Functional IsK/KvLQT1 potassium channel in a new corticosteroid-sensitive cell line derived from the inner ear.
Endolymph, a high K(+)/low Na(+) fluid, participates in mechanoelectrical transduction in inner ear. Molecular mechanisms controlling endolymph ion homeostasis remain elusive, hampered by the lack of appropriate cellular models. We established an inner ear cell line by targeted oncogenesis. The expression of SV40 T antigen was driven by the proximal promoter of the human mineralocorticoid receptor (MR) gene, a receptor expressed in the inner ear. The EC5v cell line, microdissected from the semicircular canal, grew as a monolayer of immortalized epithelial cells forming domes. EC5v cells exhibited on filters of high transepithelial resistance and promoted K(+) secretion and Na(+) absorption. Functional MR and the 11beta-hydroxysteroid dehydrogenase type 2, a key enzyme responsible for MR selectivity were identified. Expression of the epithelial sodium channel and serum glucocorticoid-regulated kinase 1 was shown to be up-regulated by aldosterone, indicating that EC5v represents a novel corticosteroid-sensitive cell line. Ionic measurements and (86)Rb transport assays revealed an apical secretion of K(+) at least in part through the I(sK)/KvLQT1 potassium channel under standard culture conditions. However, when cells were exposed to high apically K(+)/low Na(+) fluid, mimicking endolymph exposure, I(sK)/KvLQT1 actually functioned as a strict apical to basolateral K(+) channel inhibited by clofilium. Quantitative reverse transcriptase-PCR further demonstrated that expression of KvLQT1 but not of I(sK) was down-regulated by high K(+) concentration. This first vestibular cellular model thus constitutes a valuable system to further investigate the molecular mechanisms controlling ionic transports in the inner ear and the pathophysiological consequences of their dysfunctions in vertigo and hearing loss.
INSERM EMI-U 0112, Faculté de Médecine Xavier Bichat, Université Paris 7, 16 rue Henri Huchard, 75870 Paris cedex 18, France.
Marie
M
Teixeira
Say
S
Viengchareun
Daniel
D
Butlen
Chrystophe
C
Ferreira
Françoise
F
Cluzeaud
Marcel
M
Blot-Chabaud
Marc
M
Lombès
Evelyne
E
Ferrary
D042842:11-beta-Hydroxysteroid Dehydrogenases / Q000378:metabolism; D000305:Adrenal Cortex Hormones / Q000378:metabolism*; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism; D001692:Biological Transport; D015153:Blotting, Western; D002384:Catalysis; D018929:Cell Culture Techniques / Q000379:methods*; D002460:Cell Line; D002478:Cells, Cultured; D017931:DNA Primers / Q000737:chemistry; D007758:Ear, Inner / Q000166:cytology* / Q000378:metabolism; D004710:Endolymph / Q000378:metabolism; D007150:Immunohistochemistry; D007477:Ions; D051657:KCNQ1 Potassium Channel / Q000378:metabolism / Q000502:physiology*; D007700:Kinetics; D051379:Mice; D008822:Mice, Transgenic; D008854:Microscopy, Electron; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D011188:Potassium / Q000737:chemistry / Q000378:metabolism; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism / Q000502:physiology*; D011485:Protein Binding; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000737:chemistry; D013997:Time Factors; D019076:Transgenes
D000305:Adrenal Cortex Hormones; D000952:Antigens, Polyomavirus Transforming; D017931:DNA Primers; D007477:Ions; D051657:KCNQ1 Potassium Channel; C092068:Kcne1 protein, mouse; C496910:Kcnq1 protein, mouse; D024642:Potassium Channels, Voltage-Gated; D000644:Quaternary Ammonium Compounds; D012333:RNA, Messenger; C022799:clofilium; D012964:Sodium; D042842:11-beta-Hydroxysteroid Dehydrogenases; D011188:Potassium