尽管经过几十年的紧张研究,异步神经递质释放的分子基础仍然是神秘的。Synaptotagmin(syt)7和Doc2都被提出作为触发这种胞吐模式的Ca2传感器,但是相互矛盾的发现引发了争议。这里,我们证明,在兴奋性小鼠海马突触,Doc2α是异步释放的主要Ca2+传感器,而syt7通过突触小泡的活性依赖性对接来支持这一过程。在缺乏Doc2α的突触中,单个动作电位强烈降低后的异步释放,而删除syt7没有效果。然而,在没有syt7的情况下,对接的囊泡不能在毫秒时间尺度上得到补充。因此,在重复活动期间,同步和异步释放从第二个脉冲向前按压。相比之下,缺乏Doc2α的突触具有正常的活动依赖性对接,但在多次刺激后继续表现出减少的异步释放。此外,两个Ca2+传感器的破坏都是非加成的。这些发现导致了一个新的模型,即syt7驱动依赖于活动的对接,从而在持续传输期间为同步(syt1)和异步(Doc2和其他未识别的传感器)释放提供突触小泡。
Despite decades of intense study, the molecular basis of asynchronous neurotransmitter release remains enigmatic. Synaptotagmin (syt) 7 and Doc2 have both been proposed as Ca2+ sensors that trigger this mode of exocytosis, but conflicting findings have led to controversy. Here, we demonstrate that at excitatory mouse hippocampal synapses, Doc2α is the major Ca2+ sensor for asynchronous release, while syt7 supports this process through activity-dependent docking of synaptic vesicles. In synapses lacking Doc2α, asynchronous release after single action potentials is strongly reduced, while deleting syt7 has no effect. However, in the absence of syt7, docked vesicles cannot be replenished on millisecond timescales. Consequently, both synchronous and asynchronous release depress from the second pulse onward during repetitive activity. By contrast, synapses lacking Doc2α have normal activity-dependent docking, but continue to exhibit decreased asynchronous release after multiple stimuli. Moreover, disruption of both Ca2+ sensors is non-additive. These findings result in a new model whereby syt7 drives activity-dependent docking, thus providing synaptic vesicles for synchronous (syt1) and asynchronous (Doc2 and other unidentified sensors) release during ongoing transmission.