Figure 2.

The observed spatial profile of Ca²⁺ influx is dependent on the timing of the laser illumination window. A, Representative difference image of Ca²⁺ entry with an illumination window of 1 msec duration beginning 1.5 msec after nerve trunk stimulation. B, Representative difference image of Ca²⁺ entry with an illumination window of 2 msec duration beginning 1.5 msec after nerve stimulation. The Ca²⁺ entry signal is more intense (resulting from a doubling in the dye illumination time) but also more diffusely distributed throughout the nerve terminal. C, Representative raw difference image of Ca²⁺ entry with an illumination window of 1 msec duration beginning 12 msec after nerve stimulation. The Ca²⁺ entry signal is slightly reduced in magnitude as compared with A and much more diffusely distributed. The timing of the illumination window is shown schematically in each image. The pseudocolor scale bar is the same for all panels and is expressed as ΔF/F (%). Scale bar, 2 μm.