Spatially non-overlapping Ca2+ signals drive distinct forms of neurotransmission
Camille S. Wang, Lisa M. Monteggia, Ege T. Kavalali
Abstract
Calcium (Ca 2+ ) signaling is tightly regulated within a presynaptic bouton. Here, we visualize Ca 2+ signals within hippocampal presynaptic boutons using GCaMP8s tagged to synaptobrevin, a synaptic vesicle protein. We identify evoked presynaptic Ca 2+ transients (ePreCTs) that derive from synchronized voltage-gated Ca 2+ channel openings, spontaneous presynaptic Ca 2+ transients (sPreCTs) that originate from ryanodine sensitive Ca 2+ stores, and a baseline Ca 2+ signal that arises from stochastic voltage-gated Ca 2+ channel openings. We find that baseline Ca 2+ , but not sPreCTs, contributes to spontaneous glutamate release. We employ photobleaching as a use-dependent tool to probe nano-organization of Ca 2+ signals and observe that all three occur in non-overlapping domains within the synapse at near-resting conditions. However, increased depolarization induces intermixing of these Ca 2+ domains via both local and non-local synaptic vesicle turnover. Our findings reveal nanosegregation of Ca 2+ signals within a presynaptic terminal that derive from multiple sources and in turn drive specific modes of neurotransmission.