Fig. 4.

Fast chelation of VDCC-mediated Ca²⁺ influx increases endocytosis. A,C, Ca²⁺-dependent glutamate release from nerve terminals evoked by 30 mm KCl after previous loading with increasing concentrations of either BAPTA-AM or EGTA-AM;n = 4–5 (±SEM). B,D, Nerve terminals were loaded for 2 min with FM2–10 during S1 stimulation with KCl (30 mm) after previous loading with increasing concentrations of either BAPTA-AM or EGTA-AM in either plus or minus Ca²⁺ medium. A representativetrace of the subsequent Ca²⁺-dependent release of loaded FM2–10 (S2) by a standard stimulus of 30 mm KCl is displayed. In all experiments, either BAPTA-AM or EGTA-AM were preincubated with the synaptosomes for 30 min before stimulation. KCl stimulation is represented by the bar; n = 4.E, KCl-stimulated retrieval efficiency in BAPTA-AM- (triangles) and EGTA-AM- (squares) loaded synaptosomes. Exocytosis was constant during S2 stimulation for EGTA-AM-loaded synaptosomes but was greatly reduced for BAPTA-AM-loaded synaptosomes (data not shown). Therefore, retrieval efficiency is an underestimate with respect to BAPTA-AM-loaded synaptosomes. For all experiments, n = 3–4 (±SEM). Error bars are smaller than the symbols.