Fig. 4.

Effects of caffeine and ATP on type 1 ryanodine receptor- wild type (RyR1-WT) and mutant channel open probabilities (P_o). A–C: representative single-channel currents of RyR1-WT (A), RyR1-Q3970E (B), and RyR1-Q3970K (C) were recorded as downward deflections from the closed state (C–) in 250 mM symmetrical KCl at −20 mV. Luminal Ca²⁺ was 2 µM. Cytosolic solutions contained 30 µM Ca²⁺ (top traces), 30 µM Ca²⁺ and 5 mM caffeine (middle traces), and 30 µM Ca²⁺, 5 mM caffeine, and 2 mM ATP (bottom traces). Free Ca²⁺ was 5 µM in the presence of 5 mM caffeine and 2 mM ATP as described under materials and methods. D: channel open probability in the presence of 30 µM cytoplasmic Ca²⁺ (open symbols), 30 µM Ca²⁺ and 5 mM caffeine (shaded symbols), and 5 µM Ca²⁺ plus 5 mM caffeine and 2 mM ATP (closed symbols). Data are the mean ± SE of 3–6 recordings. *P < 0.05 compared with respective controls by one-way ANOVA followed by Tukey’s test. [WT data in D were obtained from Xu et al. (31) under recording conditions used in the present report.]