Figure 2.

Time course of FRET signals of various α-actinin–YC-Nanos. (A) Time course of changes in F_yellow/F_cyan during spontaneous beating in myocytes expressing α-actinin–YC-Nano15, α-actinin–YC-Nano50, α-actinin–YC-Nano65, or α-actinin–YC-Nano140 in the Z disks. n = 4–12 cells. For strong possible fluorescence signal recordings, measurements were performed in 2.0 mM Ca²⁺-HEPES–Tyrode’s solution at 37°C. See Video 2. (B) Maximal (R_max) and minimal (R₀) FRET signals for α-actinin–YC-Nano15, α-actinin–YC-Nano50, α-actinin–YC-Nano65, and α-actinin–YC-Nano140 expressed in the Z disks of myocytes during spontaneous beating (data obtained for 5 s as in A). Closed symbols, R₀; open symbols, R_max. (C) Values of ΔR (i.e., R_max − R₀) for α-actinin–YC-Nanos. Data obtained from A and B. No significant differences were observed between groups (Tukey-Kramer test). (D) Values of the ratio of ΔR to R₀ (i.e., ΔR/R₀) for α-actinin–YC-Nanos. **, P < 0.01; and ***, P < 0.001 compared with α-actinin-YC-Nano140 (Tukey-Kramer test). Note that in D, ΔR/R₀ was highest for α-actinin–YC-Nano140, followed by α-actinin–YC-Nano65, α-actinin–YC-Nano50, and α-actinin–YC-nano15, suggesting that among the α-actinin–YC-Nano complexes tested, α-actinin–YC-Nano140 is most sensitive to a change in local [Ca²⁺]_i at Z disks in cardiomyocytes, and hence it is the most ideal for the simultaneous investigation of local Ca²⁺ dynamics and SL displacement. Bars in each graph indicate mean values.