Figure 1.

A, B, The rate of decay of synaptopHluorin (A) and vGlut-pHluorin (B) fluorescence after action potential stimulation reaches a limiting value during a prolonged stimulus. The lines in A and B are the fluorescence response of synaptopHluorin- and vGpH-transfected synaptic boutons, respectively, that are subject to varying duration of stimulus (50, 70, 100, 150, 200, 300, 400, and 500 AP at 10 Hz for spH; 50, 75, 100, 150, 200, 250, and 300 at 10 Hz AP for vGpH). The peak of the pHluorin response is proportional to surface accumulation of the vesicular membrane at the end of the stimulus. The dashed curves are the response of the same set of boutons for action potentials fired at 33 Hz for 10 s, which provides a measure of the total recycling pool.