Brandt Andreas, Striessnig Joerg, Moser Tobias
Department of Otolaryngology, Goettingen University Medical School, 37075 Goettingen, Germany.
J Neurosci. 2003 Nov 26;23(34):10832-40. doi: 10.1523/JNEUROSCI.23-34-10832.2003.
Cochlear inner hair cells (IHCs) release neurotransmitter onto afferent auditory nerve fibers in response to sound stimulation. During early development, afferent synaptic transmission is triggered by spontaneous Ca2+ spikes of IHCs, which are under efferent cholinergic control. Around the onset of hearing, large-conductance Ca2+-activated K+ channels are acquired, and Ca2+ spikes as well as the cholinergic innervation are lost. Here, we performed patch-clamp measurements in IHCs of mice lacking the CaV1.3 channel (CaV1.3-/-) to investigate the role of this prevailing voltage-gated Ca2+ channel in IHC development and synaptic function. The small Ca2+ current remaining in IHCs from 3-week-old CaV1.3-/- mice was mainly mediated by L-type Ca2+ channels, because it was sensitive to dihydropyridines but resistant to inhibitors of non-L-type Ca2+ channels such as omega-conotoxins GVIA and MVIIC and SNX-482. Depolarization induced only marginal exocytosis in CaV1.3-/- IHC, which was solely mediated by L-type Ca2+ channels, whereas robust exocytic responses were elicited by photolysis of caged Ca2+. Secretion triggered by short depolarizations was reduced proportionally to the Ca2+ current, suggesting that the coupling of the remaining channels to exocytosis was unchanged. CaV1.3-/- IHCs lacked the Ca2+ action potentials and displayed a complex developmental failure. Most strikingly, we observed a continued presence of efferent cholinergic synaptic transmission and a lack of functional large-conductance Ca2+-activated K+ channels up to 4 weeks after birth. We conclude that CaV1.3 channels are essential for normal hair cell development and synaptic transmission.
耳蜗内毛细胞（IHCs）在受到声音刺激时会向传入听觉神经纤维释放神经递质。在早期发育过程中，传入突触传递由IHCs的自发性Ca2+尖峰触发，而这些尖峰受传出胆碱能控制。在听力开始时左右，大电导Ca2+激活K+通道出现，Ca2+尖峰以及胆碱能神经支配消失。在此，我们对缺乏CaV1.3通道（CaV1.3-/-）的小鼠的IHCs进行了膜片钳测量，以研究这种主要的电压门控Ca2+通道在IHC发育和突触功能中的作用。3周龄CaV1.3-/-小鼠的IHCs中剩余的小Ca2+电流主要由L型Ca2+通道介导，因为它对二氢吡啶敏感，但对非L型Ca2+通道抑制剂如ω-芋螺毒素GVIA、MVIIC和SNX-482有抗性。去极化仅在CaV1.3-/- IHC中诱导了少量的胞吐作用，这完全由L型Ca2+通道介导，而通过光解笼锁Ca2+引发了强烈的胞吐反应。短时间去极化触发的分泌与Ca2+电流成比例减少，表明剩余通道与胞吐作用的偶联未改变。CaV1.3-/- IHCs缺乏Ca2+动作电位，并表现出复杂的发育失败。最引人注目的是，我们观察到在出生后4周内，传出胆碱能突触传递持续存在，且缺乏功能性大电导Ca2+激活K+通道。我们得出结论，CaV1.3通道对于正常毛细胞发育和突触传递至关重要。
