More than just a pressure relief valve: physiological roles of volume-regulated LRRC8 anion channels

2019 ◽  
Vol 400 (11) ◽  
pp. 1481-1496 ◽  
Author(s):  
Lingye Chen ◽  
Benjamin König ◽  
Tianbao Liu ◽  
Sumaira Pervaiz ◽  
Yasmin S. Razzaque ◽  
...  
Keyword(s):  
Volume Regulation ◽  
Regulatory Volume Decrease ◽  
Anion Channel ◽  
Therapy Resistance ◽  
Cell Swelling ◽  
Organic Osmolytes ◽  
Anion Channels ◽  
Relief Valve ◽  
Wide Range ◽  
And Migration

Abstract The volume-regulated anion channel (VRAC) is a key player in the volume regulation of vertebrate cells. This ubiquitously expressed channel opens upon osmotic cell swelling and potentially other cues and releases chloride and organic osmolytes, which contributes to regulatory volume decrease (RVD). A plethora of studies have proposed a wide range of physiological roles for VRAC beyond volume regulation including cell proliferation, differentiation and migration, apoptosis, intercellular communication by direct release of signaling molecules and by supporting the exocytosis of insulin. VRAC was additionally implicated in pathological states such as cancer therapy resistance and excitotoxicity under ischemic conditions. Following extensive investigations, 5 years ago leucine-rich repeat-containing family 8 (LRRC8) heteromers containing LRRC8A were identified as the pore-forming components of VRAC. Since then, molecular biological approaches have allowed further insight into the biophysical properties and structure of VRAC. Heterologous expression, siRNA-mediated downregulation and genome editing in cells, as well as the use of animal models have enabled the assessment of the proposed physiological roles, together with the identification of new functions including spermatogenesis and the uptake of antibiotics and platinum-based cancer drugs. This review discusses the recent molecular biological insights into the physiology of VRAC in relation to its previously proposed roles.

The volume-regulated anion channel is formed by LRRC8 heteromers – molecular identification and roles in membrane transport and physiology

2015 ◽  
Vol 396 (9-10) ◽  
pp. 975-990 ◽  
Author(s):  
Tobias Stauber
Keyword(s):  
Cell Biology ◽  
Regulatory Volume Decrease ◽  
Anion Channel ◽  
Cell Swelling ◽  
Transepithelial Transport ◽  
Organic Osmolytes ◽  
Physiological Processes ◽  
Starting Point ◽  
And Migration ◽  
Volume Decrease

Abstract Cellular volume regulation is fundamental for numerous physiological processes. The volume-regulated anion channel, VRAC, plays a crucial role in regulatory volume decrease. This channel, which is ubiquitously expressed in vertebrates, has been vastly characterized by electrophysiological means. It opens upon cell swelling and conducts chloride and arguably organic osmolytes. VRAC has been proposed to be critically involved in various cellular and organismal functions, including cell proliferation and migration, apoptosis, transepithelial transport, swelling-induced exocytosis and intercellular communication. It may also play a role in pathological states like cancer and ischemia. Despite many efforts, the molecular identity of VRAC had remained elusive for decades, until the recent discovery of heteromers of LRRC8A with other LRRC8 family members as an essential VRAC component. This identification marks a starting point for studies on the structure-function relation, for molecular biological investigations of its cell biology and for re-evaluating the physiological roles of VRAC. This review recapitulates the identification of LRRC8 heteromers as VRAC components, depicts the similarities between LRRC8 proteins and pannexins, and discussed whether VRAC conducts larger osmolytes. Furthermore, proposed physiological functions of VRAC and the present knowledge about the physiological significance of LRRC8 proteins are summarized and collated.

scholarly journals Purinergic activation of anion conductance and osmolyte efflux in cultured rat hippocampal neurons

2008 ◽  
Vol 295 (6) ◽  
pp. C1550-C1560 ◽  
Author(s):  
Guangze Li ◽  
James E. Olson
Keyword(s):  
Mammalian Cells ◽  
Hippocampal Neurons ◽  
Regulatory Volume Decrease ◽  
Extracellular Atp ◽  
Cell Swelling ◽  
Nucleotide Receptors ◽  
Organic Osmolytes ◽  
Anion Channels ◽  
Critical Signal ◽  
Current Activation

The majority of mammalian cells demonstrate regulatory volume decrease (RVD) following swelling caused by hyposmotic exposure. A critical signal initiating RVD is activation of nucleotide receptors by ATP. Elevated extracellular ATP in response to cytotoxic cell swelling during pathological conditions also may initiate loss of taurine and other intracellular osmolytes via anion channels. This study characterizes neuronal ATP-activated anion current and explores its role in net loss of amino acid osmolytes. To isolate anion currents, we used CsCl as the major electrolyte in patch electrode and bath solutions and blocked residual cation currents with NiCl2 and tetraethylammonium. Anion currents were activated by extracellular ATP with a Km of 70 μM and increased over fourfold during several minutes of ATP exposure, reaching a maximum after 9.0 min (SD 4.2). The currents were blocked by inhibitors of nucleotide receptors and volume-regulated anion channels (VRAC). Currents showed outward rectification and inactivation at highly depolarizing membrane potentials, characteristics of swelling-activated anion currents. P2X agonists failed to activate the anion current, and an inhibitor of P2X receptors did not block the effect of ATP. Furthermore, current activation was observed with extracellular ADP and 2-(methylthio)adenosine 5′-diphosphate, a P2Y1 receptor-specific agonist. Much less current activation was observed with extracellular UTP, suggesting the response is mediated predominantly by P2Y1 receptors. ATP caused a dose-dependent loss of taurine and alanine that could be blocked by inhibitors of VRAC. ATP did not inhibit the taurine uptake transporter. Thus extracellular ATP triggers a loss of intracellular organic osmolytes via activation of anion channels. This mechanism may facilitate neuronal volume homeostasis during cytotoxic edema.

scholarly journals Acid- and Volume-Sensitive Chloride Currents in Microglial Cells

2019 ◽  
Vol 20 (14) ◽  
pp. 3475 ◽  
Author(s):  
Michael Kittl ◽  
Katharina Helm ◽  
Marlena Beyreis ◽  
Christian Mayr ◽  
Martin Gaisberger ◽  
...  
Keyword(s):  
Cell Volume ◽  
Volume Regulation ◽  
Regulatory Volume Decrease ◽  
Cell Volume Regulation ◽  
Cell Types ◽  
Microglial Cells ◽  
Cell Swelling ◽  
Mean Cell Volume ◽  
Current Activation ◽  
And Migration

Many cell types express an acid-sensitive outwardly rectifying (ASOR) anion current of an unknown function. We characterized such a current in BV-2 microglial cells and then studied its interrelation with the volume-sensitive outwardly rectifying (VSOR) Cl− current and the effect of acidosis on cell volume regulation. We used patch clamp, the Coulter method, and the pH-sensitive dye BCECF to measure Cl− currents and cell membrane potentials, mean cell volume, and intracellular pH, respectively. The ASOR current activated at pH ≤ 5.0 and displayed an I− > Cl− > gluconate− permeability sequence. When compared to the VSOR current, it was similarly sensitive to DIDS, but less sensitive to DCPIB, and insensitive to tamoxifen. Under acidic conditions, the ASOR current was the dominating Cl− conductance, while the VSOR current was apparently inactivated. Acidification caused cell swelling under isotonic conditions and prevented the regulatory volume decrease under hypotonicity. We conclude that acidification, associated with activation of the ASOR- and inactivation of the VSOR current, massively impairs cell volume homeostasis. ASOR current activation could affect microglial function under acidotoxic conditions, since acidosis is a hallmark of pathophysiological events like inflammation, stroke or ischemia and migration and phagocytosis in microglial cells are closely related to cell volume regulation.

The volume-sensitive organic osmolyte-anion channel VSOAC is regulated by nonhydrolytic ATP binding

1994 ◽  
Vol 267 (5) ◽  
pp. C1203-C1209 ◽  
Author(s):  
P. S. Jackson ◽  
R. Morrison ◽  
K. Strange
Keyword(s):  
Ketone Bodies ◽  
Anion Channel ◽  
Metabolic Inhibitors ◽  
Cell Swelling ◽  
Organic Osmolytes ◽  
Pipette Solution ◽  
Organic Osmolyte ◽  
Atp Levels ◽  
Patch Pipette ◽  
Taurine Efflux

Efflux of intracellular organic osmolytes to the external medium is a ubiquitous response to cell swelling. Accumulating evidence indicates that volume regulatory loss of structurally unrelated organic osmolytes from cells is mediated by a relatively nonselective volume-sensitive anion channel. In C6 cells, we have termed this channel VSOAC for volume-sensitive organic osmolyte-anion channel. Swelling-induced activation of VSOAC required the presence of ATP or nonhydrolyzable ATP analogues [adenosine 5'-O-(3-thiotriphosphate), adenylylmethyl-enediphosphonate (AMP-PCP), or 5'-adenylylimidodiphosphate] in the patch pipette. Sustained activation of VSOAC also required ATP. Channel rundown was observed when cellular ATP levels were lowered by intracellular dialysis with the patch pipette solution. Rundown was prevented by the ATP analogue AMP-PCP. Passive swelling-induced myo-[3H]inositol and [3H]taurine efflux was blocked by metabolic inhibitors that decreased cellular ATP levels. Titration of cellular ATP levels with azide demonstrated that the apparent dissociation constant (Kd) for ATP of both myo-inositol and taurine efflux was approximately 1.7 mM. The high Kd for ATP indicates that cellular metabolic state plays an important role in modulating organic osmolyte loss. Regulation of VSOAC activity by ATP prevents depletion of metabolically expensive organic osmolytes when cellular energy production is reduced. In addition, ATP-dependent regulation provides essential feedback to minimize the loss of energy-producing carbon sources such as pyruvate, short-chain fatty acids, ketone bodies, and amino acids, which readily permeate this channel.

Dihydropyridine-sensitive cell volume regulation in proximal tubule: the calcium window

1990 ◽  
Vol 259 (6) ◽  
pp. F950-F960 ◽  
Author(s):  
N. A. McCarty ◽  
R. G. O'Neil
Keyword(s):  
Cell Volume ◽  
Volume Regulation ◽  
Regulatory Volume Decrease ◽  
Cell Volume Regulation ◽  
Cell Swelling ◽  
Channel Blockers ◽  
Ca Channel ◽  
Hypotonic Solution ◽  
Dependent Manner ◽  
Intracellular Ca

The mechanism underlying the activation of hypotonic cell volume regulation was studied in rabbit proximal straight tubule (PST). When isolated non-perfused tubules were exposed to hypotonic solution, cells swelled rapidly and then underwent a regulatory volume decrease (RVD). The extent of regulation after swelling was highly dependent on extracellular Ca concentration ([Ca2+]o), with a half-maximal inhibition (K1/2) for [Ca2+]o of approximately 100 microM. RVD was blocked by the Ca-channel blockers verapamil, lanthanum, and the dihydropyridines (DHP) nifedipine and nitrendipine, implicating voltage-activated Ca channels in the RVD response. Using the fura-2 fluorescence-ratio technique, we observed that cell swelling caused a sustained rise in intracellular Ca ([Ca2+]i) only when [Ca2+]o was normal (1 mM) but not when [Ca2+]o was low (1-10 microM). Furthermore, external Ca was required early on during swelling to induce RVD. If RVD was initially blocked by reducing [Ca2+]o or by addition of verapamil during hypotonic swelling, volume regulation could only be restored by subsequently inducing Ca entry within the first 1 min or less of exposure to hypotonic solution. These data indicate a "calcium window" of less than 1 min, during which RVD is sensitive to Ca, and that part of the Ca-dependent mechanism responsible for achieving RVD undergoes inactivation after swelling. It is concluded that RVD in rabbit PST is modulated by Ca via a DHP-sensitive mechanism in a time-dependent manner.

scholarly journals Cell Death Induction and Protection by Activation of Ubiquitously Expressed Anion/Cation Channels. Part 2: Functional and Molecular Properties of ASOR/PAC Channels and Their Roles in Cell Volume Dysregulation and Acidotoxic Cell Death

2021 ◽  
Vol 9 ◽  
Author(s):  
Yasunobu Okada ◽  
Kaori Sato-Numata ◽  
Ravshan Z. Sabirov ◽  
Tomohiro Numata
Keyword(s):  
Cell Death ◽  
Cell Volume ◽  
Apoptotic Cell ◽  
Cell Volume Regulation ◽  
Anion Channel ◽  
Cell Swelling ◽  
Dimensional Structure ◽  
Cation Channels ◽  
Anion Channels ◽  
Animal Cells

For survival and functions of animal cells, cell volume regulation (CVR) is essential. Major hallmarks of necrotic and apoptotic cell death are persistent cell swelling and shrinkage, and thus they are termed the necrotic volume increase (NVI) and the apoptotic volume decrease (AVD), respectively. A number of ubiquitously expressed anion and cation channels play essential roles not only in CVR but also in cell death induction. This series of review articles address the question how cell death is induced or protected with using ubiquitously expressed ion channels such as swelling-activated anion channels, acid-activated anion channels, and several types of TRP cation channels including TRPM2 and TRPM7. In the Part 1, we described the roles of swelling-activated VSOR/VRAC anion channels. Here, the Part 2 focuses on the roles of the acid-sensitive outwardly rectifying (ASOR) anion channel, also called the proton-activated chloride (PAC) anion channel, which is activated by extracellular protons in a manner sharply dependent on ambient temperature. First, we summarize phenotypical properties, the molecular identity, and the three-dimensional structure of ASOR/PAC. Second, we highlight the unique roles of ASOR/PAC in CVR dysfunction and in the induction of or protection from acidotoxic cell death under acidosis and ischemic conditions.

Swelling-activated efflux of taurine and other organic osmolytes in endothelial cells

1997 ◽  
Vol 273 (1) ◽  
pp. C214-C222 ◽  
Author(s):  
V. G. Manolopoulos ◽  
T. Voets ◽  
P. E. Declercq ◽  
G. Droogmans ◽  
B. Nilius
Keyword(s):  
Endothelial Cells ◽  
Anion Channel ◽  
Disulfonic Acid ◽  
Channel Blockers ◽  
Organic Osmolytes ◽  
Dependent Manner ◽  
Anion Channels ◽  
Whole Cell Patch Clamp ◽  
Osmolyte Efflux ◽  
Dose Dependent

We used a combined biochemical, pharmacological, and electrophysiological approach to study the effects of hyposmotic swelling on organic osmolyte efflux in endothelial cells (EC). In [3H]taurine-loaded monolayers of calf pulmonary artery EC (CPAEC), hyposmolality activated time- and dose-dependent effluxes of [3H]taurine. Swelling-activated [3H]taurine efflux (Jtau swell)in CPAEC was inhibited by the anion channel blockers tamoxifen, 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), fenamates, and also quinine (in a pH-dependent manner), ATP, and the phospholipase A2 inhibitor 4-bromophenacyl bromide. In contrast, Jtau swell was partly or totally insensitive to bumetanide, forskolin, phorbol 12-myristate 13-acetate, and staurosporine. Swelling also activated myo-[3H]inositol efflux that was blocked by tamoxifen, NPPB, DIDS, and niflumic acid. Moreover, the cellular content of taurine and other amino acids was significantly reduced in osmotically activated CPAEC. Finally, in whole cell patch-clamp experiments, taurine, glycine, aspartate, and glutamate exhibited significant permeability for swelling-activated anion channels. In conclusion, hyposmotic swelling activates efflux of taurine and other organic osmolytes in EC. In addition, our results suggest that anion channels may provide a pathway for swelling-activated efflux of organic osmolytes in EC.

scholarly journals Requirement for an intact cytoskeleton for volume regulation in boar spermatozoa

Reproduction ◽  
2004 ◽  
Vol 127 (1) ◽  
pp. 105-115 ◽  
Author(s):  
A M Petrunkina ◽  
M Hebel ◽  
D Waberski ◽  
K F Weitze ◽  
E Töpfer-Petersen
Keyword(s):  
Cell Volume ◽  
Volume Regulation ◽  
Regulatory Volume Decrease ◽  
Cytochalasin D ◽  
Cell Swelling ◽  
Microtubule Network ◽  
Regulatory Ability ◽  
Boar Sperm ◽  
Volume Response ◽  
Boar Spermatozoa

Osmotically induced cell swelling triggers a chain of events leading to a net loss of major cell ions and water, resulting in cell volume recovery, a process known as regulatory volume decrease (RVD). In many cell types, there is an evidence that the cytoskeleton may play a role in the initial sensing and transduction of the signal of volume change. In this study, we tested the hypothesis that an intact microfilament and microtubule network is required for volume response and RVD in boar sperm before and after capacitation treatment and whether addition of cytochalasin D and colchicine to the capacitation medium would affect volumetric behaviour. Capacitation is a series of cellular and molecular alterations that enable the spermatozoon to fertilize an oocyte. Cell volume measurements of washed sperm suspensions were performed electronically in Hepes-buffered saline solutions of 300 and 180 mosmol/kg. After exposure to hypoosmotic conditions, boar sperm showed initial swelling (up to 150% of initial volume within 5 min), which was subsequently partially reversed (to about 120–130% after 20 min). Treatment with cytochalasin D led to reduced initial swelling (1 μmol/l) and loss of RVD in washed sperm (1–10 μmol/l) and at the beginning of incubation under capacitating conditions (5 μmol/l). Short treatment with 500 μmol/l colchicine affected the volume regulatory ability in sperm under capacitating conditions but not in washed sperm. No significant differences in cell volume response were observed after subsequent addition of cytochalasin D and colchicine to the suspensions of sperm incubated for 3 h under capacitating conditions. However, the incubation under capacitating conditions in the presence of cytochalasin D led to improved volume regulation at the end of the incubation period (23%). The microfilament network appears to be important for volume regulation in washed boar spermatozoa while intact microtubules do not seem to be necessary for osmotically induced RVD. The changes in cytoskeleton microfilament organization during capacitation, possibly affecting the osmotically induced volume response, appear to occur at the later stages of capacitation, whereas changes in microtubules, related to volume regulatory ability, may be programmed within the first stages of capacitation.

Taurine transport in skate hepatocytes. II. Volume activation, energy, and sulfhydryl dependence

1992 ◽  
Vol 262 (3) ◽  
pp. G451-G460 ◽  
Author(s):  
N. Ballatori ◽  
J. L. Boyer
Keyword(s):  
Plasma Membrane ◽  
Concentration Gradient ◽  
Regulatory Volume Decrease ◽  
Metabolic Inhibitors ◽  
Cell Swelling ◽  
Disulfonic Acid ◽  
Organic Osmolytes ◽  
Taurine Transport ◽  
Taurine Concentration ◽  
Taurine Efflux

Isolated skate (Raja erinacea) hepatocytes swollen in hypotonic media exhibited a regulatory volume decrease (RVD) that was associated with only a small increase in K+ or 86Rb+ efflux but a substantial increase in the release of taurine, an amino acid found in high concentrations in skate hepatocytes. Taurine efflux was stimulated in media made hypotonic by addition of H2O or removal of NaCl, as well as in cells swollen in isotonic media containing rapidly penetrating solutes (202 mM ethylene glycol or 202 mM additional urea substituted for 101 mM NaCl), suggesting that cell swelling rather than hyposmolarity is the stimulus for the activation of taurine release. In contrast, release of glutathione, L-[14C]alanine and other alpha-amino acids (e.g., threonine, serine, glutamate, glutamine, glycine, or valine) was unaffected by dilution with 40% H2O. Taurine efflux was not altered by replacement of extracellular Na+ with choline+ or K+ and was only slightly diminished by replacing Cl- with NO3-. Addition of 50 mM taurine or hypotaurine to the incubation media also had no effect on volume-stimulated [14C]taurine efflux, suggesting that the taurine concentration gradient across the plasma membrane is not the driving force. Volume-stimulated taurine transport was temperature sensitive, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid inhibitable (0.5 mM), and nearly completely blocked by metabolic inhibitors (2,4-dinitrophenol, KCN, sodium azide, oligomycin, carbonyl cyanide m-chlorophenylhydrazone, and antimycin A), suggesting an active energy-dependent process. Sulfhydryl-reactive reagents (N-ethylmaleimide, diamide, iodoacetate, tert-butyl hydroperoxide, and mercury) also blocked volume-stimulated taurine efflux, whereas efflux was unaffected by Ca2+ ionophore, phorbol ester, dibutyryl-adenosine 3',5'-cyclic monophosphate, vasopressin, or pretreatment with ouabain or furosemide. N-ethylmaleimide, diamide, 2,4-dinitrophenol, and iodoacetate plus KCN also inhibited the RVD. These findings suggest that, in contrast to hepatocytes from most vertebrate species, RVD in skate hepatocytes is associated with the release of only a small fraction of intracellular K+ but a substantial fraction of intracellular taurine and perhaps other organic osmolytes. This volume-activated taurine transport mechanism is energy and sulfhydryl group dependent and is not related to the taurine concentration gradient across the skate hepatocyte plasma membrane.

scholarly journals Indirect Role of AQP4b and AQP4d Isoforms in Dynamics of Astrocyte Volume and Orthogonal Arrays of Particles

Cells ◽  
2020 ◽  
Vol 9 (3) ◽  
pp. 735 ◽  
Author(s):  
Marjeta Lisjak ◽  
Maja Potokar ◽  
Robert Zorec ◽  
Jernej Jorgačevski
Keyword(s):  
Plasma Membrane ◽  
Cell Volume ◽  
Volume Regulation ◽  
Water Channel ◽  
Regulatory Volume Decrease ◽  
Cell Volume Regulation ◽  
Orthogonal Arrays ◽  
Cell Swelling ◽  
Early Endosomes ◽  
Orthogonal Arrays Of Particles

Water channel aquaporin 4 (AQP4) plays a key role in the regulation of water homeostasis in the central nervous system (CNS). It is predominantly expressed in astrocytes lining blood–brain and blood–liquor boundaries. AQP4a (M1), AQP4c (M23), and AQP4e, present in the plasma membrane, participate in the cell volume regulation of astrocytes. The function of their splicing variants, AQP4b and AQP4d, predicted to be present in the cytoplasm, is unknown. We examined the cellular distribution of AQP4b and AQP4d in primary rat astrocytes and their role in cell volume regulation. The AQP4b and AQP4d isoforms exhibited extensive cytoplasmic localization in early and late endosomes/lysosomes and in the Golgi apparatus. Neither isoform localized to orthogonal arrays of particles (OAPs) in the plasma membrane. The overexpression of AQP4b and AQP4d isoforms in isoosmotic conditions reduced the density of OAPs; in hypoosmotic conditions, they remained absent from OAPs. In hypoosmotic conditions, the AQP4d isoform was significantly redistributed to early endosomes, which correlated with the increased trafficking of AQP4-laden vesicles. The overexpression of AQP4d facilitated the kinetics of cell swelling, without affecting the regulatory volume decrease. Therefore, although they reside in the cytoplasm, AQP4b and AQP4d isoforms may play an indirect role in astrocyte volume changes.

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