Exocytosis at the Ribbon Synapse of Retinal Bipolar Cells Studied in Patches of Presynaptic Membrane
Exocytosis at the Ribbon Synapse of Retinal Bipolar Cells Studied in Patches of Presynaptic Membrane
复制标题
在突触前膜斑块中研究视网膜双极细胞带状突触的胞吐作用
作者：
A. Llobet;Anne Cooke;L. Lagnado
通过测量视网膜双极细胞突触前膜贴附斑块的电容和电导变化，研究了双极细胞突触末端胞外位点和离子通道的分布。斑块去极化诱发的电容和电导增加可以通过阻断Ca2+内流或在末端加载EGTA来抑制。当去极化接近Ca2+的逆转电位时，电容的增加下降，表明这是Ca2+依赖性胞吐的结果。电导增加是由钙离子内流激活的KCa通道引起的。两项观察结果表明，胞吐和内吞作用位点与Ca2+通道和kcachannchannels簇共定位；胞吐的初始速率与KCa通道的激活相关，而41%缺乏这种电导的斑块不发生胞吐。电镜观察显示，在每个以带状标记的活性区有~ 16个囊泡停靠在质膜上，但囊泡也以1.5/μm2的密度附着在膜的其余部分。条带的密度为0.10±0.02/μm2，预测约43%的细胞贴片缺乏活性区。因此，通过电容和电导响应测定的Ca2+通道簇的密度与条带的密度相似。这些结果与Ca2+通道簇与带状共定位的观点一致，但不排除钙通道也发生在其他部位的可能性。停靠在质膜上的囊泡的广泛分布表明，胞吐也可能是由Ca2+通道簇的Ca2+扩散引起的。
The distribution of exocytic sites and ion channels in the synaptic terminal of retinal bipolar cells was investigated by measuring capacitance and conductance changes in cell-attached patches of presynaptic membrane. Patch depolarization evoked capacitance and conductance increases that were inhibited by blocking Ca2+ influx or loading the terminal with EGTA. The increase in capacitance declined as the depolarization approached the reversal potential for Ca2+, indicating that it was a result of Ca2+-dependent exocytosis. The conductance increase was caused by KCa channels that were also activated by Ca2+ influx. Two observations indicated that sites of exocytosis and endocytosis colocalized with clusters of Ca2+ channels and KCachannels; the initial rate of exocytosis was correlated with the activation of KCa channels, and exocytosis did not occur in the 41% of patches lacking this conductance. Electron microscopy demonstrated that there were ∼16 vesicles docked to the plasma membrane at each active zone marked by a ribbon, but vesicles were also attached to the rest of the membrane at a density of 1.5/μm2. The density of ribbons was 0.10 ± 0.02/μm2, predicting that ∼43% of cell-attached patches would lack an active zone. The density of Ca2+ channel clusters assayed by capacitance and conductance responses was therefore similar to the density of ribbons. These results are consistent with the idea that Ca2+channel clusters were colocalized with ribbons but do not exclude the possibility that calcium channels also occurred at other sites. The wide distribution of vesicles docked to the plasma membrane suggests that exocytosis might also be triggered by the spread of Ca2+ from Ca2+ channel clusters.
影响因子：
5.5
作者：
Hsu, SF;Jackson, MB
通讯作者：
Jackson, MB