Identification of Neurotransmitter released from hair cells

为了确定听觉毛细胞释放的神经递质，我们发明了一种在分离的毛细胞和培养的小脑颗粒细胞之间形成的人工突触。对毛细胞和颗粒细胞进行全细胞电压钳制，分析毛细胞膜去极化对颗粒细胞电流的影响。在膜电位为正的电压钳制下，颗粒细胞可检测到外向电流。该电流可被施加DL-APV的浴液可逆性阻断，因此认为这是由于颗粒细胞上的NMDA型谷氨酸受体激活所致。通过对几种兴奋性氨基酸分别在颗粒细胞和浦肯野细胞上表达的NMDA和非NMDA受体的剂量依赖关系的详细研究，得出结论：谷氨酸是毛细胞最有可能释放的神经递质。当谷氨酸从毛细胞中释放出来时，它可以在0.5秒内动员多达860个突触小泡，这些小泡很可能在毛细胞中的每个活动区以500赫兹的速度与突触前膜融合。

In order to determine the neurotransmitter released from auditory hair cells, we have invented an artificial synapse formed between isolated hair cells and cultured cerebellar granule cells. Both hair cells and granule cells were whole cell voltage clamped, and the current detected in the granule cells in response to the hair cell membrane depolarization were analyzed. Outward current was detected in the granule cells voltaged clamped at positive membrane potentials. This current was blocked reversibly by the bath applied DL-APV,therefore, concluded as due to the activation of NMDA type glutamate receptors on the granule cell. From detailed investigations of the dose-dependencies of several excitatory amino acids for NMDA and non-NMDA receptors expressed on the granule cells and on the Purkinje cells, respectively, glutamate was concluded as the most likely neurotransmitter released from hair cells. When glutamate was released from hair cells, it could mobilized up to 860 synaptic vesicles in 0.5 sec and such vesicles are likely fused with the presynaptic membrane at a rate of 500 Hz at each active zones in the hair cell.