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Molecular Identities and ATP Release Activities of Two Types of Volume-Regulatory Anion Channels, VSOR and Maxi-Cl. CURRENT TOPICS IN MEMBRANES 2018; 81:125-176. [PMID: 30243431 DOI: 10.1016/bs.ctm.2018.07.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
An elaborate volume regulation system based on interplay of ion channels and transporters was evolved to cope with constant osmotic challenges caused by intensive metabolism, transport and other physiological/pathophysiological events. In animal cells, two types of anion channels are directly activated by cell swelling and involved in the regulatory volume decrease (RVD): volume-sensitive outwardly rectifying anion channel (VSOR), also called volume-regulated anion channel (VRAC), and Maxi-Cl which is the most major type of maxi-anion channel (MAC). These two channels have very different biophysical profiles and exhibit opposite dependence on intracellular ATP. After several decades of verifying many false-positive candidates for VSOR and Maxi-Cl, LRRC8 family proteins emerged as major VSOR components, and SLCO2A1 protein as a core of Maxi-Cl. Still, neither of these proteins alone can fully reproduce the native channel phenotypes suggesting existence of missing components. Although both VSOR and Maxi-Cl have pores wide enough to accommodate bulky ATP4- and MgATP2- anions, evidence accumulated hitherto, based on pharmacological and gene silencing experiments, suggests that Maxi-Cl, but not VSOR, serves as one of the major pathways for the release of ATP from swollen and ischemic/hypoxic cells. Relations of VSOR and Maxi-Cl with diseases and their selective pharmacology are the topics promoted by recent advance in molecular identification of the two volume-activated, volume-regulatory anion channels.
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Jentsch TJ, Pusch M. CLC Chloride Channels and Transporters: Structure, Function, Physiology, and Disease. Physiol Rev 2018; 98:1493-1590. [DOI: 10.1152/physrev.00047.2017] [Citation(s) in RCA: 214] [Impact Index Per Article: 35.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
CLC anion transporters are found in all phyla and form a gene family of eight members in mammals. Two CLC proteins, each of which completely contains an ion translocation parthway, assemble to homo- or heteromeric dimers that sometimes require accessory β-subunits for function. CLC proteins come in two flavors: anion channels and anion/proton exchangers. Structures of these two CLC protein classes are surprisingly similar. Extensive structure-function analysis identified residues involved in ion permeation, anion-proton coupling and gating and led to attractive biophysical models. In mammals, ClC-1, -2, -Ka/-Kb are plasma membrane Cl−channels, whereas ClC-3 through ClC-7 are 2Cl−/H+-exchangers in endolysosomal membranes. Biological roles of CLCs were mostly studied in mammals, but also in plants and model organisms like yeast and Caenorhabditis elegans. CLC Cl−channels have roles in the control of electrical excitability, extra- and intracellular ion homeostasis, and transepithelial transport, whereas anion/proton exchangers influence vesicular ion composition and impinge on endocytosis and lysosomal function. The surprisingly diverse roles of CLCs are highlighted by human and mouse disorders elicited by mutations in their genes. These pathologies include neurodegeneration, leukodystrophy, mental retardation, deafness, blindness, myotonia, hyperaldosteronism, renal salt loss, proteinuria, kidney stones, male infertility, and osteopetrosis. In this review, emphasis is laid on biophysical structure-function analysis and on the cell biological and organismal roles of mammalian CLCs and their role in disease.
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Affiliation(s)
- Thomas J. Jentsch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany; and Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy
| | - Michael Pusch
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP) and Max-Delbrück-Centrum für Molekulare Medizin (MDC), Berlin, Germany; and Istituto di Biofisica, Consiglio Nazionale delle Ricerche, Genova, Italy
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Yu Y, Ye L, Li YG, Burkin DJ, Duan DD. Heart-specific overexpression of the human short CLC-3 chloride channel isoform limits myocardial ischemia-induced ERP and QT prolongation. Int J Cardiol 2016; 214:218-24. [PMID: 27064645 PMCID: PMC4862918 DOI: 10.1016/j.ijcard.2016.03.191] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Revised: 03/16/2016] [Accepted: 03/26/2016] [Indexed: 10/22/2022]
Abstract
INTRODUCTION Ischemia causes myocardial infarction and arrhythmias. Up-regulation of cardiac CLC-3 chloride channels is important for ischemic preconditioning-induced second-window protection against myocardial infarction. But its consequences in ischemia-induced electrical remodeling are still unknown. METHODS The recently-characterized heart-specific overexpression of human short CLC-3 isoform (hsCLC-3(OE)) mice was used to study the effects of CLC-3 up-regulation on cardiac electrophysiology under ischemia/reperfusion conditions. In vivo surface electrocardiography (ECG) and intracardiac electrophysiology (ICEP) were used to compare the electrophysiological properties of age-matched wild-type (Clcn3(+/+)) and hsCLC-3(OE) mice under control and myocardial ischemia-reperfusion conditions. RESULTS QT and QTc intervals of hsCLC-3(OE) mice were significantly shorter than those of Clcn3(+/+) mice under control, ischemia and reperfusion conditions. In the ICEP, ventricular effective refractory period (VERP) of hsCLC-3(OE) mice (26.7±1.7ms, n=6) was significantly shorter than that of Clcn3(+/+) mice (36.9±2.8ms, n=8, P<0.05). Under ischemia condition, both VERP (19.8±1.3ms) and atrial effective refractory period (AERP, 34.8±2.5ms) of hsCLC-3(OE) mice were significantly shorter than those of Clcn3(+/+) mice (35.2±3.0ms and 45.8±1.6ms, P<0.01, respectively). Wenckebach atrioventricular nodal block point (AVBP, 91.13±4.08ms) and 2:1 AVBP (71.3±3.8ms) of hsCLC-3(OE) mice were significantly shorter than those of Clcn3(+/+) mice (102.0±2.0ms and 84.1±2.8ms, P<0.05, respectively). However, no differences of ICEP parameters between hsCLC-3(OE) and Clcn3(+/+) mice were observed under reperfusion conditions. CONCLUSION Heart-specific overexpression of hsCLC-3 limited the ischemia-induced QT and ERP prolongation and postponed the advancements of Wenckebach and 2:1 AVBP. CLC-3 up-regulation may serve as an important adaptive mechanism against myocardial ischemia.
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Affiliation(s)
- Ying Yu
- Department of Cardiology, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200092, China; Laboratory of Cardiovascular Phenomics, University of Nevada School of Medicine, Reno, NV 89557-0318, USA; Department of Pharmacology, University of Nevada School of Medicine, Reno, NV 89557-0318, USA
| | - Linda Ye
- Laboratory of Cardiovascular Phenomics, University of Nevada School of Medicine, Reno, NV 89557-0318, USA; Department of Pharmacology, University of Nevada School of Medicine, Reno, NV 89557-0318, USA
| | - Yi-Gang Li
- Department of Cardiology, Xinhua Hospital, Shanghai Jiaotong University School of Medicine, Shanghai 200092, China.
| | - Dean J Burkin
- Department of Pharmacology, University of Nevada School of Medicine, Reno, NV 89557-0318, USA
| | - Dayue Darrel Duan
- Laboratory of Cardiovascular Phenomics, University of Nevada School of Medicine, Reno, NV 89557-0318, USA; Department of Pharmacology, University of Nevada School of Medicine, Reno, NV 89557-0318, USA.
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Stauber T, Weinert S, Jentsch TJ. Cell biology and physiology of CLC chloride channels and transporters. Compr Physiol 2013; 2:1701-44. [PMID: 23723021 DOI: 10.1002/cphy.c110038] [Citation(s) in RCA: 112] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Proteins of the CLC gene family assemble to homo- or sometimes heterodimers and either function as Cl(-) channels or as Cl(-)/H(+)-exchangers. CLC proteins are present in all phyla. Detailed structural information is available from crystal structures of bacterial and algal CLCs. Mammals express nine CLC genes, four of which encode Cl(-) channels and five 2Cl(-)/H(+)-exchangers. Two accessory β-subunits are known: (1) barttin and (2) Ostm1. ClC-Ka and ClC-Kb Cl(-) channels need barttin, whereas Ostm1 is required for the function of the lysosomal ClC-7 2Cl(-)/H(+)-exchanger. ClC-1, -2, -Ka and -Kb Cl(-) channels reside in the plasma membrane and function in the control of electrical excitability of muscles or neurons, in extra- and intracellular ion homeostasis, and in transepithelial transport. The mainly endosomal/lysosomal Cl(-)/H(+)-exchangers ClC-3 to ClC-7 may facilitate vesicular acidification by shunting currents of proton pumps and increase vesicular Cl(-) concentration. ClC-3 is also present on synaptic vesicles, whereas ClC-4 and -5 can reach the plasma membrane to some extent. ClC-7/Ostm1 is coinserted with the vesicular H(+)-ATPase into the acid-secreting ruffled border membrane of osteoclasts. Mice or humans lacking ClC-7 or Ostm1 display osteopetrosis and lysosomal storage disease. Disruption of the endosomal ClC-5 Cl(-)/H(+)-exchanger leads to proteinuria and Dent's disease. Mouse models in which ClC-5 or ClC-7 is converted to uncoupled Cl(-) conductors suggest an important role of vesicular Cl(-) accumulation in these pathologies. The important functions of CLC Cl(-) channels were also revealed by human diseases and mouse models, with phenotypes including myotonia, renal loss of salt and water, deafness, blindness, leukodystrophy, and male infertility.
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Affiliation(s)
- Tobias Stauber
- Leibniz-Institut für Molekulare Pharmakologie FMP and Max-Delbrück-Centrum für Molekulare Medizin MDC, Berlin, Germany
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Abstract
Forward genetic studies have identified several chloride (Cl-) channel genes, including CFTR, ClC-2, ClC-3, CLCA, Bestrophin, and Ano1, in the heart. Recent reverse genetic studies using gene targeting and transgenic techniques to delineate the functional role of cardiac Cl- channels have shown that Cl- channels may contribute to cardiac arrhythmogenesis, myocardial hypertrophy and heart failure, and cardioprotection against ischemia reperfusion. The study of physiological or pathophysiological phenotypes of cardiac Cl- channels, however, is complicated by the compensatory changes in the animals in response to the targeted genetic manipulation. Alternatively, tissue-specific conditional or inducible knockout or knockin animal models may be more valuable in the phenotypic studies of specific Cl- channels by limiting the effect of compensation on the phenotype. The integrated function of Cl- channels may involve multiprotein complexes of the Cl- channel subproteome. Similar phenotypes can be attained from alternative protein pathways within cellular networks, which are influenced by genetic and environmental factors. The phenomics approach, which characterizes phenotypes as a whole phenome and systematically studies the molecular changes that give rise to particular phenotypes achieved by modifying the genotype under the scope of genome/proteome/phenome, may provide more complete understanding of the integrated function of each cardiac Cl- channel in the context of health and disease.
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Affiliation(s)
- Dayue Darrel Duan
- The Laboratory of Cardiovascular Phenomics, Department of Pharmacology, University of Nevada, School of Medicine, Reno, Nevada, USA.
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Mao J, Yuan J, Wang L, Zhang H, Jin X, Zhu J, Li H, Xu B, Chen L. Tamoxifen inhibits migration of estrogen receptor-negative hepatocellular carcinoma cells by blocking the swelling-activated chloride current. J Cell Physiol 2013; 228:991-1001. [PMID: 23042559 DOI: 10.1002/jcp.24245] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Accepted: 09/26/2012] [Indexed: 02/04/2023]
Abstract
Tamoxifen is a triphenylethylene non-steroidal antiestrogen anticancer agent. It also shows inhibitory effects on metastasis of estrogen receptor (EsR)-independent tumors, but the underlying mechanism is unclear. It was demonstrated in this study that, in EsR-negative and highly metastatic human hepatocellular carcinoma MHCC97H cells, tamoxifen-inhibited cell migration, volume-activated Cl(-) currents (I(Cl,vol)) and regulatory volume decrease (RVD) in a concentration-dependent manner with a similar IC(50). Analysis of the relationships between migration, I(Cl,vol) and RVD showed that cell migration was positively correlated with I(Cl,vol) and RVD. Knockdown of the expression of ClC-3 Cl(-) channel proteins by ClC-3 shRNA or siRNA inhibited I(Cl,vol), and cell migration, and these inhibitory effects could not be increased further by addition of tamoxifen in the medium. The results suggest that knockdown of ClC-3 expression may deplete the effects of tamoxifen; tamoxifen may inhibit cell migration by modulating I(Cl,vol) and cell volume. Moreover, tamoxifen decreased the activity of protein kinase C (PKC) and the effects were reversed by the PKC activator PMA. Activation of PKC by PMA could competitively downregulate the inhibitory effects of tamoxifen on I(Cl,vol). PMA promoted cell migration, and knockdown of ClC-3 expression by ClC-3 siRNA abolished the PMA effect on cell migration. The results suggest that tamoxifen may inhibit I(Cl,vol) by suppressing PKC activation; I(Cl,vol) may be an EsR-independent target for tamoxifen in the anti-metastatic action on cancers, especially on EsR-negative cancers. The finding may have an implication in the clinical use of tamoxifen in the treatments of both EsR-positive and EsR-negative cancers.
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Affiliation(s)
- Jianwen Mao
- Department of Pharmacology and Department of Physiology, Medical College, Jinan University, Guangzhou, China
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Bozeat ND, Xiang SY, Ye LL, Yao TY, Duan ML, Burkin DJ, Lamb FS, Duan DD. Activation of volume regulated chloride channels protects myocardium from ischemia/reperfusion damage in second-window ischemic preconditioning. Cell Physiol Biochem 2011; 28:1265-78. [PMID: 22179014 DOI: 10.1159/000335858] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/09/2011] [Indexed: 02/03/2023] Open
Abstract
Activation of volume regulated chloride channels (VRCCs) has been shown to be cardioprotective in ischemic preconditioning (IPC) of isolated hearts but the underlying molecular mechanisms remain unclear. Recent independent studies support that ClC-3, a ClC voltage-gated chloride channel, may function as a key component of the VRCCs. Thus, ClC-3 knockout (Clcn3(-/-)) mice and their age-matched heterozygous (Clcn3(+/-)) and wild-type (Clcn3(+/+)) littermates were used to test whether activation of VRCCs contributes to cardioprotection in early and/or second-window IPC. Targeted disruption of ClC-3 gene caused a decrease in the body weight but no changes in heart/body weight ratio. Telemetry ECG and echocardiography revealed no differences in ECG and cardiac function under resting conditions among all groups. Under treadmill stress (10 m/min for 10 min), the Clcn3(-/-) mice had significant slower heart rate (648±12 bpm) than Clcn3(+/+) littermates (737±19 bpm, n=6, P<0.05). Ex vivo IPC in the isolated working-heart preparations protected cardiac function during reperfusion and significantly decreased apoptosis and infarct size in all groups. In vivo early IPC significantly reduced infarct size in all groups including Clcn3(-/-) mice (22.7±3.7% vs control 40.1±4.3%, n=22, P=0.004). Second-window IPC significantly reduced apoptosis and infarction in Clcn3(+/+) (22.9±3.2% vs 45.7±5.4%, n=22, P<0.001) and Clcn3(+/-) mice (27.5±4.1% vs 42.2±5.7%, n=15, P<0.05) but not in Clcn3(-/-) littermates (39.8±4.9% vs 41.5±8.2%, n=13, P>0.05). Impaired cell volume regulation of the Clcn3(-/-) myocytes may contribute to the failure of cardioprotection by second-window IPC. These results strongly support that activation of VRCCs may play an important cardioprotective role in second-window IPC.
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Affiliation(s)
- Nathan D Bozeat
- Department of Pharmacology, University of Nevada School of Medicine, Reno, Nevada 89557-0318, USA
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Abstract
ClC-3 is a member of the ClC voltage-gated chloride (Cl(-)) channel superfamily. Recent studies have demonstrated the abundant expression and pleiotropy of ClC-3 in cardiac atrial and ventricular myocytes, vascular smooth muscle cells, and endothelial cells. ClC-3 Cl(-) channels can be activated by increase in cell volume, direct stretch of β1-integrin through focal adhesion kinase and many active molecules or growth factors including angiotensin II and endothelin-1-mediated signaling pathways, Ca(2+)/calmodulin-dependent protein kinase II and reactive oxygen species. ClC-3 may function as a key component of the volume-regulated Cl(-) channels, a superoxide anion transport and/or NADPH oxidase interaction partner, and a regulator of many other transporters. ClC-3 has been implicated in the regulation of electrical activity, cell volume, proliferation, differentiation, migration, apoptosis and intracellular pH. This review will highlight the major findings and recent advances in the study of ClC-3 Cl(-) channels in the cardiovascular system and discuss their important roles in cardiac and vascular remodeling during hypertension, myocardial hypertrophy, ischemia/reperfusion, and heart failure.
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Cuddapah VA, Sontheimer H. Ion channels and transporters [corrected] in cancer. 2. Ion channels and the control of cancer cell migration. Am J Physiol Cell Physiol 2011; 301:C541-9. [PMID: 21543740 DOI: 10.1152/ajpcell.00102.2011] [Citation(s) in RCA: 130] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
A hallmark of high-grade cancers is the ability of malignant cells to invade unaffected tissue and spread disease. This is particularly apparent in gliomas, the most common and lethal type of primary brain cancer affecting adults. Migrating cells encounter restricted spaces and appear able to adjust their shape to accommodate to narrow extracellular spaces. A growing body of work suggests that cell migration/invasion is facilitated by ion channels and transporters. The emerging concept is that K(+) and Cl(-) function as osmotically active ions, which cross the plasma membrane in concert with obligated water thereby adjusting a cell's shape and volume. In glioma cells Na(+)-K(+)-Cl(-) cotransporters (NKCC1) actively accumulate K(+) and Cl(-), establishing a gradient for KCl efflux. Ca(2+)-activated K(+) channels and voltage-gated Cl(-) channels are largely responsible for effluxing KCl promoting hydrodynamic volume changes. In other cancers, different K(+) or even Na(+) channels may function in concert with a variety of Cl(-) channels to support similar volume changes. Channels involved in migration are frequently regulated by Ca(2+) signaling, most likely coupling extracellular stimuli to cell migration. Importantly, the inhibition of ion channels and transporters appears to be clinically relevant for the treatment of cancer. Recent preclinical data indicates that inhibition of NKCC1 with an FDA-approved drug decreases neoplastic migration. Additionally, ongoing clinical trials demonstrate that an inhibitor of chloride channels may be a therapy for the treatment of gliomas. Data reviewed here strongly indicate that ion channels are a promising target for the development of novel therapeutics to combat cancer.
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Affiliation(s)
- Vishnu Anand Cuddapah
- Department of Neurobiology and Center for Glial Biology in Medicine, University of Alabama at Birmingham, USA
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CLC-3 chloride channels in the pulmonary vasculature. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 661:237-47. [PMID: 20204734 DOI: 10.1007/978-1-60761-500-2_15] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/24/2023]
Abstract
Volume-sensitive outwardly rectifying anion channels (VSOACs) are expressed in pulmonary artery smooth muscle cells (PASMCs) and have been implicated in cell proliferation, growth, apoptosis and protection against oxidative stress. In this chapter, we review the properties of native VSOACs in PASMCs, and consider the evidence that ClC-3, a member of the ClC superfamily of voltage dependent Cl- channels, may be responsible for native VSOACs in PASMCs. Finally, we examine whether or not native VSOACs and heterologously expressed ClC-3 channels function as bona fide chloride channels or as chloride/proton antiporters.
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Cuddapah VA, Sontheimer H. Molecular interaction and functional regulation of ClC-3 by Ca2+/calmodulin-dependent protein kinase II (CaMKII) in human malignant glioma. J Biol Chem 2010; 285:11188-96. [PMID: 20139089 DOI: 10.1074/jbc.m109.097675] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Glioblastoma multiforme is the most common and lethal primary brain cancer in adults. Tumor cells diffusely infiltrate the brain making focal surgical and radiation treatment challenging. The invasion of glioma cells into normal brain is facilitated by the activity of ion channels aiding dynamic regulation of cell volume. Recent studies have specifically implicated ClC-3, a voltage-gated chloride channel, in this process. However, the interaction between ClC-3 activity and cell movement is poorly understood. Here, we demonstrate that ClC-3 is highly expressed on the plasma membrane of human glioma cells where its activity is regulated through phosphorylation via Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). Intracellular infusion of autoactivated CaMKII via patch pipette enhanced chloride currents 3-fold, and this regulation was inhibited by autocamtide-2 related inhibitory peptide, a CaMKII-specific inhibitor. CaMKII modulation of chloride currents was also lost upon stable small hairpin RNA knockdown of ClC-3 channels indicating a specific interaction of ClC-3 and CaMKII. In ClC-3-expressing cells, inhibition of CaMKII reduced glioma invasion to the same extent as direct inhibition of ClC-3. The importance of the molecular interaction of ClC-3 and CaMKII is further supported by our finding that CaMKII co-localizes and co-immunoprecipitates with ClC-3. ClC-3 and CaMKII also co-immunoprecipitate in tissue biopsies from patients diagnosed with grade IV glioblastoma. These tumor samples show 10-fold higher ClC-3 protein expression than nonmalignant brain. These data suggest that CaMKII is a molecular link translating intracellular calcium changes, which are intrinsically associated with glioma migration, to changes in ClC-3 conductance required for cell movement.
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Affiliation(s)
- Vishnu Anand Cuddapah
- Department of Neurobiology and Center for Glial Biology in Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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Wangemann P, Kim HM, Billings S, Nakaya K, Li X, Singh R, Sharlin DS, Forrest D, Marcus DC, Fong P. Developmental delays consistent with cochlear hypothyroidism contribute to failure to develop hearing in mice lacking Slc26a4/pendrin expression. Am J Physiol Renal Physiol 2009; 297:F1435-47. [PMID: 19692489 PMCID: PMC2781347 DOI: 10.1152/ajprenal.00011.2009] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2009] [Accepted: 08/13/2009] [Indexed: 02/08/2023] Open
Abstract
Mutations of SLC26A4 cause an enlarged vestibular aqueduct, nonsyndromic deafness, and deafness as part of Pendred syndrome. SLC26A4 encodes pendrin, an anion exchanger located in the cochlea, thyroid, and kidney. The goal of the present study was to determine whether developmental delays, possibly mediated by systemic or local hypothyroidism, contribute to the failure to develop hearing in mice lacking Slc26a4 (Slc26a4(-/-)). We evaluated thyroid function by voltage and pH measurements, by array-assisted gene expression analysis, and by determination of plasma thyroxine levels. Cochlear development was evaluated for signs of hypothyroidism by microscopy, in situ hybridization, and quantitative RT-PCR. No differences in plasma thyroxine levels were found in Slc26a4(-/-) and sex-matched Slc26a4(+/-) littermates between postnatal day 5 (P5) and P90. In adult Slc26a4(-/-) mice, the transepithelial potential and the pH of thyroid follicles were reduced. No differences in the expression of genes that participate in thyroid hormone synthesis or ion transport were observed at P15, when plasma thyroxine levels peaked. Scala media of the cochlea was 10-fold enlarged, bulging into and thereby displacing fibrocytes, which express Dio2 to generate a cochlear thyroid hormone peak at P7. Cochlear development, including tunnel opening, arrival of efferent innervation at outer hair cells, endochondral and intramembraneous ossification, and developmental changes in the expression of Dio2, Dio3, and Tectb were delayed by 1-4 days. These data suggest that pendrin functions as a HCO3- transporter in the thyroid, that Slc26a4(-/-) mice are systemically euthyroid, and that delays in cochlear development, possibly due to local hypothyroidism, lead to the failure to develop hearing.
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Affiliation(s)
- Philine Wangemann
- Anatomy and Physiology Department, Kansas State University, Manhattan, KS 66506, USA.
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Cardiac-specific, inducible ClC-3 gene deletion eliminates native volume-sensitive chloride channels and produces myocardial hypertrophy in adult mice. J Mol Cell Cardiol 2009; 48:211-9. [PMID: 19615374 DOI: 10.1016/j.yjmcc.2009.07.003] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2009] [Revised: 06/19/2009] [Accepted: 07/06/2009] [Indexed: 11/24/2022]
Abstract
Native volume-sensitive outwardly rectifying anion channels (VSOACs) play a significant role in cell volume homeostasis in mammalian cells. However, the molecular correlate of VSOACs has been elusive to identify. The short isoform of ClC-3 (sClC-3) is a member of the mammalian ClC gene family and has been proposed to be a molecular candidate for VSOACs in cardiac myocytes and vascular smooth muscle cells. To directly test this hypothesis, and assess the physiological role of ClC-3 in cardiac function, we generated a novel line of cardiac-specific inducible ClC-3 knock-out mice. These transgenic mice were maintained on a doxycycline diet to preserve ClC-3 expression; removal of doxycycline activates Cre recombinase to inactivate the Clcn3 gene. Echocardiography revealed dramatically reduced ejection fraction and fractional shortening, and severe signs of myocardial hypertrophy and heart failure in the knock-out mice at both 1.5 and 3 weeks off doxycycline. In mice off doxycycline, time-dependent inactivation of ClC-3 gene expression was confirmed in atrial and ventricular cells by qRT-PCR and Western blot analysis. Electrophysiological examination of native VSOACs in isolated atrial and ventricular myocytes 3 weeks off doxycycline revealed a complete elimination of the currents, whereas at 1.5 weeks, VSOAC current densities were significantly reduced, compared to age-matched control mice maintained on doxycycline. These results indicate that ClC-3 is a key component of native VSOACs in mammalian heart and plays a significant cardioprotective role against cardiac hypertrophy and failure.
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