title: Protection of the cochlear hair cells in adult C57BL/6J mice by T-type calcium channel blockers.
abstract: The aim of the present study was to investigate the protective effect of T-type calcium channel blockers against presbycusis, using a C57BL/6J mice model. The expression of three T-type calcium channel receptor subunits in the cochlea of 6-8-week-old C57BL/6J mice was evaluated using reverse transcription-quantitative polymerase chain reaction. The results confirmed that the three subunits were expressed in the cochlea. In addition, the capacity of T-type calcium channel blockers to protect the cochlear hair cells of 24-26-week-old C57BL/6J mice was investigated in mice treated with mibefradil, benidipine or saline for 4 weeks. Differences in hearing threshold were detected using auditory brainstem recording (ABR), while differences in amplitudes were measured using a distortion product otoacoustic emission (DPOAE) test. The ABR test results showed that the hearing threshold significantly decreased at 24 kHz in the mibefradil-treated and benidipine-treated groups compared with the saline-treated group. The DPOAE amplitudes in the mibefradil-treated group were increased compared with those in the saline-treated group at the F2 frequencies of 11.3 and 13.4 kHz. Furthermore, the DPOAE amplitudes in the benidipine-treated group were increased compared with those in the saline-treated group at an F2 frequency of 13.4 kHz. The loss of outer hair cells (OHCs) was not evident in the mibefradil-treated group; however, the stereocilia of the inner hair cells (IHCs) were disorganised and sparse. In summary, these results indicate that the administration of a T-type calcium channel blocker for four consecutive weeks may improve the hearing at 24 kHz of 24-26-week-old C57BL/6J mice. The function and morphology of the OHCs of the C57BL/6J mice were significantly altered by the administration of a T-type calcium channel blocker; however, the IHCs were unaffected.
authors.affiliation: Department of Otolaryngology, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215006, P.R. China.
authors.forename: Ya-Feng
authors.initials: YF
authors.lastname: Yu
authors.affiliation: Department of Otolaryngology, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215006, P.R. China.
authors.forename: Wen-Ying
authors.initials: WY
authors.lastname: Wu
authors.affiliation: Department of Otolaryngology, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215006, P.R. China.
authors.forename: Gen-Sheng
authors.initials: GS
authors.lastname: Xiao
authors.affiliation: Department of Otolaryngology, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215006, P.R. China.
authors.forename: Hong-Yang
authors.initials: HY
authors.lastname: Ling
authors.affiliation: Department of Otolaryngology, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215006, P.R. China.
authors.forename: Chen
authors.initials: C
authors.lastname: Pan
keywords: T-type calcium channel; calcium channel blocker; hair cell; receptor