Functional analysis of ionic channel and transporter of the cochlear marginal cell using cellular physiology and molecular biology

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A variety of ionic channels and transportes are known to be related to inner ear function. We have so far found Cl voltage-dependent chloride channels (ClC), Na-K-2C1 cotransporter (CCC), and Na-Ca exchanger (NCX), and Na-H exchange (NHE) in the cochlea by physiological methods. Furthermore, recent advances in molecular biology enabled us to prove the definite evidence of molecular characterization of these ion chanells and transportes. We used the reverse transcription-polymerase chain reaction (RT-PCR) to assess the expression of various isoforms and the non-radioactive in situ hybridization (ISH) to examine their localization. Among CIC family, ClC-2 and -3 were significantly present in the inner ear tissue. BSC2 transcript alone was detected in the cochlea and intensively located in the strial marginal cells and spiral ligament fibrocytes, indicating a good explanation of loop-diuretics cochleotoxicity. All of three isoforms of NCX (1-3) were detected in the inner ear. Unique spicing varients of NCX-1 were found in the cochlear modiolus. Although NHE-2, -3, and -4 isoform mRNAs could be detected in the cochlear tissue, NHE-1 message was clearly dominant. NHE-1 isoform expression was distributed in the hair cells, marginal cells, and spiral ligament fibrocytes, and ganglion cells.