Figure 2.

Four hypothetical mechanisms by which synapses sense exocytosis and initiate endocytosis in time and space. (A) Ca²⁺ is a trigger, and synaptotagmin and CaM are sensors in the SV exocytosis-endocytosis coupling. (B) SV fusion is a trigger, and SV proteins (both transmembrane and associated proteins) are sensors to initiate CME by interacting with AP-2. (C) SV fusion is a trigger to generate the local membrane stress. (D) The annular spatial arrangement of EZs surrounding AZs. The large scaffolds are critical for SV exocytosis-endocytosis coupling by facilitating SV proteins transportation and recapture.