Kirischuk Sergei, Grantyn Rosemarie
Developmental Physiology, Johannes Müller Institute of Physiology, Humboldt University Medical School (Charité), 10117 Berlin, Germany.
J Neurophysiol. 2002 Oct;88(4):2172-6. doi: 10.1152/jn.2002.88.4.2172.
The elevation of presynaptic calcium concentration is a crucial step in excitation-secretion coupling. However, the amplitudes of action-potential-induced presynaptic calcium transients can display high variability among different terminals. The aim of this study was to clarify whether, at individual boutons, synaptic strength correlates with the average amplitude of presynaptic calcium transients. Low-density collicular cultures were loaded with the calcium indicator Oregon Green bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA) 1. Action potentials were blocked with tetrodotoxin. Presynaptic terminals were identified with FM4-64, a use-dependent vesicle marker. Presynaptic calcium influx was elicited by a focal electrical stimulation of single boutons. Whole cell patch-clamp and calcium imaging techniques were used to record GABAergic evoked inhibitory postsynaptic currents (eIPSCs) and presynaptic fluorescence changes in the stimulated terminal. To make the eIPSCs from different boutons comparable, they were normalized to the mean value of miniature IPSCs (mIPSCs) of the postsynaptic cell. Records from 47 boutons showed that eIPSCs varied between 0.5 and 3.0 and presynaptic calcium transients varied between 0.1 and 1.3. However, there was a strong correlation between the mean amplitudes of eIPSCs and presynaptic calcium responses. The eIPSC-Ca(2+) relationship allows to use the amplitudes of presynaptic calcium transients as an indicator of release efficacy and, in a set of contacts made by one axon, to predict the relative impact of individual terminals.
突触前钙浓度的升高是兴奋-分泌偶联中的关键步骤。然而，动作电位诱发的突触前钙瞬变的幅度在不同终末之间可能表现出很大的变异性。本研究的目的是阐明在单个突触小体处，突触强度是否与突触前钙瞬变的平均幅度相关。用钙指示剂 Oregon Green bis-(o-氨基苯氧基)-N,N,N',N'-四乙酸（BAPTA）1 加载低密度的视丘培养物。用河豚毒素阻断动作电位。用 FM4-64（一种依赖使用的囊泡标记物）鉴定突触前终末。通过对单个突触小体的局部电刺激引发突触前钙内流。使用全细胞膜片钳和钙成像技术记录 GABA 能诱发的抑制性突触后电流（eIPSCs）以及受刺激终末的突触前荧光变化。为了使来自不同突触小体的 eIPSCs 具有可比性，将它们归一化到突触后细胞微小 IPSCs（mIPSCs）的平均值。来自 47 个突触小体的记录显示，eIPSCs 在 0.5 到 3.0 之间变化，突触前钙瞬变在 0.1 到 1.3 之间变化。然而，eIPSCs 的平均幅度与突触前钙反应之间存在很强的相关性。eIPSC-Ca(2+)关系使得可以将突触前钙瞬变的幅度用作释放效率的指标，并在由一个轴突形成的一组突触接触中预测单个终末的相对影响。
