADPH oxidase is electrogenic and voltage sensitive. We investigated the recent suggestion that large-conductance, calcium-activated K(+) (BK) channels, rather than proton channels, play an essential role in innate immunity (Ahluwalia, J., A. Tinker, L.H. Clapp, M.R. Duchen, A.Y. Abramov, S. Page, M. Nobles, and A.W. Segal. 2004. Nature. 427:853-858). In PMA-stimulated human neutrophils or eosinophils, we did not detect BK currents, and neither of the BK channel inhibitors iberiotoxin or paxilline nor DPI inhibited any component of outward current. BK inhibitors did not inhibit the killing of bacteria, nor did they affect NADPH oxidase-dependent degradation of bacterial phospholipids by extracellular gIIA-PLA(2) or the production of superoxide anion (O(2*)(-)). Moreover, an antibody against the BK channel did not detect immunoreactive protein in human neutrophils. A required role for voltage-gated proton channels is demonstrated by Zn(2+) inhibition of NADPH oxidase activity assessed by H(2)O(2) production, thus validating previous studies showing that Zn(2+) inhibited O(2*)(-) production when assessed by cytochrome c reduction. In conclusion, BK channels were not detected in human neutrophils or eosinophils, and BK inhibitors did not impair antimicrobial activity. In contrast, we present additional evidence that voltage-gated proton channels serve the essential role of charge compensation during the respiratory burst.
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Affiliation(s)
- Jon K Femling
- Inflammation Program, Roy J. and Luille A. Carver College of Medicine, University of Iowa, Coralville, 52241, USA
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Murphy R, DeCoursey TE. Charge compensation during the phagocyte respiratory burst. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2006; 1757:996-1011. [PMID: 16483534 DOI: 10.1016/j.bbabio.2006.01.005] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2005] [Revised: 01/04/2006] [Accepted: 01/11/2006] [Indexed: 11/25/2022]
Abstract
The phagocyte NADPH oxidase produces superoxide anion (O(2)(.-)) by the electrogenic process of moving electrons across the cell membrane. This charge translocation must be compensated to prevent self-inhibition by extreme membrane depolarization. Examination of the mechanisms of charge compensation reveals that these mechanisms perform several other vital functions beyond simply supporting oxidase activity. Voltage-gated proton channels compensate most of the charge translocated by the phagocyte NADPH oxidase in human neutrophils and eosinophils. Quantitative modeling of NADPH oxidase in the plasma membrane supports this conclusion and shows that if any other conductance is present, it must be miniscule. In addition to charge compensation, proton flux from the cytoplasm into the phagosome (a) helps prevent large pH excursions both in the cytoplasm and in the phagosome, (b) minimizes osmotic disturbances, and (c) provides essential substrate protons for the conversion of O(2)(*-) to H(2)O(2) and then to HOCl. A small contribution by K+ or Cl- fluxes may offset the acidity of granule contents to keep the phagosome pH near neutral, facilitating release of bactericidal enzymes. In summary, the mechanisms used by phagocytes for charge compensation during the respiratory burst would still be essential to phagocyte function, even if NADPH oxidase were not electrogenic.
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Affiliation(s)
- Ricardo Murphy
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL 60612, USA
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Obermeyer G, Tyerman SD. NH4+ currents across the peribacteroid membrane of soybean. Macroscopic and microscopic properties, inhibition by Mg2+, and temperature dependence indicate a SubpicoSiemens channel finely regulated by divalent cations. PLANT PHYSIOLOGY 2005; 139:1015-29. [PMID: 16183839 PMCID: PMC1256014 DOI: 10.1104/pp.105.066670] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2005] [Revised: 07/28/2005] [Accepted: 07/30/2005] [Indexed: 05/04/2023]
Abstract
The control of ammonium (NH(4)(+)) transport is critical in preventing futile cycles of NH(4)(+)/ammonia transport. An unusual nonselective cation channel with subpicoSiemens single-channel conductance permeable to NH(4)(+) had previously been identified in the peribacteroid membrane (PBM) of symbiosomes from soybean (Glycine max) nodules. Here, we investigate the proposed channel mechanism and its control by luminal magnesium. Currents carried by NH(4)(+) were measured in inside-out PBM patches by patch clamp. NH(4)(+) transport corresponding to the physiological direction of net transfer showed time-dependent activation and associated single-channel-like events. These could not be resolved to discrete conductances but had the same selectivity as the total current. The voltage dependence of the steady-state current was affected by temperature consistent with the rate constant of channel opening being reduced with decreased temperature. This resulted in steady-state currents that were more temperature sensitive at voltages where the current was only partially activated. When fully activated, the current reflected more the ion conduction through open channels and had an activation energy of 28.2 kJ mol(-1) (Q10 = 1.51, 8 degrees C-24 degrees C). Increased Mg(2+) on the symbiosome lumen side blocked the current (ID(50) = 351 microm, with 60 mm NH(4)(+)). Complete inhibition with 2 mm Mg(2+) was relieved with a small increase in NH(4)(+) on the lumen side of the membrane (shift of 60-70 mm). With Mg(2+) the selectivity of the transport for divalent cations increased. From these features, we propose a divalent-dependent feedback regulation of the PBM-nonselective cation channel that could maintain a constant NH(4)(+) gradient across the membrane.
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Affiliation(s)
- Gerhard Obermeyer
- Molecular Plant Physiology, Division of Allergy and Immunobiology, Department of Molecular Biology, University of Salzburg, Austria
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Morgan D, Cherny VV, Murphy R, Katz BZ, DeCoursey TE. The pH dependence of NADPH oxidase in human eosinophils. J Physiol 2005; 569:419-31. [PMID: 16195320 PMCID: PMC1464255 DOI: 10.1113/jphysiol.2005.094748] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
NADPH oxidase generates reactive oxygen species that are essential to innate immunity against microbes. Like most enzymes, it is sensitive to pH, although the relative importance of pH(o) and pH(i) has not been clearly distinguished. We have taken advantage of the electrogenic nature of NADPH oxidase to determine its pH dependence in patch-clamped individual human eosinophils using the electron current to indicate enzyme activity. Electron current stimulated by PMA (phorbol myristate acetate) was recorded in both perforated-patch configuration, using an NH4+ gradient to control pH(i), and in excised, inside-out patches of membrane. No electron current was detected in cells or excised patches from eosinophils from a patient with chronic granulomatous disease. When the pH was varied symmetrically (pH(o) = pH(i)) in cells in perforated-patch configuration, NADPH oxidase-generated electron current was maximal at pH 7.5, decreasing drastically at higher or lower values. Varying pH(o) and pH(i) independently revealed that this pH dependence was entirely due to effects of pH(i) and that the oxidase is insensitive to pH(o). Surprisingly, the electron current in inside-out patches of membrane was only weakly sensitive to pH(i), indicating that the enzyme turnover rate per se is not strongly pH dependent. The most likely interpretation is that assembly or deactivation of the NADPH oxidase complex has one or more pH-sensitive steps, and that pH-dependent changes in electron current in intact cells mainly reflect different numbers of active complexes at different pH.
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Affiliation(s)
- Deri Morgan
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, 1750 West Harrison, Chicago, IL 60612, USA
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Arbogast S, Reid MB. Oxidant activity in skeletal muscle fibers is influenced by temperature, CO2 level, and muscle-derived nitric oxide. Am J Physiol Regul Integr Comp Physiol 2004; 287:R698-705. [PMID: 15178539 DOI: 10.1152/ajpregu.00072.2004] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Free radicals are produced continuously by skeletal muscle fibers. Extracellular release of reactive oxygen species (ROS) and nitric oxide (NO) derivatives has been demonstrated, but little is known about intracellular oxidant regulation. We used a fluorescent oxidant probe, 2',7'-dichlorofluorescin (DCFH), to assess net oxidant activity in passive muscle fiber bundles isolated from mouse diaphragm and studied in vitro. We tested the following three hypotheses. 1) Net oxidant activity is decreased by muscle cooling. 2) CO(2) exposure depresses intracellular oxidant activity. 3) Muscle-derived ROS and NO both contribute to overall oxidant activity. Our results indicate that DCFH oxidation was diminished by cooling muscle fibers from 37 degrees C to 23 degrees C (P < 0.001). The rate of DCFH oxidation correlated positively with CO(2) exposure (0-10%; P < 0.05) and negatively with concurrent changes in pH (7.0-8.5; P < 0.05). Separate exposures to anti-ROS enzymes (superoxide dismutase, 1 kU/ml; catalase, 1 kU/ml), a glutathione peroxidase mimetic (ebselen, 30 microM), NO synthase inhibitors (N(omega)-nitro-l-arginine methyl ester, 1 mM; N(omega)-monomethyl-l-arginine, 1 mM), or an NO scavenger (hemoglobin, 1 microM) each inhibited DCFH oxidation (P < 0.05). Oxidation was increased by hydrogen peroxide, 100 microM, an NO donor (NOC-22, 400 microM), or the substrate for NO synthase (l-arginine, 5 mM). We conclude that net oxidant activity in resting muscle fibers is 1) decreased at subphysiological temperatures, 2) increased by CO(2) exposure, and 3) influenced by muscle-derived ROS and NO derivatives to similar degrees.
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Affiliation(s)
- Sandrine Arbogast
- Dept. of Physiology, Univ. of Kentucky, 800 Rose St., Rm. MS-509; Lexington, KY 40536-0298, USA
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DeCoursey TE. During the respiratory burst, do phagocytes need proton channels or potassium channels, or both? Sci Signal 2004; 2004:pe21. [PMID: 15150421 DOI: 10.1126/stke.2332004pe21] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The NADPH (reduced form of nicotinamide adenine dinucleotide phosphate) oxidase enzyme complex, a crucial component of innate immunity, produces superoxide anion (O2-), which is a precursor to many reactive oxygen species. NADPH oxidase produces O2- by transferring electrons from intracellular NADPH across the membrane to extracellular (or phagosomal) oxygen and is thus electrogenic. It is widely believed that electroneutrality is preserved by proton flux through voltage-gated proton channels. A series of recent papers have challenged several key aspects of this view of the "respiratory burst." The most recent study solidifies the proposal that O2- and other reactive oxygen species produced by phagocytes are not toxic to microbes under physiological conditions. Further, an essential role for high-conductance, Ca2+-activated K+ (maxi-K+) channels in microbe killing is proposed. Finally, the results cast doubt on the widely held view that H+ efflux through voltage-gated proton channels (i) is the main mechanism of charge compensation, and (ii) is essential to continuous O2- production by the NADPH oxidase. My analysis of the new data and of a large body of data in the literature indicates that the proposed role of maxi-K+ channels in the respiratory burst is not yet credibly established. H+ efflux through proton channels thus remains the most viable mechanism for charge compensation and continuous O2- production. The important question of the toxicity of reactive oxygen species in phagocytes and in other cells, which has long been simply taken for granted, is a widespread assumption that deserves critical study.
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Affiliation(s)
- Thomas E DeCoursey
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, 1750 West Harrison, Chicago, IL 60612, USA.
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