scholarly journals Channel-like slippage modes in the human anion/proton exchanger ClC-4

2009 ◽  
Vol 133 (5) ◽  
pp. 485-496 ◽  
Author(s):  
Alexi K. Alekov ◽  
Christoph Fahlke
Keyword(s):  
Mammalian Cells ◽  
Stable Distribution ◽  
Noise Analysis ◽  
Anion Channel ◽  
Proton Exchange ◽  
Anion Channels ◽  
Mode Behavior ◽  
Voltage Dependent ◽  
Transport Modes ◽  
Active Anion

The ClC family encompasses two classes of proteins with distinct transport functions: anion channels and transporters. ClC-type transporters usually mediate secondary active anion–proton exchange. However, under certain conditions they assume slippage mode behavior in which proton and anion transport are uncoupled, resulting in passive anion fluxes without associated proton movements. Here, we use patch clamp and intracellular pH recordings on transfected mammalian cells to characterize exchanger and slippage modes of human ClC-4, a member of the ClC transporter branch. We found that the two transport modes differ in transport mechanisms and transport rates. Nonstationary noise analysis revealed a unitary transport rate of 5 × 105 s−1 at +150 mV for the slippage mode, indicating that ClC-4 functions as channel in this mode. In the exchanger mode, unitary transport rates were 10-fold lower. Both ClC-4 transport modes exhibit voltage-dependent gating, indicating that there are active and non-active states for the exchanger as well as for the slippage mode. ClC-4 can assume both transport modes under all tested conditions, with exchanger/channel ratios determined by the external anion. We propose that binding of transported anions to non-active states causes transition from slippage into exchanger mode. Binding and unbinding of anions is very rapid, and slower transitions of liganded and non-liganded states into active conformations result in a stable distribution between the two transport modes. The proposed mechanism results in anion-dependent conversion of ClC-type exchanger into an anion channel with typical attributes of ClC anion channels.

scholarly journals Functional Properties of the Retinal Glutamate Transporters GLT-1c and EAAT5

2013 ◽  
Vol 289 (3) ◽  
pp. 1815-1824 ◽  
Author(s):  
Nicole Schneider ◽  
Sönke Cordeiro ◽  
Jan-Philipp Machtens ◽  
Simona Braams ◽  
Thomas Rauen ◽  
...  
Keyword(s):  
Functional Properties ◽  
Mammalian Cells ◽  
Single Channel ◽  
Excitatory Amino Acid ◽  
Noise Analysis ◽  
Anion Channel ◽  
Glutamate Transporters ◽  
Glutamate Transport ◽  
Anion Channels ◽  
Voltage Range

In the mammalian retina, glutamate uptake is mediated by members of a family of glutamate transporters known as “excitatory amino acid transporters (EAATs).” Here we cloned and functionally characterized two retinal EAATs from mouse, the GLT-1/EAAT2 splice variant GLT-1c, and EAAT5. EAATs are glutamate transporters and anion-selective ion channels, and we used heterologous expression in mammalian cells, patch-clamp recordings and noise analysis to study and compare glutamate transport and anion channel properties of both EAAT isoforms. We found GLT-1c to be an effective glutamate transporter with high affinity for Na+ and glutamate that resembles original GLT-1/EAAT2 in all tested functional aspects. EAAT5 exhibits glutamate transport rates too low to be accurately measured in our experimental system, with significantly lower affinities for Na+ and glutamate than GLT-1c. Non-stationary noise analysis demonstrated that GLT-1c and EAAT5 also differ in single-channel current amplitudes of associated anion channels. Unitary current amplitudes of EAAT5 anion channels turned out to be approximately twice as high as single-channel amplitudes of GLT-1c. Moreover, at negative potentials open probabilities of EAAT5 anion channels were much larger than for GLT-1c. Our data illustrate unique functional properties of EAAT5, being a low-affinity and low-capacity glutamate transport system, with an anion channel optimized for anion conduction in the negative voltage range.

scholarly journals Voltage-dependent block of endothelial volume-regulated anion channels by calix[4]arenes

1998 ◽  
Vol 275 (3) ◽  
pp. C646-C652 ◽  
Author(s):  
Guy Droogmans ◽  
Jean Prenen ◽  
Jan Eggermont ◽  
Thomas Voets ◽  
Bernd Nilius
Keyword(s):  
Open Channel ◽  
Single Channel ◽  
Anion Channel ◽  
Anion Channels ◽  
Channel Conductance ◽  
Open Channel Block ◽  
Maximum Inhibition ◽  
Voltage Dependent ◽  
A Site ◽  
Maximal Block

We have studied the effects of calix[4]arenes on the volume-regulated anion channel (VRAC) currents in cultured calf pulmonary artery endothelial cells. TS- and TS-TM-calix[4]arenes induced a fast inhibition at positive potentials but were ineffective at negative potentials. Maximal block occurred at potentials between 30 and 50 mV. Lowering extracellular pH enhanced the block and shifted the maximum inhibition to more negative potentials. Current inhibition was also accompanied by an increased current noise. From the analysis of the calix[4]arene-induced noise, we obtained a single-channel conductance of 9.3 ± 2.1 pS ( n = 9) at +30 mV. The voltage- and time-dependent block were described using a model in which calix[4]arenes bind to a site at an electrical distance of 0.25 inside the channel with an affinity of 220 μM at 0 mV. Binding occludes VRAC at moderately positive potentials, but calix[4]arenes permeate the channel at more positive potentials. In conclusion, our data suggest an open-channel block of VRAC by calix[4]arenes that also depends on the protonation of the binding site within the pore.

Endothelium modulates anion channel-dependent aortic contractions to iodide

2000 ◽  
Vol 278 (5) ◽  
pp. H1527-H1536 ◽  
Author(s):  
Fred S. Lamb ◽  
Thomas J. Barna
Keyword(s):  
Nitric Oxide ◽  
Smooth Muscle ◽  
Membrane Potential ◽  
Anion Channel ◽  
Anion Channels ◽  
Anion Substitution ◽  
Voltage Dependent ◽  
Voltage Dependent Calcium Channels ◽  
Channel Dependent ◽  
Cytochrome P 450

Anion currents contribute to vascular smooth muscle (VSM) membrane potential. The substitution of extracellular chloride (Cl) with iodide (I) or bromide (Br) initially inhibited and then potentiated isometric contractile responses of rat aortic rings to norepinephrine. Anion substitution alone produced a small relaxation, which occurred despite a lack of active tone and minimal subsequent contraction of endothelium-intact rings (4.2 ± 1.2% of the response to 90 mM KCl). Endothelium-denuded rings underwent a similar initial relaxation but then contracted vigorously (I > Br). Responses to 130 mM I (93.7 ± 1.9% of 90 mM KCl) were inhibited by nifedipine (10− 6 M), niflumic acid (10− 5 M), tamoxifen (10− 5 M), DIDS (10− 4 M), and[Formula: see text]-free buffer (HEPES 10 mM) but not by bumetanide (10− 5 M). Intact rings treated with N ω-nitro-l-arginine (10− 4 M) responded weakly to I (15.5 ± 2.1% of 90 mM KCl), whereas hemoglobin (10− 5 M), indomethacin (10− 6 M), 17-octadecynoic acid (10− 5 M), and 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (10− 6 M) all failed to augment the response of intact rings to I. We hypothesize that VSM takes up I primarily via an anion exchanger. Subsequent I efflux through anion channels having a selectivity of I > Br > Cl produces depolarization. In endothelium-denuded or agonist-stimulated vessels, this current is sufficient to activate voltage-dependent calcium channels and cause contraction. Neither nitric oxide nor prostaglandins are the primary endothelial modulator of these anion channels. If they are regulated by an endothelium-dependent hyperpolarizing factor it is not a cytochrome P-450 metabolite.

scholarly journals Depletion of a Toxoplasma porin leads to defects in mitochondrial morphology and contacts with the ER

2021 ◽  
Author(s):  
Natalia Mallo ◽  
Jana Ovciarikova ◽  
Erica S. Martins-Duarte ◽  
Stephan C. Baehr ◽  
Marco Biddau ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Protein Import ◽  
Morphological Changes ◽  
Anion Channel ◽  
Multiple Roles ◽  
Mitochondrial Morphology ◽  
Voltage Dependent Anion Channel ◽  
Voltage Dependent ◽  
Molecule Transport ◽  
Small Molecule Transport

The Voltage Dependent Anion channel (VDAC) is a ubiquitous channel in the outer membrane of the mitochondrion with multiple roles in protein, metabolite and small molecule transport. In mammalian cells, VDAC, as part of a larger complex including the inositol triphosphate receptor, has been shown to have a role in mediating contacts between the mitochondria and endoplasmic reticulum (ER). We identify VDAC of the pathogenic apicomplexan Toxoplasma gondii and demonstrate its importance for parasite growth. We show that VDAC is involved in protein import and metabolite transfer to mitochondria. Further, depletion of VDAC resulted in significant morphological changes of the mitochondrion and ER, suggesting a role in mediating contacts between these organelles in T. gondii.

scholarly journals Depletion of voltage-dependent anion channel (VDAC) of Toxoplasma gondii affects multiple mitochondrial functions, but not calcium signalling

2020 ◽  
Author(s):  
Natalia Mallo ◽  
Erica S. Martins Duarte ◽  
Stephan C. Baehr ◽  
Marco Biddau ◽  
Jana Ovciarikova ◽  
...  
Keyword(s):  
Toxoplasma Gondii ◽  
Mammalian Cells ◽  
Protein Import ◽  
Morphological Changes ◽  
Calcium Signalling ◽  
Anion Channel ◽  
Voltage Dependent Anion Channel ◽  
Mitochondrial Functions ◽  
Voltage Dependent ◽  
Molecule Transport

AbstractThe Voltage Dependent Anion channel (VDAC) is a ubiquitous channel in the outer membrane of the mitochondrion with multiple roles in protein, metabolite and small molecule transport. In mammalian cells, VDAC, as part of a larger complex including the inositol triphosphate receptor, has been shown to have a role in mediating contact between the mitochondria and ER. We identify VDAC of the pathogenic apicomplexan Toxoplasma gondii and demonstrate its importance for parasite growth. We show that VDAC is involved in protein import and metabolite transfer to the mitochondria, but does not appear to modulate calcium (Ca2+) signalling. Further, depletion of VDAC resulted in significant morphological changes of the mitochondrion and ER, suggesting a role in mediating contacts between these organelles in T. gondii.

scholarly journals Voltage-dependent anion channels mediated apoptosis in refractory epilepsy

Open Medicine ◽  
2020 ◽  
Vol 15 (1) ◽  
pp. 745-753
Author(s):  
Yan Zhao ◽  
Wen-Jing Jiang ◽  
Lin Ma ◽  
Yan Lin ◽  
Xing-Bang Wang
Keyword(s):  
Cell Death ◽  
Essential Role ◽  
Refractory Epilepsy ◽  
Apoptotic Cell ◽  
Anion Channel ◽  
Anion Channels ◽  
Voltage Dependent Anion Channel ◽  
Caspase 9 ◽  
Voltage Dependent

AbstractThe purpose of this study was to investigate the role of voltage-dependent anion channel (VDAC) in mitochondria-mediated apoptosis of neurons in refractory epilepsy. Western blot analyses were carried out to detect the changes in cytochrome C, caspase 9, Bax, and Bcl-2. TUNEL assays were also carried out to investigate cell apoptosis under the upregulation and downregulation of VDAC1 with or without Bax or Bcl-2. VDAC1 induced Bax, Bcl-2, and caspase 9, increasing the release of cytochrome C. VDAC1 played an essential role in the apoptotic cell death of refractory epilepsy. It is concluded that VDAC1 plays an important role in refractory epilepsy and could be a possible therapeutic target of anti-epileptic drugs. The current study provides a new understanding of the possible mechanisms of refractory epilepsy.

scholarly journals Expression of voltage-dependent anion channels in endometrial cancer and its potential prognostic significance

Tumor Biology ◽  
2020 ◽  
Vol 42 (8) ◽  
pp. 101042832095105
Author(s):  
Paweł Jóźwiak ◽  
Piotr Ciesielski ◽  
Ewa Forma ◽  
Karolina Kozal ◽  
Katarzyna Wójcik-Krowiranda ◽  
...  
Keyword(s):  
Overall Survival ◽  
Endometrial Cancer ◽  
Protein Level ◽  
Prognostic Significance ◽  
Anion Channel ◽  
Mrna Levels ◽  
Anion Channels ◽  
Voltage Dependent Anion Channel ◽  
Poor Overall Survival ◽  
Voltage Dependent

The exchange of metabolites between mitochondria and cytosol occurs through pores formed by voltage-dependent anion channel proteins. Voltage-dependent anion channels appear to be master regulators of mitochondrial bioenergetics and the intracellular flow of energy. Deregulation of voltage-dependent anion channels expression is thought to be related to mitochondrial dysfunction in cancer. The aim of this study was to investigate the mRNA and protein expression levels of VDAC1, VDAC2, and VDAC3 in relation to clinicopathological characteristics of endometrial cancer as well as the prognostic significance of voltage-dependent anion channels expression for overall survival. VDAC1 and VDAC3 expressions were significantly higher in cancer compared to normal tissues. Kaplan–Meier analysis indicated that high expression of all VDAC genes or high VDAC2 protein level predicted poor overall survival. Multivariate analysis identified the VDAC1 and VDAC2 mRNA levels as well as VDAC2 protein level as independent prognostic factors. Our results suggest that increased expression of voltage-dependent anion channels correlates with tumor progression and may serve as a potential prognostic biomarker in endometrial cancer.

scholarly journals Response of yeast to the regulated expression of proteins in the Bcl-2 family

2003 ◽  
Vol 374 (2) ◽  
pp. 393-402 ◽  
Author(s):  
Peter POLČIC ◽  
Michael FORTE
Keyword(s):  
Family Member ◽  
Mammalian Cells ◽  
Family Members ◽  
Anion Channel ◽  
Functional Responses ◽  
Voltage Dependent Anion Channel ◽  
Antagonistic Action ◽  
Mitochondrial Target ◽  
Voltage Dependent ◽  
Apoptotic Cascade

The mechanisms by which pro-apoptotic members of the Bcl-2 family of proteins promote the release of mitochondrial factors like cytochrome c, subsequently activating the apoptotic cascade, or by which anti-apoptotic family members block this release, are still not understood. When expressed in yeast, Bcl-2 family members act directly upon conserved mitochondrial components that correspond to their apoptotic substrates in mammalian cells. Here we describe a system in which the levels of representative pro- and anti-apoptotic members of the Bcl-2 family can be regulated independently in yeast. Using this system, we have focused on the action of the anti-apoptotic family member Bcl-xL, and have defined the quantitative relationships that underlie the antagonistic action of this protein on the lethal consequences of expression of the pro-apoptotic family member Bax. This system has also allowed us to demonstrate biochemically that Bcl-xL has two actions at the level of the mitochondrion. Bcl-xL is able to inhibit the stable integration of Bax into mitochondrial membranes, as well as hinder the action of Bax that does become stably integrated into these membranes. Taken together, our results suggest that both the functional and biochemical actions of Bcl-xL may be based on the ability of this molecule to disrupt the interaction of Bax with a resident mitochondrial target that is required for Bax action. Finally, we confirm that VDAC (voltage-dependent anion channel) is not required for the functional responses observed following the expression of either pro- or anti-apoptotic members of the Bcl-2 family.

scholarly journals Essential Role of Voltage-Dependent Anion Channel in Various Forms of Apoptosis in Mammalian Cells

2001 ◽  
Vol 152 (2) ◽  
pp. 237-250 ◽  
Author(s):  
Shigeomi Shimizu ◽  
Yosuke Matsuoka ◽  
Yasuo Shinohara ◽  
Yoshihiro Yoneda ◽  
Yoshihide Tsujimoto
Keyword(s):  
Cytochrome C ◽  
Mammalian Cells ◽  
Essential Role ◽  
Biological Significance ◽  
Anion Channel ◽  
Voltage Dependent Anion Channel ◽  
Cytochrome C Release ◽  
Isolated Mitochondria ◽  
Voltage Dependent ◽  
Induced Apoptosis

Through direct interaction with the voltage-dependent anion channel (VDAC), proapoptotic members of the Bcl-2 family such as Bax and Bak induce apoptogenic cytochrome c release in isolated mitochondria, whereas BH3-only proteins such as Bid and Bik do not directly target the VDAC to induce cytochrome c release. To investigate the biological significance of the VDAC for apoptosis in mammalian cells, we produced two kinds of anti-VDAC antibodies that inhibited VDAC activity. In isolated mitochondria, these antibodies prevented Bax-induced cytochrome c release and loss of the mitochondrial membrane potential (Δψ), but not Bid-induced cytochrome c release. When microinjected into cells, these anti-VDAC antibodies, but not control antibodies, also prevented Bax-induced cytochrome c release and apoptosis, whereas the antibodies did not prevent Bid-induced apoptosis, indicating that the VDAC is essential for Bax-induced, but not Bid-induced, apoptogenic mitochondrial changes and apoptotic cell death. In addition, microinjection of these anti-VDAC antibodies significantly inhibited etoposide-, paclitaxel-, and staurosporine-induced apoptosis. Furthermore, we used these antibodies to show that Bax- and Bak-induced lysis of red blood cells was also mediated by the VDAC on plasma membrane. Taken together, our data provide evidence that the VDAC plays an essential role in apoptogenic cytochrome c release and apoptosis in mammalian cells.

scholarly journals The Plasmodial Surface Anion Channel Is Functionally Conserved in Divergent Malaria Parasites

2005 ◽  
Vol 4 (12) ◽  
pp. 2153-2159 ◽  
Author(s):  
Godfrey Lisk ◽  
Sanjay A. Desai
Keyword(s):  
Copy Number ◽  
Plasmodium Knowlesi ◽  
Osmotic Fragility ◽  
Anion Channel ◽  
Parasite Growth ◽  
Anion Channels ◽  
Malaria Parasites ◽  
Voltage Dependent ◽  
Host Cell Surface ◽  
Exposed Location

ABSTRACT The plasmodial surface anion channel (PSAC), a novel ion channel induced on human erythrocytes infected with Plasmodium falciparum, mediates increased permeability to nutrients and presumably supports intracellular parasite growth. Isotope flux studies indicate that other malaria parasites also increase the permeability of their host erythrocytes, but the precise mechanisms are unknown. Channels similar to PSAC or alternative mechanisms, such as the upregulation of endogenous host transporters, might fulfill parasite nutrient demands. Here we evaluated these possibilities with rhesus monkey erythrocytes infected with Plasmodium knowlesi, a parasite phylogenetically distant from P. falciparum. Tracer flux and osmotic fragility studies revealed dramatically increased permeabilities paralleling changes seen after P. falciparum infection. Patch-clamp of P. knowlesi-infected rhesus erythrocytes revealed an anion channel with striking similarities to PSAC: its conductance, voltage-dependent gating, pharmacology, selectivity, and copy number per infected cell were nearly identical. Our findings implicate a family of unusual anion channels highly conserved on erythrocytes infected with various malaria parasites. Together with PSAC's exposed location on the host cell surface and its central role in transport changes after infection, this conservation supports development of antimalarial drugs against the PSAC family.

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