Rusakov D A
Institute of Neurology, University College London, London WC1N 3BG, United Kingdom.
Biophys J. 2001 Oct;81(4):1947-59. doi: 10.1016/S0006-3495(01)75846-8.
Recent findings suggest that rapid activation of extrasynaptic receptors and transient depletion of extracellular Ca(2+) may represent an important component of glutamatergic synaptic transmission. These phenomena imply a previously unrecognized role for synaptic glial sheaths: to retard extracellular diffusion in the synaptic vicinity. The present study is an attempt to assess the extent and physiological implications of this retardation using a detailed compartmental model of the typical synaptic environment. The model allows reconstruction of a partial (asymmetric) glial sheath covered with transporter molecules, which gives a more realistic representation of the vicinity of central synapses. Simulations show to what extent, in conditions compatible with physiology, the occupancy of synaptic receptors and the depletion of Ca(2+) in the cleft increase with increased glial coverage. The impact of glial sheaths on synaptic transmission is shown to become greater with smaller synapses and with slower kinetics of perisynaptic ion transients. At a calyceal synapse, a profound temporal filtering of fast Ca(2+) influx is found, and similar phenomena are predicted to occur following simultaneous activation of multiple synapses in the neuropil. The results provide a quantitative guidance for interpretation of physiological experiments that address fast transients of neurotransmitters and small ions in the brain tissue.
最近的研究结果表明，突触外受体的快速激活和细胞外Ca(2+)的短暂消耗可能是谷氨酸能突触传递的一个重要组成部分。这些现象暗示了突触胶质鞘以前未被认识到的作用：减缓突触附近的细胞外扩散。本研究试图使用典型突触环境的详细房室模型来评估这种减缓的程度和生理意义。该模型允许重建覆盖有转运分子的部分（不对称）胶质鞘，这更真实地反映了中枢突触附近的情况。模拟显示，在符合生理学的条件下，随着胶质覆盖增加，突触受体的占有率和突触间隙中Ca(2+)的消耗增加到何种程度。结果表明，对于较小的突触和突触周围离子瞬变动力学较慢的情况，胶质鞘对突触传递的影响会更大。在杯状突触处，发现对快速Ca(2+)内流有深刻的时间过滤作用，并且预计在神经毡中多个突触同时激活后会出现类似现象。这些结果为解释解决脑组织中神经递质和小离子快速瞬变的生理实验提供了定量指导。
