Legendre P
Institut des Neurosciences, Université Pierre et Marie Curie, 75252 Paris Cedex 05, France.
J Neurosci. 1998 Apr 15;18(8):2856-70. doi: 10.1523/JNEUROSCI.18-08-02856.1998.
Miniature IPSCs (mIPSCs) recorded in the Mauthner (M)-cell of zebrafish larvae have a broad amplitude distribution that is attributable only partly to the functional heterogeneity of postsynaptic glycine receptors (GlyRs). The role of the kinetic properties of GlyRs in amplitude fluctuation was investigated using fast-flow application techniques on outside-out patches. Short applications of a saturating glycine concentration evoked outside-out currents with a biphasic deactivation phase as observed for mIPSCs, and they were consistent with a rapid clearance of glycine from the synaptic cleft. Patch currents declined slowly during continuous applications of 3 mM glycine, but the biphasic deactivation phase of mIPSCs cannot reflect a desensitization process because paired-pulse desensitization was not observed. The maximum open probability (Po) of GlyRs was close to 0.9 with 3 mM glycine. Analyses of the onset of outside-out currents evoked by 0.1 mM glycine are consistent with the presence of two equivalent binding sites with a Kd of O.3-O.4 mM. Activation and deactivation properties of GlyRs were better described with a kinetic model, including two binding states, a doubly liganded open state, and a reluctant gating mode leading to another open state. The 20-80% rise time of mIPSCs was independent of their amplitude and is identical to that of outside-out currents evoked by the applications of a saturating concentration of glycine (>1 mM). These results support the hypothesis that GlyR kinetics determines the time course of synaptic events at M-cell inhibitory synapses and that large mIPSC amplitude fluctuations are mainly of postsynaptic origin.
在斑马鱼幼体的Mauthner（M）细胞中记录到的微小抑制性突触后电流（mIPSCs）具有广泛的幅度分布，这仅部分归因于突触后甘氨酸受体（GlyRs）的功能异质性。利用外向膜片钳的快速灌流技术研究了GlyRs的动力学特性在幅度波动中的作用。短暂施加饱和甘氨酸浓度可诱发外向膜片钳电流，其具有如mIPSCs中观察到的双相失活阶段，且这与甘氨酸从突触间隙的快速清除相一致。在持续施加3 mM甘氨酸期间，膜片钳电流缓慢下降，但mIPSCs的双相失活阶段不能反映脱敏过程，因为未观察到成对脉冲脱敏现象。在3 mM甘氨酸条件下，GlyRs的最大开放概率（Po）接近0.9。对0.1 mM甘氨酸诱发的外向膜片钳电流起始阶段的分析与存在两个等效结合位点一致，其解离常数（Kd）为0.3 - 0.4 mM。GlyRs的激活和失活特性用一个动力学模型能更好地描述，该模型包括两个结合状态、一个双配体开放状态以及一种导致另一个开放状态的迟缓门控模式。mIPSCs的20 - 80%上升时间与其幅度无关，且与施加饱和浓度甘氨酸（>1 mM）诱发的外向膜片钳电流的上升时间相同。这些结果支持了以下假设：GlyR动力学决定了M细胞抑制性突触处突触事件的时间进程，且mIPSC幅度的大幅波动主要源于突触后。
