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. 2016 Oct;148(4):341–355. doi: 10.1085/jgp.201611604

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© 2016 Tsukamoto et al.

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Figure 6. — Effects of ISO on local coupling of [Ca²⁺]_i and SL dynamics. (A) Individual data showing time courses of changes in F_yellow/F_cyan (top) and SL (bottom) in α-actinin–YC-Nano140–expressing cardiomyocytes during spontaneous beating in the absence (left; indicated as “control”) and presence (right) of 50 nM ISO. n = 7 and 9 in the absence and presence of ISO, respectively. Experiments were performed at 37°C. (B) Individual data showing the relationship of F_yellow/F_cyan versus SL in the absence and presence of ISO. A closed loop-like trajectory was observed, regardless of the use of ISO (compare Butler et al., 2015). (C) Comparison of F_yellow/F_cyan values during relaxation (R₀) and contraction (R_max) in the absence and presence of ISO. F_yellow/F_cyan was significantly higher for both R₀ and R_max. (D) Comparison of ΔR/R₀ in the absence and presence of ISO (see Fig. 2 for ΔR/R₀). (E) SL values in the absence and presence of ISO, during relaxation and contraction. ISO did not significantly affect SL, regardless of the contractile state. (F) ΔSL (difference between SL at relaxation and contraction) values in the absence and presence of ISO. No significant difference was observed between groups. Likewise, the variance was similar for both groups (i.e., from ∼0.03 to ∼0.17 µm for control [difference, ∼0.14 µm] and from ∼0.03 to ∼0.15 µm for ISO [difference, ∼0.12 µm]). (G) Shortening velocity of SL dynamics in the absence and presence of ISO. The velocity became significantly faster in the presence of ISO. (H) Lengthening velocity of SL dynamics in the absence and presence of ISO. (I) Time to peak values for changes in F_yellow/F_cyan and SL in the absence and presence of ISO. The values were less for both parameters, indicating the acceleration of the EC coupling at the single sarcomere level. (J) Comparison of the decay time for F_yellow/F_cyan. The time was shorter in the presence of ISO, indicating enhanced removal of cytosolic [Ca²⁺]_i, presumably via acceleration of SR Ca²⁺ pump coupled with PLN phosphorylation (see Bers [2001] and references therein). In all graphs, horizontal bars indicate mean values. *, P < 0.05; **, P < 0.01; and ***, P < 0.001 (Mann-Whitney U test).