Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.
Synaptic Nanophysiology Group, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany.
Elife. 2021 Oct 7;10:e63844. doi: 10.7554/eLife.63844.
Rod photoreceptors (PRs) use ribbon synapses to transmit visual information. To signal 'no light detected' they release glutamate continually to activate post-synaptic receptors. When light is detected glutamate release pauses. How a rod's individual ribbon enables this process was studied here by recording evoked changes in whole-cell membrane capacitance from wild-type and ribbonless (-ko) mice. Wild-type rods filled with high (10 mM) or low (0.5 mM) concentrations of the Ca-buffer EGTA created a readily releasable pool (RRP) of 87 synaptic vesicles (SVs) that emptied as a single kinetic phase with a τ<0.4 ms. The lower concentration of EGTA accelerated Ca channel opening and facilitated release kinetics. In contrast, ribbonless rods created a much smaller RRP of 22 SVs, and they lacked Ca channel facilitation; however, Ca channel-release coupling remained tight. These release deficits caused a sharp attenuation of rod-driven scotopic light responses. We conclude that the synaptic ribbon facilitates Ca-influx and establishes a large RRP of SVs.
杆状光感受器（PR）利用带状突触来传递视觉信息。为了发出“未检测到光”的信号，它们持续释放谷氨酸以激活突触后受体。当检测到光时，谷氨酸的释放会暂停。在这里，通过记录来自野生型和无带状（-ko）小鼠的全细胞膜电容的诱发变化，研究了单个带状物如何使这一过程成为可能。用高浓度（10 mM）或低浓度（0.5 mM）钙缓冲剂 EGTA 填充的野生型杆状细胞会产生一个 87 个突触小泡（SV）的易释放池（RRP），这些 SV 以单一动力学相排空，τ<0.4 ms。较低浓度的 EGTA 加速了钙通道的开放并促进了释放动力学。相比之下，无带状的杆状细胞产生的 RRP 要小得多，只有 22 个 SV，并且它们缺乏钙通道的促进作用；然而，钙通道释放的耦联仍然很紧密。这些释放缺陷导致杆状驱动的暗视光反应明显衰减。我们得出结论，突触带促进了 Ca 流入并建立了大量的 SV 易释放池。
