Chen Guang-Di, Zhao Hong-Bo
Center for Hearing and Deafness, 137 Cary Hall, 3435 Main Street, SUNY at Buffalo, Buffalo, NY 14214, USA.
Hear Res. 2007 Apr;226(1-2):14-21. doi: 10.1016/j.heares.2006.06.007. Epub 2006 Jul 25.
Outer hair cells (OHCs) play an important role in cochlear amplification via their length changes (electromotility). A noise-induced cochlear amplification loss leading to a permanent threshold shift (PTS) was observed without a significant hair cell loss in rats [Chen, G.D., Liu, Y., 2005. Mechanisms of noise-induced hearing loss potentiation by hypoxia. Hear. Res. 200, 1-9.]. Since motor proteins are inserted in the OHC lateral membrane, any change in the OHC plasma membrane may result in a loss of OHC electromotility, leading to a loss of cochlear amplification. In this study, the lateral diffusion in the OHC plasma membrane was determined in vitro in guinea pigs by fluorescent recovery after photobleaching (FRAP) after an in vivo noise exposure. The lateral diffusion in the OHC plasma membrane demonstrated a length-dependence, which increased as OHC length increased. A reduction in the lateral diffusion was observed in those OHCs with lengths of 50-70 microm after exposure to an 8-kHz octave band noise at 110 dB SPL for 3h. This membrane fluidity change was associated with the selective PTS at frequencies around 8 kHz. The reduction of the lateral diffusion in the OHC lateral wall indicated that noise could impair the micromechanics of the OHC lateral wall and might consequently impair OHC electromotility to induce threshold shift.
外毛细胞（OHCs）通过其长度变化（电运动）在耳蜗放大过程中发挥重要作用。在大鼠中观察到，噪声诱导的耳蜗放大功能丧失导致永久性阈移（PTS），但未出现明显的毛细胞损失[Chen, G.D., Liu, Y., 2005. Mechanisms of noise-induced hearing loss potentiation by hypoxia. Hear. Res. 200, 1-9.]。由于运动蛋白嵌入OHC的外侧膜，OHC质膜的任何变化都可能导致OHC电运动丧失，进而导致耳蜗放大功能丧失。在本研究中，通过体内噪声暴露后光漂白荧光恢复（FRAP）法，在体外测定了豚鼠OHC质膜的侧向扩散。OHC质膜的侧向扩散表现出长度依赖性，随OHC长度增加而增加。在暴露于110 dB SPL的8 kHz倍频程带噪声3小时后，观察到长度为50 - 70微米的OHC的侧向扩散降低。这种膜流动性变化与8 kHz左右频率处的选择性PTS有关。OHC侧壁侧向扩散的降低表明，噪声可能损害OHC侧壁的微力学，进而可能损害OHC的电运动，导致阈移。
