| The inner hair cell (IHC) is the primary sensory cell of the cochlea exciting the auditory nerve in response to incoming sound. Deflections of the IHC's stereocilla caused by movements of the tectorial membrane and hair cells relative to each other, gate stereociliar mechanosensitive transducer channels. The transduction current depolarizes the cell, thereby opening basolateral voltage-gated Ca2+ and K+ channels. The resulting Ca2+ influx at the ribbon-type active zones triggers exocytosis of synaptic vesicles, which probably release glutamate onto glutamate receptors of the postsynaptic auditory nerve fibers.In the mammalian cochlea, some 10-30 afferent fibers each form a single bouton-like ending on one inner hair cell, and most such contacts are served by a single synaptic ribbon. The single active zone provides the entire acoustic signal for an afferent fiber, including ongoing spontaneous activity up to 1 00Hz, evoked action potentials at maximan rates of 3 00Hz. In fact mammalian inner hair cell can transmit timing information about sound signals with frequencies of up to 2kHz, and IHCs can maintain transmitter release in response to sustained sound stimuli that last for hours.The extraordinary performance of the inner ear afferent synapses sets highdemonds on the voltage-gated Ca2+ channle that control the neurotransmitter release from presynaptic.Different types of voltage-gated Ca2+ channels mediated depolarization induced Ca2+ influx across the plasma membrane of electrically excitable cells. One class, 1D L-type Ca2+ channels (D-LTCC), which activated by strong depolarizations and are modulated by low concentrations of different chemical classes of Ca2+ antagonists including Nifidipine, are thought to be the voltage-gated Ca2+ channels which mediated the neurotransmitter release in inner hair cell.D-LTCC is also expressed in other tissue. In neuroendocrine cells, including pancreatic cells, Ca2+ influx through D-LTCC triggers hormone secretion. In neurons, D-LTCCs are preferentially located at cell bodies and dendrites and play only minor role for neurotransmitter release at nerve terminals. Ca2+ influx through neuronal LTCCs into the cell soma modulates gene transcription, thus coupling synaptic excitation to transcriptional events thought to contribute to neuronal plasticity. It's evendent that D-LTCCs take different roles in specific tissue. In addition, the splice varient cloning from the cells or neurons and then expressed in vitro can not mimick the properties of the Ca + channel which mediated Ca2+ influx in inner hair cells at least in low activation threshold and inactivation characteristic.But how can one gene generate such divergent proteins in different tissue and what are the molecular bases for these phynotype?Alternative pre-mRNA splicing is considered to be the most important source of protein diversity in vertebrates. In this study, we exploited the RT-PCRto investigate whether alternative pre-mRNA splicing take a role in the generation of divergent D-LTCCs that specifically expressed in cochlea. Our results demonstrate that the am mRNA in rat cochlea is spliced in a tissue-specific manner: 63bp was exluded from mature mRNA in exon3, the exon12 was deleted in I-II loop and there are three splicing patterns in carboxyl terminus, one (type A) is similar to the isoform cloning from pancreatic cell, but the isoform expressed in P cell lack the exon46, the second splicing variant (type B) exist predominantly in cochlea and include a 153bp-deletion in the beginning of exon48, the third type of splicing pattern (type C) happened in cochlea and exon44-46 were excluded which produce a mRNA with a short carboxyl ternimus.The I-II loop and C-terminal are the most important part of the Ca2+ channels, the P subunit can bind to these sites and modulate the dynamics of 1 subunit. We propose that the alternative splicing of the OID mRNA contributes tothe unusual dynamics of the hair cell's voltage-gated Ca channels by interact with P subunit.We als...
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