Figure 4.

Rises in global [Ca²⁺] altered the kinetics of endocytosis. (A) Capacitance responses in terminals loaded with 0.5, 2, and 40–75 mM EGTA. Compared are responses to stimuli of 20 ms (black traces) and 500 ms (red). Traces are averaged responses (n = 6, 7, and 12, respectively) and are unscaled. (B) The responses to the 500-ms stimuli from A scaled to the same maximum to allow comparison of their kinetics. The parameters of the fitted traces (bold) are shown in Table 2. The time course of endocytosis is also compared with the fall in [Ca²⁺], estimated from the Ca²⁺-activated tail current using a conversion factor of 9 pA/μM (blue trace). The averaged Ca²⁺ currents that elicited these capacitance responses are shown below (black). In 0.5 mM EGTA, the fall in capacitance was not obvious until the free [Ca²⁺] fell below about ∼1.5 μM (arrow). (C) The proportion of membrane retrieved by fast endocytosis as a function of the [EGTA] in the patch pipette. This analysis is confined to responses elicited by brief stimuli (including those shown by the black traces in A).