Niu Y P, Xiao M Y, Wigström H
Department of Medical Biophysics, Göteborg University, Medicinaregatan 11, Box 433, SE 405 30, Göteborg, Sweden.
Brain Res. 1998 Aug 3;800(2):253-9. doi: 10.1016/s0006-8993(98)00526-5.
The relative variability of excitatory postsynaptic currents (EPSCs) was studied using whole cell recording in CA1 pyramidal cells of hippocampal slices from 2 to 3-week-old rats. EPSCs were evoked by stimulating the Schaffer collateral-commissural pathway and recorded at holding potentials of -75, -30 or +40 mV. The recordings were either isolated alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) or N-methyl-D-aspartate (NMDA) receptor mediated EPSCs, or composite ones. EPSC variability was quantified by coefficient of variation (CV). The inverse variability expressed as 1/CV2 was employed in comparisons. Using early (5-15 ms) and late (40-100 ms) measurements to estimate the AMPA and NMDA components of composite EPSCs showed no difference in the variability of the two components. Comparing isolated AMPA EPSCs at -75 mV with NMDA EPSCs at -30 mV also failed to reveal a difference. However, in accord with previous studies by others, NMDA EPSCs recorded at +40 mV were less variable than AMPA EPSCs at -75 mV, the ratio of 1/CV2 for NMDA vs. AMPA being around 1.7. A comparison between isolated AMPA EPSCs revealed a similar pattern of dependency of CV on membrane potential, the EPSCs at +40 mV being less variable than those at -30 or -75 mV (1/CV2 ratios of 1.5-1.6). In conclusion, our results did not demonstrate any inherent difference in CV between AMPA and NMDA receptor mediated EPSCs and the observed differences in CV could be accounted for by a dependency on membrane potential, the mechanism of which remains to be resolved. The present results have implications for the interpretation of CV changes as observed, for instance, during synaptic plasticity.
利用全细胞记录技术，在2至3周龄大鼠海马脑片的CA1锥体细胞中研究兴奋性突触后电流（EPSCs）的相对变异性。通过刺激海马联合-连合通路诱发EPSCs，并在-75、-30或+40 mV的钳制电位下进行记录。记录的电流要么是分离的α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA）或N-甲基-D-天冬氨酸（NMDA）受体介导的EPSCs，要么是复合EPSCs。EPSC变异性通过变异系数（CV）进行量化。在比较中采用以1/CV2表示的反向变异性。利用早期（5 - 15毫秒）和晚期（40 - 100毫秒）测量来估计复合EPSCs的AMPA和NMDA成分，结果显示这两种成分的变异性没有差异。将-75 mV下的分离AMPA EPSCs与-30 mV下的NMDA EPSCs进行比较，也未发现差异。然而，与其他人先前的研究一致，在+40 mV记录的NMDA EPSCs比在-75 mV记录的AMPA EPSCs变异性更小，NMDA与AMPA的1/CV2比值约为1.7。对分离的AMPA EPSCs进行比较，发现CV对膜电位的依赖性呈现相似模式，+40 mV下的EPSCs比-30或-75 mV下的EPSCs变异性更小（1/CV2比值为1.5 - 1.6）。总之，我们的结果并未证明AMPA和NMDA受体介导的EPSCs在CV方面存在任何内在差异，观察到的CV差异可能是由对膜电位的依赖性导致的，其机制仍有待解决。目前的结果对解释例如在突触可塑性过程中观察到的CV变化具有启示意义。
