Figure 7. High Cl⁻ Inhibits Endocytosis in Terminals from the Slice Treated with 50 µM External PTX under 5 mM Internal EGTA.

(A) At 0.5 mM internal EGTA, Ca²⁺-activated chloride tail currents [I_Cl(Ca)] are present under both high- (blue) and low (red)-chloride internal solutions in the PTX-treated slice (arrow on inset). As in the dissociated terminals, endocytosis has both a fast and slow component with 15 mM internal Cl⁻ (red C_m trace). However, at 125 mM internal Cl⁻ endocytosis has no fast component (blue C_m trace) and is well fit with slower, single exponentials.

(B) At 5 mM internal EGTA, endocytosis remains fast in PTX-treated slices under low internal Cl⁻ (red C_m trace), and I_Cl(Ca) is nearly completely abolished (arrow on inset). Note that high EGTA does not slow endocytosis per se. At 125 mM internal Cl⁻ and 5 mM EGTA, endocytosis in PTX-treated slices again has no fast component (blue C_m trace) and can be fit with a slow, single exponential.