Meshul C K, Pappas G D
Brain Res. 1984 Jan 2;290(1):1-18. doi: 10.1016/0006-8993(84)90730-3.
The fate of the extracellular marker horseradish peroxidase (HRP), following intense transmitter release was studied using identified muscle fibers from the frog sartorius nerve-muscle preparation. The muscle was stimulated indirectly via its nerve at 10 Hz or K+-depolarized for 15 min. Other preparations were also stimulated or K+-depolarized for 15 min and then rested for an additional 15 min. Endings from only identified muscle fibers were photographed with the electron microscope. It was found that in the paradigms studied above, less than 10% of the mean number of synaptic vesicle profiles per section contained the marker. Following electrical stimulation, there was a statistically significant decrease in the mean number of synaptic vesicle profiles per section. After a 15 min rest period, the vesicle profile number had returned to the control value. At this time point, the endplate potential was but 25% of the control. K+-depolarization caused no significant change in the mean number of synaptic vesicle profiles per section. Experiments were also performed to rule out any direct effect of the label on the number of coated and synaptic vesicle profiles. The mean number of labeled coated vesicle profiles increased during either electrical stimulation or K+-depolarization, and then fell during the subsequent rest period. Their numbers accounted for less than 2% of the total number vesicles/section. A suprisingly high number of coated vesicle profiles (as high as 41%) contained no label. This finding is inconsistent with the exclusive role of coated vesicles associated with synaptic vesicle membrane recycling. The low level of HRP labeling of synaptic vesicles is also inconsistent with synaptic vesicles undergoing exo- and endocytosis along the presynaptic plasma membrane.
利用青蛙缝匠肌神经 - 肌肉标本中已鉴定的肌纤维，研究了在大量递质释放后细胞外标记物辣根过氧化物酶（HRP）的命运。通过其神经以10Hz间接刺激肌肉，或用K⁺使其去极化15分钟。其他标本也进行刺激或K⁺去极化15分钟，然后再休息15分钟。仅对已鉴定肌纤维的终末进行电子显微镜拍照。发现在上述研究的模式中，每切片突触小泡轮廓的平均数量中，含有该标记物的不到10%。电刺激后，每切片突触小泡轮廓的平均数量有统计学意义的减少。休息15分钟后，小泡轮廓数量恢复到对照值。此时，终板电位仅为对照值的25%。K⁺去极化并未使每切片突触小泡轮廓的平均数量发生显著变化。还进行了实验以排除标记物对包被小泡和突触小泡轮廓数量的任何直接影响。在电刺激或K⁺去极化期间，标记的包被小泡轮廓的平均数量增加，然后在随后的休息期下降。它们的数量占每切片小泡总数的不到2%。令人惊讶的是，大量的包被小泡轮廓（高达41%）没有标记。这一发现与包被小泡与突触小泡膜再循环相关的唯一作用不一致。突触小泡的HRP标记水平低也与突触小泡沿突触前质膜进行胞吐和胞吞作用不一致。
