Figure 2.

RyR2 regulation by luminal Ca²⁺ and Mg²⁺. (A) Single channel recordings of RyR2 from healthy human heart with luminal [Ca²⁺] indicated to the left of each trace. Channel recordings were taken in the presence of 100 nM cytoplasmic Ca²⁺ (pCa 7) and 2 mM ATP in the cytoplasm at −40 mV. Channel openings are downward current jumps from the baseline (arrows). (B) Effect of luminal Ca²⁺ on RyR2 P_o from human, sheep, and rat as indicated in the legend (legend also applies to D). The luminal [Ca²⁺] activation response of RyR2 was obtained using cytoplasmic pCa 7 and 2 mM ATP. (C) P_o of RyR2 from human, sheep, and rat in the presence of various combinations of cytoplasmic and luminal [Ca²⁺]. Asterisks indicate significant difference to luminal pCa 9 (*, P < 0.05). (D) Luminal [Mg²⁺] inhibition response of RyR2 with cytoplasmic pCa 7 (2 mM ATP) and luminal pCa 4. The solid and dashed curves show Hill fits to the data. The number of experiments and the Hill parameters for rat and sheep RyR2 are listed in Table 3. Data points show the mean ± SEM. Data for rat RyR2 in B and D were obtained from Li et al. (2013).