Figure 2. Classification of cells depending on the time constants of peak amplitude decay of Ca²⁺ spikes.

Representative traces of Indo-5F signal changes (F/F₀; top) and IRIS-1 signal changes (ΔR/R₀; bottom) in cells showing sustained Ca²⁺ oscillations (S-cell) (A) and damped oscillations (D-cell) (B). Three different concentrations of histamine (1, 3, and 10 µM) were sequentially applied to the same cells with an interval of 20 min. (C) Relationships between the histamine concentrations and the inverse time constants of Ca²⁺ amplitude decay in S-cells (red) and D-cells (blue). (D) Relationships between the histamine concentrations and the Ca²⁺ oscillation frequencies observed in S-cells (red) and D-cells (blue). (E–G) Comparisons of the Ca²⁺ oscillation frequencies between S-cells (red) and D-cells (blue). The histamine concentrations were 1 µM (E), 3 µM (F), and 10 µM (G). (H–J) Comparisons of integrated IRIS-1 signals between S-cells (red) and D-cells (blue). The histamine concentrations were 1 µM (H), 3 µM (I), and 10 µM (J).