Dunn T W, McCamphill P K, Syed N I
Faculty of Medicine, Hotchkiss Brain Institute, University of Calgary, Calgary, Alberta T2N 4N1, Canada.
Synapse. 2009 Feb;63(2):117-25. doi: 10.1002/syn.20589.
Spontaneous transmitter release has been observed at various synapses that permit analysis at a sufficient resolution as a miniature postsynaptic potential (mPSP). However, the precise mechanisms that regulate spontaneous transmitter release have not yet been fully defined. Activity and ligand-mediated modulation of large amplitude, spontaneous events significantly enhances postsynaptic excitation in the absence of action potential activity suggesting a more complicated role for this mode of transmitter release, and thus warrants further analysis. Here, we used Lymnaea soma-soma synaptic connections to demonstrate that a transient increase in both the frequency and amplitude of spontaneous events (mPSPs) occurs following a short burst of action potentials in the presynaptic cell. These events were of presynaptic origin and the increase in mPSP amplitude could also be achieved with a stimulatory concentration of ryanodine. Ryanodine also occluded the activity-induced increase in mPSP amplitude implicating calcium release from these channels in the production of large amplitude spontaneous transmitter release events. This suggests that presynaptic activity triggers ryanodine receptor-mediated large amplitude minis, indicating that although these events are action potential-independent, they are nevertheless responsive to the prior activity of the synapse.
在各种突触中都观察到了自发递质释放现象，这些突触能够以足够的分辨率进行分析，表现为微小的突触后电位（mPSP）。然而，调节自发递质释放的精确机制尚未完全明确。在没有动作电位活动的情况下，对大幅度自发事件的活动和配体介导的调节显著增强了突触后兴奋，这表明这种递质释放模式具有更复杂的作用，因此值得进一步分析。在这里，我们利用椎实螺体-体突触连接来证明，在突触前细胞中短串动作电位之后，自发事件（mPSP）的频率和幅度都会出现短暂增加。这些事件起源于突触前，mPSP幅度的增加也可以通过刺激浓度的ryanodine来实现。Ryanodine还阻断了活动诱导的mPSP幅度增加，这意味着这些通道释放的钙参与了大幅度自发递质释放事件的产生。这表明突触前活动触发了ryanodine受体介导的大幅度微小电位，这表明尽管这些事件不依赖于动作电位，但它们仍然对突触的先前活动有反应。
