Separation of presynaptic Ca2 and Ca1 channel function in synaptic vesicle exo- and endocytosis by the membrane anchored Ca pump PMCA.

Synaptic vesicle (SV) release, recycling, and plastic changes of release probability co-occur side by side within nerve terminals and rely on local Ca signals with different temporal and spatial profiles. The mechanisms that guarantee separate regulation of these vital presynaptic functions during action potential (AP)-triggered presynaptic Ca entry remain unclear. Combining genetics with electrophysiology and imaging reveals the localization of two different voltage-gated calcium channels at the presynaptic terminals of glutamatergic neuromuscular synapses (the Ca2 homolog, Dmca1A or cacophony, and the Ca1 homolog, Dmca1D) but with spatial and functional separation. Ca2 within active zones is required for AP-triggered neurotransmitter release. By contrast, Ca1 localizes predominantly around active zones and contributes substantially to AP-evoked Ca influx but has a small impact on release. Instead, L-type calcium currents through Ca1 fine-tune short-term plasticity and facilitate SV recycling. Separate control of SV exo- and endocytosis by AP-triggered presynaptic Ca influx through different channels demands efficient measures to protect the neurotransmitter release machinery against Ca1-mediated Ca influx. We show that the plasma membrane Ca ATPase (PMCA) resides in between active zones and isolates Ca2-triggered release from Ca1-mediated dynamic regulation of recycling and short-term plasticity, two processes which Ca2 may also contribute to. As L-type Ca1 channels also localize next to PQ-type Ca2 channels within axon terminals of some central mammalian synapses, we propose that Ca2, Ca1, and PMCA act as a conserved functional triad that enables separate control of SV release and recycling rates in presynaptic terminals.