Figure 5.

Synaptic vesicle endocytosis. A, The principle of membrane capacitance measurements. Exocytic fusion of vesicles increases the surface area of nerve terminal plasma membranes, thereby causing an abrupt increase in presynaptic membrane capacitance (ΔC_m) as monitored with a whole-cell patch pipette connected to a lock-in amplifier. During endocytosis, membrane retrieval of multiple vesicles gradually decreases whole-terminal membrane capacitance. B, GTPγS (200 µM) loaded into the calyx terminal blocks endocytosis with no immediate effect on exocytosis (upper traces, with or without GTPγS, superimposed).⁶²⁾ However, exocytosis gradually declines to a low level during repetitive stimulation in a use-dependent manner (lower panel). C, Intra-terminal loading of EGTA (10 mM, red trace) or BAPTA (1 mM, blue) attenuates both exocytosis and endocytosis at the calyx of Held before hearing onset. In the bottom panel, records are normalized at the exocytic ΔC_m amplitude and superimposed to show the time course of endocytosis slowed by Ca²⁺ chelators.⁶⁶⁾