FIGURE 4.

Factors affecting the spatial extent of Ca²⁺ release waves following uncaging or synaptic stimulation. (A and B) Representative examples of Ca²⁺ release evoked by pairing large and small subthreshold UV flashes with a single bAP. (C) Average Ca²⁺ wave extent in three kinds of experiments; large spot: 89 ± 2 μm, n = 5 cells, 12 trials; small spot: 34±2 μm, n = 18 cells, 21 trials; synaptic stimulation: 44 ± 2 μm, n = 3 cells, 31 trials; wave extent measured at 50% of peak amplitude. The three sizes were significantly different but the synaptic size was closer to the small spot size (F (2, 61) = 85.7, P < 0.01, ANOVA). Asterisk shows significance (P < 0.05) by Tukey post-hoc test. In A and B arrows (a) are the times of single bAPs. The arrows (b) are the times of the bAP paired with the uncaging flash. (D) One example of secondary Ca²⁺ waves generated at the end of a 2 s long uncaging pulse. The secondary waves always extended further along the dendrite. A possible explanation for why two secondary waves were always generated is that the IP₃ receptors in the center were desensitized by the high concentration of released IP₃ in this region, but we do not have direct evidence to support this hypothesis. (E) Summary histogram of the spatial extents of the primary and secondary waves (n=8).