Figure 5.

A model to account for the kinetics of endocytosis and its modulation by calcium. (A) The localized Ca²⁺ signal generated by a brief stimulus normally causes all rapidly releasable vesicles (black) to be retrieved by the fast mode of endocytosis. (B) Excess EGTA suppresses the Ca²⁺ signal at the active zone, so only a fraction of vesicles are switched to the fast mode of endocytosis. Remaining membrane is retrieved by slow endocytosis. Note that EGTA is expected to buffer the Ca²⁺ signal at the active zone of bipolar cells (24).