Coleman William L, Bykhovskaia Maria
Department of Biological Sciences, Lehigh University, 111 Research Dr., Bethlehem, PA 18015, USA.
Mol Cell Neurosci. 2009 Jun;41(2):286-96. doi: 10.1016/j.mcn.2009.03.008. Epub 2009 Apr 5.
Rab3a is a small GTP-binding protein associated with presynaptic vesicles. We have measured the releasable pool in the neuromuscular junction of Rab3a(-) mice by recordings of the asynchronous release activity produced by local applications of hypertonic solutions and demonstrated that the releasable pool is significantly reduced in Rab3a(-) synapses. We found that the activity-dependent vesicle recruitment, as well as the synaptic enhancement associated with it, is disrupted in Rab3a(-) synapses. We employed Ca2+ chelators and disruption of Ca2+ sensitivity of fusion machinery by botulinum neurotoxin type-A microinjections, and demonstrated that local Ca2+ elevation may overcome the Rab3a deficiency in maintaining the releasable pool. Rab3a(-) terminals demonstrated a small but significant low-frequency depression, probably due to insufficient refilling of the releasable pool. Our results, taken together, support the hypothesis that Rab3a maintains the pool of fusion competent vesicles tightly coupled to Ca2+ channels.
Rab3a是一种与突触前囊泡相关的小GTP结合蛋白。我们通过记录局部应用高渗溶液产生的异步释放活性，测量了Rab3a基因敲除小鼠神经肌肉接头处的可释放池，并证明Rab3a基因敲除突触中的可释放池显著减少。我们发现，Rab3a基因敲除突触中依赖活动的囊泡募集及其相关的突触增强受到破坏。我们使用了钙离子螯合剂，并通过A型肉毒杆菌神经毒素微注射破坏融合机制的钙离子敏感性，证明局部钙离子升高可能克服Rab3a缺陷对维持可释放池的影响。Rab3a基因敲除的终末表现出轻微但显著的低频抑制，这可能是由于可释放池的再填充不足所致。我们的研究结果共同支持了这样一种假说，即Rab3a维持与钙离子通道紧密偶联的有融合能力的囊泡池。
