Cytosolic Ca²⁺ action on single RyR2 function. (A) Representative single-channel currents from WT (left) and K4750Q (right) channels. Openings are upward from the basal current level. (B) Summary of Po dependence on cytosolic Ca²⁺. WT (black open circles), K4750Q (red filled circles), R2473S (green filled circles), and native RyR2 (black open squares). n = 9 (WT), 6 (K4750Q), 6 (R2473S), and 4 (native RyR2). **, P < 0.01 versus WT. Values shown are mean ± SEM.