Figure 5.

Effects of caffeine, ATP, and Mg²⁺ on RyR1-WT and E3893Q/E3967Q and E3893V/E3967V variant channel open probabilities in the absence of cytosolic Ca²⁺. A and C, representative single-channel currents are shown at −20 mV as downward deflections from the closed state (c−) in symmetrical 0.25 m KCl with 2 μm SR luminal Ca²⁺, 0.01 μm cytosolic Ca²⁺, and the indicated sequential additions of caffeine and ATP (A) and Mg²⁺ (C). B, -fold increase of normalized P_o after the addition of caffeine (●, +C) and 5 mm caffeine plus 2 mm ATP (○, +C/A). D, -fold decrease of P_o after the addition of 0.25 mm Mg²⁺. B and D, data are the mean ± S.E. (error bars) of 4–6 experiments. *, p < 0.05 compared with respective controls by two-way ANOVA followed by the Holm–Sidak method (B) and Student's t test (D).