Department of Biomedical Science, University of Sheffield, Sheffield S10 2TN, United Kingdom.
J Neurosci. 2012 Aug 1;32(31):10479-83. doi: 10.1523/JNEUROSCI.0803-12.2012.
Spontaneous Ca(2+)-dependent electrical activity in the immature mammalian cochlea is thought to instruct the formation of the tonotopic map during the differentiation of sensory hair cells and the auditory pathway. This activity occurs in inner hair cells (IHCs) during the first postnatal week, and the pattern differs along the cochlea. During the second postnatal week, which is before the onset of hearing in most rodents, the resting membrane potential for IHCs is apparently more hyperpolarized (approximately -75 mV), and it remains unclear whether spontaneous action potentials continue to occur. We found that when mouse IHC hair bundles were exposed to the estimated in vivo endolymphatic Ca(2+) concentration (0.3 mm) present in the immature cochlea, the increased open probability of the mechanotransducer channels caused the cells to depolarize to around the action potential threshold (approximately -55 mV). We propose that, in vivo, spontaneous Ca(2+) action potentials are intrinsically generated by IHCs up to the onset of hearing and that they are likely to influence the final sensory-independent refinement of the developing cochlea.
在感觉毛细胞和听觉通路分化过程中，人们认为未成熟哺乳动物耳蜗中的自发 Ca(2+)-依赖性电活动指导了音位图谱的形成。这种活动发生在出生后第一周的内毛细胞 (IHC) 中，并且在耳蜗中沿不同的模式发生。在大多数啮齿动物听力开始之前的第二周，IHC 的静息膜电位显然更超极化（约为-75 mV），目前尚不清楚是否会继续发生自发动作电位。我们发现，当将小鼠 IHC 毛束暴露于估计在体内存在的内淋巴液 Ca(2+)浓度（0.3 mm）时，机械转导通道的开放概率增加会导致细胞去极化至动作电位阈值附近（约为-55 mV）。我们提出，在体内，自发的 Ca(2+) 动作电位是由 IHC 产生的，直到听力开始，并且它们可能会影响发育中的耳蜗的最终感觉独立的细化。
