TY - JOUR TI - The mammalian rod synaptic ribbon is essential for Cav channel facilitation and ultrafast synaptic vesicle fusion AU - Grabner, Chad Paul AU - Moser, Tobias A2 - Rieke, Fred A2 - Aldrich, Richard W A2 - Rieke, Fred A2 - Singer, Joshua H A2 - Thoreson, Wallace B VL - 10 PY - 2021 DA - 2021/10/07 SP - e63844 C1 - eLife 2021;10:e63844 DO - 10.7554/eLife.63844 UR - https://doi.org/10.7554/eLife.63844 AB - 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 (Ribeye-ko) mice. Wild-type rods filled with high (10 mM) or low (0.5 mM) concentrations of the Ca2+-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 Cav channel opening and facilitated release kinetics. In contrast, ribbonless rods created a much smaller RRP of 22 SVs, and they lacked Cav channel facilitation; however, Ca2+ 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 Ca2+-influx and establishes a large RRP of SVs. KW - synaptic ribbon KW - rod photoreceptor KW - exocytosis KW - synaptic transmission KW - calcium channels KW - active zone JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -