Department of Otorhinolaryngology, Shanghai Jiao Tong University Affiliated Sixth People's Hospital, 600 Yishan Road, Shanghai, 200233, P. R. China.
Department of Otorhinolaryngology, West China Hospital, Sichuan University, No. 37, GuoXueXiang, Chengdu, 610041, P. R. China.
Sci Rep. 2017 Mar 27;7(1):431. doi: 10.1038/s41598-017-00275-9.
Neonatal brain is particularly vulnerable to pathological levels of bilirubin which elevates and overloads intracellular Ca, leading to neurotoxicity. However, how voltage-gated calcium channels (VGCCs) are functionally involved in excess calcium influx remains unknown. By performing voltage-clamp recordings from bushy cells in the ventral cochlear nucleus (VCN) in postnatal rat pups (P4-17), we found the total calcium current density was more than doubled over P4-17, but the relative weight of VGCC subtypes changed dramatically, being relatively equal among T, L, N, P/Q and R-type at P4-6 to predominantly L, N, R over T and P/Q at P15-17. Surprisingly, acute administration of bilirubin augmented the VGCC currents specifically mediated by high voltage-activated (HVA) P/Q-type calcium currents. This augment was attenuated by intracellular loading of Ca buffer EGTA or calmodulin inhibitory peptide. Our findings indicate that acute exposure to bilirubin increases VGCC currents, primarily by targeting P/Q-type calcium channels via Ca and calmodulin dependent mechanisms to overwhelm neurons with excessive Ca. Since P/Q-subtype calcium channels are more prominent in neonatal neurons (e.g. P4-6) than later stages, we suggest this subtype-specific enhancement of P/Q-type Ca currents likely contributes to the early neuronal vulnerability to hyperbilirubinemia in auditory and other brain regions.
新生儿大脑特别容易受到胆红素的病理性水平的影响，胆红素会升高并使细胞内钙超载，导致神经毒性。然而，电压门控钙通道（VGCCs）如何在过量钙内流中发挥功能尚不清楚。通过在出生后大鼠幼崽（P4-17）的耳蜗腹核（VCN）中的丛状细胞上进行电压钳记录，我们发现总钙电流密度在 P4-17 期间增加了一倍以上，但 VGCC 亚型的相对权重发生了显著变化，在 P4-6 时 T、L、N、P/Q 和 R 型之间相对相等，而在 P15-17 时则主要是 L、N、R 型相对于 T 和 P/Q 型。令人惊讶的是，胆红素的急性给药特异性地增强了由高电压激活（HVA）P/Q 型钙电流介导的 VGCC 电流。这种增强作用被细胞内钙缓冲剂 EGTA 或钙调蛋白抑制肽的负载所减弱。我们的发现表明，急性暴露于胆红素会增加 VGCC 电流，主要是通过钙和钙调蛋白依赖性机制靶向 P/Q 型钙通道，从而使神经元过度钙离子过载。由于 P/Q 亚型钙通道在新生儿神经元（例如 P4-6）中比后期更为突出，我们推测这种 P/Q 型钙电流的特定增强可能导致听觉和其他脑区中新生儿对高胆红素血症的早期神经元易感性。
