title: Identification of ClC-2 and CIC-K2 chloride channels in cultured rat type IV spiral ligament fibrocytes.
abstract: Voltage-gated chloride channels (ClCs) are important mediators of cellular ion homeostasis and volume regulation. In an earlier study, we used immunohistochemical, Western blot, and reverse transcriptase PCR (RT-PCR) approaches to identify ClC-K variants in types II, IV, and V fibrocytes of the rodent spiral ligament. We have now confirmed the expression of ClC-K2 in these cells by in situ hybridization. All three of these fibrocyte subtypes are thought to be involved in cochlear K(+) recycling; thus, it is important to understand the precise mechanisms regulating their membrane conductance and the role played by ClCs in this process. In this study, we report the characterization of a secondary cell line derived from explants from the region of the rat spiral ligament underlying and inferior to the spiral prominence. The cultured cells were immunopositive for vimentin, Na,K/ATPase, Na,K,Cl-cotransporter, carbonic anhydrase isozyme II, and creatine kinase isozyme BB, but not for cytokeratins or Ca/ATPase, an immunostaining profile indicative of the type IV subtype. Evaluation of the cultures by RT-PCR and Western blot analysis confirmed the presence of both ClC-2 and -K2. Whole-cell patch clamp recordings identified two biophysically distinct Cl(-) currents in the cultured cells. One, an inwardly rectifying Cl(-) current activated by hyperpolarization or decreasing extracellular pH corresponded with the properties of ClC-2. The other, a weak outwardly rectifying Cl(-) current regulated by extracellular pH, Cl(-), and Ca(2+) resembled the channel characteristics of ClC-K2 when expressed in Xenopus oocytes. These findings suggest that at least two functionally different chloride channels are involved in regulating membrane anion conductance in cultured type IV spiral ligament fibrocytes.
authors.affiliation: Department of Pathology and Laboratory Medicine, Medical University of South Carolina, Charleston, SC 29425, USA.
authors.forename: Chunyan
authors.initials: C
authors.lastname: Qu
authors.forename: Fenghe
authors.initials: F
authors.lastname: Liang
authors.forename: Nancy M
authors.initials: NM
authors.lastname: Smythe
authors.forename: Bradley A
authors.initials: BA
authors.lastname: Schulte
mesh_terms: D000818:Animals; D027321:Anion Transport Proteins / Q000032:analysis* / Q000235:genetics; D000090007:CLC-2 Chloride Channels; D002478:Cells, Cultured; D018118:Chloride Channels / Q000032:analysis* / Q000235:genetics; D003051:Cochlea / Q000737:chemistry* / Q000166:cytology*; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000032:analysis* / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D027321:Anion Transport Proteins; D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels; C486572:Clcnkb protein, rat; D008565:Membrane Proteins; D012333:RNA, Messenger