Figure 5.

The G4955E mutation markedly increases the channel sensitivity to luminal Ca²⁺activation. Recombinant RyR2 WT and G4955E mutant channels were partially purified from cell lysate prepared from HEK293 cells transiently transfected with the RyR2 WT or G4955E mutant complementary DNA. Single-channel activities were recorded in a symmetrical recording solution containing 250 mM KCl and 25 mM Hepes (pH 7.4). Representative current traces of single RyR2 WT (A) and G4955E (B) channels in the presence of different cytosolic Ca²⁺ concentrations and 45 nM luminal Ca²⁺ (panels a and b) and in the presence of 45 nM cytosolic Ca²⁺ and different luminal Ca²⁺ concentrations (panels c and d). The open probability of RyR2 WT or G4955E channels activated by various fixed cytosolic Ca²⁺ (C) or fixed luminal Ca²⁺ concentrations (D). The frequency of open events of single RyR2 WT or G4955E mutant channels in the presence of 45 nM cytosolic and 45 nM luminal Ca²⁺ concentration (E). Data shown are mean ± SD from seven RyR2 WT and seven G4955E single channels. ∗∗p < 0.01 versus WT. HEK293, human embryonic kidney 293 cells; RyR2, cardiac ryanodine receptor.