Identification of ClC-2 and CIC-K2 Chloride Channels in Cultured Rat Type IV Spiral Ligament Fibrocytes

ABSTRACT The function of the orphan glutamate receptor delta subunits (GluRδ1 and GluRδ2) remains unclear. GluRδ2 is expressed exclusively in the Purkinje cells of the cerebellum, and GluRδ1 is prominently expressed in inner ear hair cells and neurons of the hippocampus. We found that mice lacking the GluRδ1 protein displayed significant cochlear threshold shifts for frequencies of >16 kHz. These deficits correlated with a substantial loss of type IV spiral ligament fibrocytes and a significant reduction of endolymphatic potential in high-frequency cochlear regions. Vulnerability to acoustic injury was significantly enhanced; however, the efferent innervation of hair cells and the classic efferent inhibition of outer hair cells were unaffected. Hippocampal and vestibular morphology and function were normal. Our findings show that the orphan GluRδ1 plays an essential role in high-frequency hearing and ionic homeostasis in the basal cochlea, and the locus encoding GluRδ1 represents a candidate gene for congenital or acquired high-frequency hearing loss in humans.

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Inhibition of the calcium- and voltage-dependent big conductance potassium channel ameliorates cisplatin-induced apoptosis in spiral ligament fibrocytes of the cochlea

Neuroscience ◽

10.1016/j.neuroscience.2005.05.055 ◽

2005 ◽

Vol 135 (1) ◽

pp. 263-271 ◽

Cited By ~ 37

Author(s):

F. Liang ◽

B.A. Schulte ◽

C. Qu ◽

W. Hu ◽

Z. Shen

Keyword(s):

Potassium Channel ◽

Spiral Ligament ◽

Voltage Dependent ◽

Induced Apoptosis ◽

Spiral Ligament Fibrocytes

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DHHC7-mediated palmitoylation of the accessory protein barttin critically regulates the functions of ClC-K chloride channels

Journal of Biological Chemistry ◽

10.1074/jbc.ra119.011049 ◽

2020 ◽

Vol 295 (18) ◽

pp. 5970-5983 ◽

Cited By ~ 2

Author(s):

Nataliya Gorinski ◽

Daniel Wojciechowski ◽

Daria Guseva ◽

Dalia Abdel Galil ◽

Franziska E. Mueller ◽

...

Keyword(s):

Chloride Channels ◽

Bartter Syndrome ◽

Post Translational Modification ◽

Salt Diet ◽

Type Iv ◽

Low Salt ◽

Accessory Subunit ◽

Palmitoyl Acyltransferase

Barttin is the accessory subunit of the human ClC-K chloride channels, which are expressed in both the kidney and inner ear. Barttin promotes trafficking of the complex it forms with ClC-K to the plasma membrane and is involved in activating this channel. Barttin undergoes post-translational palmitoylation that is essential for its functions, but the enzyme(s) catalyzing this post-translational modification is unknown. Here, we identified zinc finger DHHC-type containing 7 (DHHC7) protein as an important barttin palmitoyl acyltransferase, whose depletion affected barttin palmitoylation and ClC-K-barttin channel activation. We investigated the functional role of barttin palmitoylation in vivo in Zdhhc7−/− mice. Although palmitoylation of barttin in kidneys of Zdhhc7−/− animals was significantly decreased, it did not pathologically alter kidney structure and functions under physiological conditions. However, when Zdhhc7−/− mice were fed a low-salt diet, they developed hyponatremia and mild metabolic alkalosis, symptoms characteristic of human Bartter syndrome (BS) type IV. Of note, we also observed decreased palmitoylation of the disease-causing R8L barttin variant associated with human BS type IV. Our results indicate that dysregulated DHHC7-mediated barttin palmitoylation appears to play an important role in chloride channel dysfunction in certain BS variants, suggesting that targeting DHHC7 activity may offer a potential therapeutic strategy for reducing hypertension.

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A voltage- and Ca2+-dependent big conductance K channel in cochlear spiral ligament fibrocytes

Pflügers Archiv - European Journal of Physiology ◽

10.1007/s00424-002-0976-9 ◽

2003 ◽

Vol 445 (6) ◽

pp. 683-692 ◽

Cited By ~ 13

Author(s):

F. Liang ◽

A. Niedzielski ◽

B. A. Schulte ◽

S. S. Spicer ◽

D. J. Hazen-Martin ◽

...

Keyword(s):

K Channel ◽

Spiral Ligament ◽

Spiral Ligament Fibrocytes

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Spiral ligament fibrocytes release chemokines in response to otitis media pathogens

Acta Oto-Laryngologica ◽

10.1080/00016480500452525 ◽

2006 ◽

Vol 126 (6) ◽

pp. 564-569 ◽

Cited By ~ 39

Author(s):

Sung-Kyun Moon ◽

Raekil Park ◽

Sung-Kyun Moon ◽

Raekil Park ◽

...

Keyword(s):

Otitis Media ◽

Spiral Ligament ◽

Spiral Ligament Fibrocytes

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Generation and analyses of R8L barttin knockin mouse

AJP Renal Physiology ◽

10.1152/ajprenal.00604.2010 ◽

2011 ◽

Vol 301 (2) ◽

pp. F297-F307 ◽

Cited By ~ 36

Author(s):

Naohiro Nomura ◽

Masato Tajima ◽

Noriko Sugawara ◽

Tetsuji Morimoto ◽

Yoshiaki Kondo ◽

...

Keyword(s):

Chloride Channels ◽

Plasma Membranes ◽

Chloride Transport ◽

Mdck Cells ◽

Intracellular Localization ◽

Bartter Syndrome ◽

K Channel ◽

Type Iv ◽

Knockin Mouse

Barttin, a gene product of BSND, is one of four genes responsible for Bartter syndrome. Coexpression of barttin with ClC-K chloride channels dramatically induces the expression of ClC-K current via insertion of ClC-K-barttin complexes into plasma membranes. We previously showed that stably expressed R8L barttin, a disease-causing missense mutant, is retained in the endoplasmic reticulum (ER) of Madin-Darby canine kidney (MDCK) cells, with the barttin β-subunit remaining bound to ClC-K α-subunits (Hayama A, Rai T, Sasaki S, Uchida S. Histochem Cell Biol 119: 485–493, 2003). However, transient expression of R8L barttin in MDCK cells was reported to impair ClC-K channel function without affecting its subcellular localization. To investigate the pathogenesis in vivo, we generated a knockin mouse model of Bartter syndrome that carries the R8L mutation. These mice display disease-like phenotypes (hypokalemia, metabolic alkalosis, and decreased NaCl reabsorption in distal tubules) under a low-salt diet. Immunofluorescence and immunoelectron microscopy revealed that the plasma membrane localization of both R8L barttin and the ClC-K channel was impaired in these mice, and transepithelial chloride transport in the thin ascending limb of Henle's loop (tAL) as well as thiazide-sensitive chloride clearance were significantly reduced. This reduction in transepithelial chloride transport in tAL, which is totally dependent on ClC-K1/barttin, correlated well with the reduction in the amount of R8L barttin localized to plasma membranes. These results suggest that the major cause of Bartter syndrome type IV caused by R8L barttin mutation is its aberrant intracellular localization.

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Immunolocalization of aquaporin CHIP in the guinea pig inner ear

AJP Cell Physiology ◽

10.1152/ajpcell.1995.269.6.c1450 ◽

1995 ◽

Vol 269 (6) ◽

pp. C1450-C1456 ◽

Cited By ~ 55

Author(s):

K. M. Stankovic ◽

J. C. Adams ◽

D. Brown

Keyword(s):

Inner Ear ◽

Basilar Membrane ◽

Polyclonal Antibodies ◽

Close Association ◽

Water Channel ◽

Normal Function ◽

Oval Window ◽

Spiral Ligament ◽

Bony Labyrinth ◽

Spiral Ligament Fibrocytes

Aquaporin CHIP (AQP-CHIP) is a water channel protein previously identified in red blood cells and water transporting epithelia. The inner ear is an organ of hearing and balance whose normal function depends critically on maintenance of fluid homeostasis. In this study, AQP-CHIP, or a close homologue, was found in specific cells of the inner ear, as assessed by immunocytochemistry with the use of affinity-purified polyclonal antibodies against AQP-CHIP.AQP-CHIP was predominantly found in fibrocytes in close association with bone, including most of the cells lining the bony labyrinth and in fibrocytes lining the endolymphatic duct and sac. AQP-CHIP-positive cells not directly apposing bone include cells under the basilar membrane, some type III fibrocytes of the spiral ligament, fibrocytes of the spiral limbus, and the trabecular perilymphatic tissue extending from the membranous to the bony labyrinth. AQP-CHIP was also found in the periosteum of the middle ear and cranial bones, as well as in chondrocytes of the oval window and stapes. The distribution of AQP-CHIP in the inner ear suggests that AQP-CHIP may have special significance for maintenance of bone and the basilar membrane, and for function of the spiral ligament.

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