Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, USA; Pharmacology and Experimental Neuroscience, USA.
Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, USA.
Exp Eye Res. 2022 Dec;225:109279. doi: 10.1016/j.exer.2022.109279. Epub 2022 Oct 22.
Synaptotagmins are the primary Ca sensors for synaptic exocytosis. Previous work suggested synaptotagmin-1 (Syt1) mediates evoked vesicle release from cone photoreceptor cells in the vertebrate retina whereas release from rods may involve another sensor in addition to Syt1. We found immunohistochemical evidence for syntaptotagmin-7 (Syt7) in mouse rod terminals and so performed electroretinograms (ERG) and single-cell recordings using mice in which Syt1 and/or Syt7 were conditionally removed from rods and/or cones. Synaptic release was measured in mouse rods by recording presynaptic anion currents activated during glutamate re-uptake and from exocytotic membrane capacitance changes. Deleting Syt1 from rods reduced glutamate release evoked by short depolarizing steps but not long steps whereas deleting Syt7 from rods reduced release evoked by long but not short steps. Deleting both sensors completely abolished depolarization-evoked release from rods. Effects of various intracellular Ca buffers showed that Syt1-mediated release from rods involves vesicles close to ribbon-associated Ca channels whereas Syt7-mediated release evoked by longer steps involves more distant release sites. Spontaneous release from rods was unaffected by eliminating Syt7. While whole animal knockout of Syt7 slightly reduced ERG b-waves and oscillatory potentials, selective elimination of Syt7 from rods had no effect on ERGs. Furthermore, eliminating Syt1 from rods and cones abolished ERG b-waves and additional elimination of Syt7 had no further effect. These results show that while Syt7 contributes to slow non-ribbon release from rods, Syt1 is the principal sensor shaping rod and cone inputs to bipolar cells in response to light flashes.
突触结合蛋白是突触胞吐的主要 Ca 传感器。先前的工作表明，突触结合蛋白-1（Syt1）介导脊椎动物视网膜中的锥体光感受器细胞的诱发囊泡释放，而除了 Syt1 之外，从杆状细胞释放可能还涉及另一个传感器。我们在小鼠杆状终末中发现了突触结合蛋白-7（Syt7）的免疫组织化学证据，因此使用条件性从杆状细胞和/或锥体中去除 Syt1 和/或 Syt7 的小鼠进行了视网膜电图（ERG）和单细胞记录。通过记录谷氨酸再摄取过程中激活的突触前阴离子电流以及从胞吐膜电容变化中，在小鼠杆状细胞中测量突触释放。从杆状细胞中删除 Syt1 会减少由短去极化步骤引起的谷氨酸释放，但不会减少由长去极化步骤引起的释放，而从杆状细胞中删除 Syt7 则减少由长去极化步骤引起的释放，但不会减少由短去极化步骤引起的释放。完全删除两个传感器会完全消除从杆状细胞中引起的去极化诱发释放。各种细胞内 Ca 缓冲液的作用表明，Syt1 介导的从杆状细胞释放涉及靠近带相关 Ca 通道的囊泡，而由较长步骤引发的 Syt7 介导的释放涉及更远的释放位点。消除 Syt7 对杆状细胞的自发释放没有影响。虽然 Syt7 的整体动物敲除略微降低了 ERG b 波和振荡电位，但从杆状细胞中选择性消除 Syt7 对 ERG 没有影响。此外，从杆状细胞和锥体中消除 Syt1 会消除 ERG b 波，而进一步消除 Syt7 则没有进一步的影响。这些结果表明，虽然 Syt7 有助于从杆状细胞中缓慢的非带状释放，但 Syt1 是塑造杆状细胞和锥体输入到双极细胞以响应光闪光的主要传感器。
