Figure 3.

Outer hair cell dysfunction and reduced amplitude of auditory brainstem response (ABR) peak I in a transgenic mouse strain that robustly overexpresses the mitochondrial 12S ribosomal RNA methyltransferase TFB1M (Tg-mtTFB1). A: Hair cell counts in wild-type (WT; gray bars) and Tg-mtTFB1 (Tg-B1; black bars) mice. Cells counted are as indicated: inner hair cells (IHCs), outer hair cell rows 1 (OHC1), 2 (OHC2), and 3 (OHC3). B: Nonlinear capacitance (NLC) recordings from OHCs isolated from WT (closed squares) and Tg-B1 (open circles) mice. The voltage at peak capacitance (V_h) is plotted, and means were compared with a t-test. There is a statistically significant change in Tg-mtTFB1 [t₍₁₁₎ = 2.3]. Other parameters of NLC were not different (means ± SD): maximum nonlinear charge moved (pC), 0.54 ± 0.11 WT/0.42 ± 0.11 Tg-mtTFB1; z, 0.76 ± 0.05 WT/0.76 ± 0.07 Tg-mtTFB1; linear membrane capacitance (pF), 4.93 ± 0.47 WT/4.44 ± 0.72 Tg-mtTFB1. The amplitude of ABR peak I was measured at 8 kHz at the indicated intensities (decibels sound pressure level). Suprathreshold for 9- to 12-month-old mice (C) and 3- to 6-month-old mice (D). Suprathresholds at 9 to 12 months in Tg-mtTFB1 mice are significantly lower than WT controls by two-way analysis of variance. ^∗P < 0.05.