Shen Yiru, Yu Dejie, Hiel Hakim, Liao Ping, Yue David T, Fuchs Paul A, Soong Tuck Wah
Department of Physiology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597.
J Neurosci. 2006 Oct 18;26(42):10690-9. doi: 10.1523/JNEUROSCI.2093-06.2006.
Native Ca(V)1.3 channels within cochlear hair cells exhibit a surprising lack of Ca2+-dependent inactivation (CDI), given that heterologously expressed Ca(V)1.3 channels show marked CDI. To determine whether alternative splicing at the C terminus of the Ca(V)1.3 gene may produce a hair cell splice variant with weak CDI, we transcript-scanned mRNA obtained from rat cochlea. We found that the alternate use of exon 41 acceptor sites generated a splice variant that lost the calmodulin-binding IQ motif of the C terminus. These Ca(V)1.3(IQdelta) ("IQ deleted") channels exhibited a lack of CDI, which was independent of the type of coexpressed beta-subunits. Ca(V)1.3(IQdelta) channel immunoreactivity was preferentially localized to cochlear outer hair cells (OHCs), whereas that of Ca(V)1.3(IQfull) channels (IQ-possessing) labeled inner hair cells (IHCs). The preferential expression of Ca(V)1.3(IQdelta) within OHCs suggests that these channels may play a role in processes such as electromotility or activity-dependent gene transcription rather than neurotransmitter release, which is performed predominantly by IHCs in the cochlea.
鉴于异源表达的Ca(V)1.3通道表现出明显的钙依赖性失活(CDI)，耳蜗毛细胞内的天然Ca(V)1.3通道却出人意料地缺乏CDI。为了确定Ca(V)1.3基因C末端的可变剪接是否会产生具有弱CDI的毛细胞剪接变体，我们对从大鼠耳蜗获得的mRNA进行了转录扫描。我们发现外显子41受体位点的交替使用产生了一种剪接变体，该变体失去了C末端的钙调蛋白结合IQ基序。这些Ca(V)1.3(IQdelta)（“IQ缺失”）通道表现出缺乏CDI，这与共表达的β亚基类型无关。Ca(V)1.3(IQdelta)通道免疫反应性优先定位于耳蜗外毛细胞(OHC)，而Ca(V)1.3(IQfull)通道（具有IQ）的免疫反应性标记内毛细胞(IHC)。Ca(V)1.3(IQdelta)在OHC中的优先表达表明，这些通道可能在诸如电运动或活动依赖性基因转录等过程中发挥作用，而不是在耳蜗中主要由IHC执行的神经递质释放过程中发挥作用。
