Fig. 2

H₂O₂-mediated facilitation of Ca²⁺ channel activity in inside-out mode. a, c Time course of channel activity (NPo) recorded in the cell-attached (c.a.) mode followed by the inside-out (i.o.) mode, in which channel activity was maintained with 1 μM CaM + 3 mM ATP, and then 1 mM H₂O₂ without (a) or with (c); 10 μM KN-93 was additionally applied as indicated by the boxes in each graph. ATP was included throughout the experiments in the i.o mode. b Concentration-dependent effect of H₂O₂. Normalized channel activity was plotted against concentration of H₂O₂. Data (n = 4–6) were fitted with a combined Hill’s equation as: \( (100 + A \cdot [{\text{H}}_{2} {\text{O}}_{2} ]^{{n_{\text{f}} }}/({\text{Kd}}_{\text{f}}^{{n_{\text{f}} }} + [{\text{H}}_{2} {\text{O}}_{2} ]^{{n_{\text{f}} }} )) \cdot ({\text{Kd}}_{\text{i}}^{{n_{\text{i}} }} /({\text{Kd}}_{\text{i}}^{{n_{\text{i}} }} + [{\text{H}}_{2} {\text{O}}_{2} ]^{{n_{\text{i}} }} )) \), where [H₂O₂] was the concentration of H₂O₂, A the extent of facilitation, Kd_f and Kd_i apparent dissociation constants, and n _f and n _i Hill’s numbers for facilitation and inhibition, respectively. The fitted curve was drawn with A = 147, Kd_f = 0.68 mM, n _f = 2, Kd_i = 3.11 mM, and n _i = 3 (r ² = 0.983). d Summary of the normalized channel activity in the presence of CaM + ATP in i.o. mode before and after addition of H₂O₂ ± KN-93 (n = 5–6). Data are shown as mean ± SE. *P < 0.05 versus CaM (t test), NS not significant (ANOVA)