Department of Physiology and Biomembrane Plasticity Research Center, Seoul National University College of Medicine and Neuroscience Research Institute, Seoul 110-799, Korea.
J Gen Physiol. 2010 Sep;136(3):259-72. doi: 10.1085/jgp.201010437.
Post-tetanic potentiation (PTP) at the calyx of Held synapse is caused by increases not only in release probability (P(r)) but also in the readily releasable pool size estimated from a cumulative plot of excitatory post-synaptic current amplitudes (RRP(cum)), which contribute to the augmentation phase and the late phase of PTP, respectively. The vesicle pool dynamics underlying the latter has not been investigated, because PTP is abolished by presynaptic whole-cell patch clamp. We found that supplement of recombinant calmodulin to the presynaptic pipette solution rescued the increase in the RRP(cum) after high-frequency stimulation (100 Hz for 4-s duration, HFS), but not the increase in P(r). Release-competent synaptic vesicles (SVs) are heterogeneous in their releasing kinetics. To investigate post-tetanic changes of fast and slowly releasing SV pool (FRP and SRP) sizes, we estimated quantal release rates before and 40 s after HFS using the deconvolution method. After HFS, the FRP size increased by 19.1% and the SRP size decreased by 25.4%, whereas the sum of FRP and SRP sizes did not increase. Similar changes in the RRP were induced by a single long depolarizing pulse (100 ms). The post-tetanic complementary changes of FRP and SRP sizes were abolished by inhibitors of myosin II or myosin light chain kinase. The post-tetanic increase in the FRP size coupled to a decrease in the SRP size provides the first line of evidence for the idea that a slowly releasing SV can be converted to a fast releasing one.
突触后强直增强（PTP）在 Held 神经节突触的终扣处是由释放概率（P(r)）的增加和易释放池大小（RRP(cum)）的增加引起的，RRP(cum)可以通过兴奋性突触后电流幅度的累积图来估计，这分别有助于增强相和 PTP 的晚期相。尚未研究后者的囊泡池动力学，因为 PTP 会被突触前全细胞膜片钳消除。我们发现，将重组钙调蛋白添加到突触前管内液中可以挽救高频刺激（100 Hz 持续 4 秒，HFS）后 RRP(cum)的增加，但不能挽救 P(r)的增加。释放能力的突触小泡（SV）在释放动力学方面具有异质性。为了研究强直后快速和慢速释放 SV 池（FRP 和 SRP）大小的变化，我们使用反卷积方法在 HFS 之前和之后 40 秒估计了量子释放率。HFS 后，FRP 大小增加了 19.1%，SRP 大小减少了 25.4%，而 FRP 和 SRP 大小的总和没有增加。单个长去极化脉冲（100 ms）也会引起类似的 RRP 变化。肌球蛋白 II 或肌球蛋白轻链激酶抑制剂可消除 FRP 和 SRP 大小的强直后互补变化。FRP 大小的强直后增加与 SRP 大小的减少相结合，为缓慢释放 SV 可以转化为快速释放 SV 的观点提供了第一个证据。
