Figure 2.

Uptake of large dextrans only occurs during strong action potential stimulation. Left, Representative fields in which tetramethylrhodamine-dextran (50 μm) was applied to cultures during trains of 200 (A; 10 Hz), 400 (C; 40 Hz), or 800 (E; 80 Hz) action potentials and then immediately washed away. Right, Fields in which dextran was applied to cultures for 2 min immediately after trains of 200 (B; 10 Hz), 400 (D; 40 Hz), or 800 (F; 80 Hz) action potentials. Scale bar, 15 μm. Mean number of dextran puncta per field ± SEM is displayed for either during (G; open bars) or after (H; hatched bars) stimulation. Dotted line illustrates puncta number per field attributable to intrinsic background fluorescence in the absence of dextran. All experiments were performed three times. ***p < 0.001, one-way ANOVA.