FIGURE 6.

RyR expression and SOICR in HEK293 cells expressing RyR2 and the N-RyR2/C-RyR1 chimera. (A) Western blot analysis of RyR proteins in HEK293 cells expressing RyR2 or the N-RyR2/C-RyR1 chimera. HEK293 cells containing the RyR2 gene were induced by tetracycline for different lengths of time, whereas cells containing the chimera gene were induced for 24 h. RyR proteins from the same amount of cell lysate were immunoblotted with anti-RyR antibody. (B and C) Fura-2 ratio of single RyR2 cells induced for 12 h (B) and of single N-RyR2/C-RyR1 cells induced for 24 h (C) at elevated [Ca²⁺]_o. (D) The fraction (%, mean ± SE) of RyR2 cells (12 h induction, open circle) and N-RyR2/C-RyR1 (24 h induction, solid circle) that display Ca²⁺ oscillations at various [Ca²⁺]_o. The total numbers of cells analyzed for Ca²⁺ oscillations were 436 (RyR2, 12 h) and 876 (N-RyR2/C-RyR1, 24 h) from five to eight separate experiments. (E) Store Ca²⁺ content in HEK293 cells expressing N-RyR1/C-RyR2 induced for 6 h or in HEK293 cells expressing N-RyR2/C-RyR1 induced for 24 h at various [Ca²⁺]_o was estimated by measuring the amplitude of caffeine (5 mM)-induced Ca²⁺ release and normalized to the maximum level obtained at 10 mM [Ca²⁺]_o. Data shown represent the mean ± SE from four separate experiments.