Figure 4. IP₃-evoked [Ca²⁺]_c increases.

At −70 mV, locally photolyzed caged IP₃ (↑, 2 μm diameter region; position indicated by the spots in A right-hand panel) at the two peripheral regions of the cell separately (Ci & Cii) increased [Ca²⁺]_c (B,C) which was maximal at and decreased away from the release site. When IP₃ was released by photolysis at both sites almost simultaneously (2 ms apart; ↑, Ciii) the Ca²⁺ increase at the point of Ca²⁺ contact (region 3, green line) approximately doubled in amplitude. The result is consistent with the passive diffusion of Ca²⁺ from the release site. The [Ca²⁺]_c images (B) are derived from the time points indicated by the corresponding numerals in C. [Ca²⁺]_c changes in B are represented by colour; blue low and red/white high [Ca²⁺]_c. Changes in the fluorescence ratio with time (C) are derived from the boxes shown in A centre panel ( regions 1-3). (A) left panel shows a bright field image of the cell; see also whole cell electrode (right side). The spike in fluorescence on uncaging (↑) arises from the light flash used to uncage IP₃.