Cellular and Molecular Synaptic Function Unit, Okinawa Institute of Science and Technology - Graduate University, Okinawa, Japan.
Elife. 2024 Jun 3;12:RP90497. doi: 10.7554/eLife.90497.
After exocytosis, release sites are cleared of vesicular residues to replenish with transmitter-filled vesicles. Endocytic and scaffold proteins are thought to underlie this site-clearance mechanism. However, the physiological significance of this mechanism at diverse mammalian central synapses remains unknown. Here, we tested this in a physiologically optimized condition using action potential evoked EPSCs at fast calyx synapse and relatively slow hippocampal CA1 synapse, in post-hearing mice brain slices at 37°C and in 1.3 mM [Ca]. Pharmacological block of endocytosis enhanced synaptic depression at the calyx synapse, whereas it attenuated synaptic facilitation at the hippocampal synapse. Block of scaffold protein activity likewise enhanced synaptic depression at the calyx but had no effect at the hippocampal synapse. At the fast calyx synapse, block of endocytosis or scaffold protein activity significantly enhanced synaptic depression as early as 10 ms after the stimulation onset. Unlike previous reports, neither endocytic blockers nor scaffold protein inhibitors prolonged the recovery from short-term depression. We conclude that the release-site clearance by endocytosis can be a universal phenomenon supporting vesicle replenishment at both fast and slow synapses, whereas the presynaptic scaffold mechanism likely plays a specialized role in vesicle replenishment predominantly at fast synapses.
胞吐作用后，释放位点会清除囊泡残余物，以便填充充满递质的囊泡。内吞作用和支架蛋白被认为是这种位点清除机制的基础。然而，这种机制在不同哺乳动物中枢突触中的生理意义仍然未知。在这里，我们在生理优化的条件下对此进行了测试，使用动作电位诱发的 EPSC 在快速钙簇突触和相对较慢的海马 CA1 突触中，在 37°C 和 1.3mM[Ca]的听力后小鼠脑切片中进行测试。内吞作用的药理学阻断增强了钙簇突触的突触抑制，而减弱了海马突触的突触易化。支架蛋白活性的阻断同样增强了钙簇突触的突触抑制，但对海马突触没有影响。在快速钙簇突触中，内吞作用或支架蛋白活性的阻断在刺激开始后 10ms 即可显著增强突触抑制。与之前的报道不同，内吞作用阻断剂或支架蛋白抑制剂都不会延长从短期抑制中恢复的时间。我们得出结论，内吞作用的释放位点清除可能是支持快速和慢速突触囊泡补充的普遍现象，而突触前支架机制可能在快速突触的囊泡补充中发挥专门作用。
