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Anion Channel
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Yasunobu Okada – One of the best experts on this subject based on the ideXlab platform.
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Biophysics and Physiology of the Volume-Regulated Anion Channel (VRAC)/Volume-Sensitive Outwardly Rectifying Anion Channel (VSOR)
Pflügers Archiv – European Journal of Physiology, 2016Co-Authors: Stine F. Pedersen, Yasunobu Okada, Bernd NiliusAbstract:The volume-regulated Anion Channel (VRAC), also known as the volume-sensitive outwardly rectifying (VSOR) Anion Channel or the volume-sensitive organic osmolyte/Anion Channel (VSOAC), is essential for cell volume regulation after swelling in most vertebrate cell types studied to date. In addition to its role in cell volume homeostasis, VRAC has been implicated in numerous other physiological and pathophysiological processes, including cancer, ischemic brain edema, cell motility, proliferation, angiogenesis, programmed cell death, and excitotoxic glutamate release. Although VRAC has been extensively biophysically, pharmacologically, and functionally characterized, its molecular identity was highly controversial until the recent identification of the leucine-rich repeats containing 8A (LRRC8A) protein as essential for the VRAC current in multiple cell types and a likely pore-forming subunit of VRAC. Members of this distantly pannexin-1-related protein family form heteromers, and in addition to LRRC8A, at least another LRRC8 family member is required for the formation of a functional VRAC. This review summarizes the biophysical and pharmacological properties of VRAC, highlights its main physiological functions and pathophysiological implications, and outlines the search for its molecular identity.
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Distinct pharmacological and molecular properties of the acid-sensitive outwardly rectifying (ASOR) Anion Channel from those of the volume-sensitive outwardly rectifying (VSOR) Anion Channel
Pflugers Archiv : European journal of physiology, 2016Co-Authors: Kaori Sato-numata, Tomohiro Numata, Ryuji Inoue, Yasunobu OkadaAbstract:Expressed by many cell types, acid-sensitive outwardly rectifying (ASOR) Anion Channels are known to be activated by extracellular acidification and involved in acidotoxic necrotic cell death. In contrast, ubiquitously expressed volume-sensitive outwardly rectifying (VSOR) Anion Channels are activated by osmotic cell swelling and involved in cell volume regulation and apoptotic cell death. Distinct inhibitors to distinguish ASOR from VSOR Anion Channels have not been identified. Although leucine-rich repeats containing 8A (LRRC8A) was recently found to be an essential component of VSOR Anion Channels, the possibility of an LRRC8 family member serving as a component of ASOR Anion Channels has not been examined. In this study, we explored the effects of 12 known VSOR Channel inhibitors and small interfering RNA (siRNA)-mediated knockdown of LRRC8 family members on ASOR and VSOR currents in HeLa cells. Among these inhibitors, eight putative VSOR blockers, including 4-(2-butyl-6,7-dichlor-2-cyclopentylindan-1-on-5-yl) oxobutyric acid (DCPIB) and 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB), were totally ineffective at blocking ASOR Channel activity, whereas suramin, R-(+)-[(2-n-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy] acetic acid (DIOA), arachidonic acid, and niflumic acid were found to be effective ASOR Anion Channel antagonists. In addition, gene-silencing studies showed that no LRRC8 family members are essentially involved in ASOR Anion Channel activity, whereas LRRC8A is involved in VSOR Anion Channel activity in HeLa cells.
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Characteristics and roles of the volume-sensitive outwardly rectifying (VSOR) Anion Channel in the central nervous system
Neuroscience, 2014Co-Authors: Tenpei Akita, Yasunobu OkadaAbstract:Cell volume regulation (CVR) is essential for all types of cells in the central nervous system (CNS) to counteract cell volume changes that may be associated with neuronal activities or diseases and with osmosensing in the hypothalamus, to facilitate morphological changes during cell proliferation, differentiation and migration, and to execute apoptosis of cells. The regulation is attained by regulating the net influx or efflux of solutes and water across the plasma membrane. The volume-sensitive outwardly rectifying (VSOR) Anion Channel plays a major role in providing a pathway for Anion flux during the regulation. The VSOR Anion Channel is permeable not only to Cl(-) ions but also to amino acids like glutamate and taurine. This property confers a means of intercellular communications through the opening of the Channel in the CNS. Thus exploring the roles of VSOR Anion Channels is crucial to understand the basic principles of cellular functions in the CNS. Here we review biophysical and pharmacological characteristics of the VSOR Anion Channel in the CNS, discuss its activation mechanisms and roles in the CNS reported so far, and give some perspectives on the next issues to be examined in the near future.
Triin Vahisalu – One of the best experts on this subject based on the ideXlab platform.
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slac1 is required for plant guard cell s type Anion Channel function in stomatal signalling
Nature, 2008Co-Authors: Triin Vahisalu, Hannes Kollist, Yongfei Wang, Noriyuki Nishimura, Waiyin Chan, Gabriel Valerio, Airi Lamminmaki, Mikael BroscheAbstract:The stomata on the undersides of leaves control the exchange of carbon dioxide and water between plants and the atmosphere. Stomatal pore aperture is regulated by transport of ions and metabolites across guard-cell membranes. Perhaps surprisingly, until now no plant plasma membrane Anion Channel subunits have been cloned — and the homologues of animal Anion Channels have been shown not to encode functional ion Channels in plants. Now two groups working independently have identified a protein that is an essential component for S-type Anion Channel function and is required for stomatal closure in response to a variety of physiological and stress stimuli. Termed SLAC1, it is a distant homologue of fungal and bacterial dicarboxylate/malic acid transport proteins. One of two related studies that describe the identification of a protein which is an essential component for S-type Anion Channel function and is required for stomatal closure in response to a variety of physiological and stress stimuli including carbon dioxide and ozone. Stomatal pores, formed by two surrounding guard cells in the epidermis of plant leaves, allow influx of atmospheric carbon dioxide in exchange for transpirational water loss. Stomata also restrict the entry of ozone — an important air pollutant that has an increasingly negative impact on crop yields, and thus global carbon fixation1 and climate change2. The aperture of stomatal pores is regulated by the transport of osmotically active ions and metabolites across guard cell membranes3,4. Despite the vital role of guard cells in controlling plant water loss3,4, ozone sensitivity1,2 and CO2 supply2,5,6,7, the genes encoding some of the main regulators of stomatal movements remain unknown. It has been proposed that guard cell Anion Channels function as important regulators of stomatal closure and are essential in mediating stomatal responses to physiological and stress stimuli3,4,8. However, the genes encoding membrane proteins that mediate guard cell Anion efflux have not yet been identified. Here we report the mapping and characterization of an ozone-sensitive Arabidopsis thaliana mutant, slac1. We show that SLAC1 (SLOW Anion Channel-ASSOCIATED 1) is preferentially expressed in guard cells and encodes a distant homologue of fungal and bacterial dicarboxylate/malic acid transport proteins. The plasma membrane protein SLAC1 is essential for stomatal closure in response to CO2, abscisic acid, ozone, light/dark transitions, humidity change, calcium ions, hydrogen peroxide and nitric oxide. Mutations in SLAC1 impair slow (S-type) Anion Channel currents that are activated by cytosolic Ca2+ and abscisic acid, but do not affect rapid (R-type) Anion Channel currents or Ca2+ Channel function. A low homology of SLAC1 to bacterial and fungal organic acid transport proteins, and the permeability of S-type Anion Channels to malate9 suggest a vital role for SLAC1 in the function of S-type Anion Channels.
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slac1 is required for plant guard cell s type Anion Channel function in stomatal signalling
Nature, 2008Co-Authors: Triin Vahisalu, Mikael Brosche, Hannes Kollist, Yongfei Wang, Noriyuki Nishimura, Waiyin Chan, Gabriel Valerio, Airi Lamminmaki, Heino MoldauAbstract:Stomatal pores, formed by two surrounding guard cells in the epidermis of plant leaves, allow influx of atmospheric carbon dioxide in exchange for transpirational water loss. Stomata also restrict the entry of ozone–an important air pollutant that has an increasingly negative impact on crop yields, and thus global carbon fixation and climate change. The aperture of stomatal pores is regulated by the transport of osmotically active ions and metabolites across guard cell membranes. Despite the vital role of guard cells in controlling plant water loss, ozone sensitivity and CO2 supply, the genes encoding some of the main regulators of stomatal movements remain unknown. It has been proposed that guard cell Anion Channels function as important regulators of stomatal closure and are essential in mediating stomatal responses to physiological and stress stimuli. However, the genes encoding membrane proteins that mediate guard cell Anion efflux have not yet been identified. Here we report the mapping and characterization of an ozone-sensitive Arabidopsis thaliana mutant, slac1. We show that SLAC1 (SLOW Anion Channel-ASSOCIATED 1) is preferentially expressed in guard cells and encodes a distant homologue of fungal and bacterial dicarboxylate/malic acid transport proteins. The plasma membrane protein SLAC1 is essential for stomatal closure in response to CO2, abscisic acid, ozone, light/dark transitions, humidity change, calcium ions, hydrogen peroxide and nitric oxide. Mutations in SLAC1 impair slow (S-type) Anion Channel currents that are activated by cytosolic Ca2+ and abscisic acid, but do not affect rapid (R-type) Anion Channel currents or Ca2+ Channel function. A low homology of SLAC1 to bacterial and fungal organic acid transport proteins, and the permeability of S-type Anion Channels to malate suggest a vital role for SLAC1 in the function of S-type Anion Channels.
Dietmar Geiger – One of the best experts on this subject based on the ideXlab platform.
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the desert plant phoenix dactylifera closes stomata via nitrate regulated slac1 Anion Channel
New Phytologist, 2017Co-Authors: Heike M Muller, Dietmar Geiger, Hubert Bauer, Nadine Schafer, Silke Lautner, Jorg Fromm, Markus Riederer, Amauri Bueno, Thomas Nussbaumer, Klaus F X MayerAbstract:Date palm Phoenix dactylifera is a desert crop well adapted to survive and produce fruits under extreme drought and heat. How are palms under such harsh environmental conditions able to limit transpirational water loss? Here, we analysed the cuticular waxes, stomata structure and function, and molecular biology of guard cells from P. dactylifera. To understand the stomatal response to the water stress phytohormone of the desert plant, we cloned the major elements necessary for guard cell fast abscisic acid (ABA) signalling and reconstituted this ABA signalosome in Xenopus oocytes. The PhoenixSLAC1-type Anion Channel is regulated by ABA kinase PdOST1. Energy-dispersive X-ray analysis (EDXA) demonstrated that date palm guard cells release chloride during stomatal closure. However, in Cl- medium, PdOST1 did not activate the desert plant Anion Channel PdSLAC1 per se. Only when nitrate was present at the extracellular face of the Anion Channel did the OST1-gated PdSLAC1 open, thus enabling chloride release. In the presence of nitrate, ABA enhanced and accelerated stomatal closure. Our findings indicate that, in date palm, the guard cell osmotic motor driving stomatal closure uses nitrate as the signal to open the major Anion Channel SLAC1. This initiates guard cell depolarization and the release of Anions together with potassium.
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Arabidopsis nanodomain-delimited ABA signaling pathway regulates the Anion Channel SLAH3
Proceedings of the National Academy of Sciences of the United States of America, 2013Co-Authors: Fatih Demir, Claudia Horntrich, Jörg O. Blachutzik, Sönke Scherzer, Yvonne Reinders, Sylwia Kierszniowska, Waltraud X. Schulze, Gregory S. Harms, Rainer Hedrich, Dietmar GeigerAbstract:The phytohormone abscisic acid (ABA) plays a key role in the plant response to drought stress. Hence, ABA-dependent gene transcription and ion transport is regulated by a variety of protein kinases and phosphatases. However, the nature of the membrane-delimited ABA signal transduction steps remains largely unknown. To gain insight into plasma membrane-bound ABA signaling, we identified sterol-dependent proteins associated with detergent resistant membranes from Arabidopsis thaliana mesophyll cells. Among those, we detected the central ABA signaling phosphatase ABI1 (abscisic-acid insensitive 1) and the calcium-dependent protein kinase 21 (CPK21). Using fluorescence microscopy, we found these proteins to localize in membrane nanodomains, as observed by colocalization with the nanodomain marker remorin Arabidopsis thaliana remorin 1.3 (AtRem 1.3). After transient coexpression, CPK21 interacted with SLAH3 [slow Anion Channel 1 (SLAC1) homolog 3] and activated this Anion Channel. Upon CPK21 stimulation, SLAH3 exhibited the hallmark properties of S-type Anion Channels. Coexpression of SLAH3/CPK21 with ABI1, however, prevented proper nanodomain localization of the SLAH3/CPK21 protein complex, and as a result Anion Channel activation failed. FRET studies revealed enhanced interaction of SLAH3 and CPK21 within the plasma membrane in response to ABA and thus confirmed our initial observations. Interestingly, the ABA-induced SLAH3/CPK21 interaction was modulated by ABI1 and the ABA receptor RCAR1/PYL9 [regulatory components of ABA receptor 1/PYR1 (pyrabactin resistance 1)-like protein 9]. We therefore propose that ABA signaling via inhibition of ABI1 modulates the apparent association of a signaling and transport complex within membrane domains that is necessary for phosphorylation and activation of the S-type Anion Channel SLAH3 by CPK21.
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Open stomata 1 (OST1) kinase controls R-type Anion Channel QUAC1 in Arabidopsis guard cells.
The Plant journal : for cell and molecular biology, 2013Co-Authors: Dennis Imes, Dietmar Geiger, Patrick Mumm, Irene Marten, Jennifer Böhm, Khaled A. S. Al-rasheid, Rainer HedrichAbstract:Under drought stress, the stress hormone ABA addresses the SnR kinase OST1 via its cytosolic receptor and the protein phosphatase ABI1. Upon activation, OST1 phosphorylates the guard cell S–type Anion Channel SLAC1. Arabidopsis ABI1 and OST1 loss-of-function mutants are characterized by an extreme wilting ‘open stomata′ phenotype. Given the fact that guard cells express both SLAC- and R–/QUAC-type Anion Channels, we questioned whether OST1, besides SLAC1, also controls the QUAC1 Channel. In other words, are ABI1/OST1 defects preventing both of the guard cell Anion Channel types from operating properly in terms of stomatal closure? The activation of the R–/QUAC-type Anion Channel by ABA signaling kinase OST1 and phosphatase ABI1 was analyzed in two experimental systems: Arabidopsis guard cells and the plant cell-free background of Xenopus oocytes . Patch-clamp studies on guard cells show that ABA activates R–/QUAC-type currents of wild-type plants, but to a much lesser extent in those of abi1–1 and ost1–2 mutants. In the oocyte system the co-expression of QUAC1 and OST1 resulted in a pronounced activation of the R–type Anion Channel. These studies indicate that OST1 is addressing both S–/SLAC- and R–/QUAC-type guard cell Anion Channels, and explain why the ost1–2 mutant is much more sensitive to drought than single slac1 or quac1 mutants.