Link to bioRxiv paper: http://biorxiv.org/cgi/content/short/2020.10.12.336503v1?rss=1 Authors: Grabner, C. P., Moser, T. Abstract: Rod photoreceptors (PRs) use ribbon synapses to transmit visual information. To signal 'no light detected' they release glutamate continually to activate post-synaptic receptors, and 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) rods. Wild type rods created a readily releasable pool (RRP) of 92 synaptic vesicles (SVs) that emptied as a single kinetic phase with a {tau} < 0.4 msec. Lowering intracellular Ca2+-buffering accelerated Cav channel opening and facilitated release kinetics, but RRP size was unaltered. In contrast, ribbonless rods created an RRP of 24 SVs, and lacked Cav channel facilitation; however, Ca2+ channel-release coupling remained tight. The release deficits caused a sharp attenuation of rod-driven light responses measured from RIBEYE-ko mice. We conclude that the synaptic ribbon facilitates Ca2+-influx and establishes a large RRP of SVs. Copy rights belong to original authors. Visit the link for more info