In vivo tracking of individual sarcomeres along parallel myofibrils in an LV myocyte. (A) Confocal image of a myocyte expressing α-actinin-AcGFP (same as in Fig. 1 A). 30 sarcomeres, in yellow-outlined rectangles, were analyzed for M1 and M2 were analyzed. Scale bar, 10 µm. See Video 2. (B) Top: Time course of changes in the lengths of averaged 30 sarcomeres (left), and examples of sarcomeres at the same longitudinal positions showing a positive correlation (middle, no. 2) or a negative correlation (right, no. 20). Data were obtained from six cardiac cycles. Black line, M1; blue line, M2. Average diastolic and systolic SLs for M1 were 1.85 ± 0.02 µm and 1.70 ± 0.04 µm, respectively (as in text; see Fig. 2, B–E, for plots of 30 sarcomeres). Average diastolic and systolic SLs for M2 were 1.77 ± 0.02 µm and 1.66 ± 0.02 µm, respectively. Average shortening ratios were 8.0% and 6.5% for M1 and M2, respectively (compare Kobirumaki-Shimozawa et al., 2016). Bottom: Scatter plots for dynamics between sarcomeres in M1 (x axis) and M2 (y axis). Left: Averaged 30 sarcomeres (CI, 0.82); middle, sarcomeres at no. 2 (CI, 0.46); right, sarcomeres at no. 20 (CI, −0.18). (C) Triangular heat map showing correlation between the average of 30 sarcomeres in M1 and each sarcomere in M2 or the average of 30 sarcomeres in M2 (right end). Sarcomere numbers are indicated on top. Underlying rows show correlations between sarcomere nos. 1–30 in M1 and each sarcomere in M2, or the average of 30 sarcomeres in M2. In this diagram, CI is displayed on a color scale, as indicated on right (i.e., from 1 [dark blue] to −1 [dark red]). (D) Color diagram showing CI between sarcomeres in M1 and M2 at the same longitudinal positions during six cardiac cycles. Sarcomere numbers are indicated on top. The diagram on bottom indicates average CI along myofibrils during six cardiac cycles. Data for M1 are the same as in Fig. 1 F. (E) Top: Illustration showing the numbering of sarcomeres in M1 and M2. In this analysis, six positions (i.e., 0–5) in M2 in relation to M1 are defined. Position 0 is defined as the same longitudinal position along M2. Position 1 is adjacent to position 0 on both sides, and positions 2–5 are defined as illustrated. Bottom left: Graph showing CI for sarcomeres located at positions 0–5 in M2. *, P < 0.05 compared with position 0. Bottom right: Relationship between average CI for individual sarcomeres along M1 (x axis) and CI at position 0 in M2 (y axis). A significant linear relationship was present (R = 0.51; P < 0.01). (F) Top: Illustration showing the numbering of sarcomeres in a myofibril (either M1 or M2). In this analysis, seven positions (i.e., 0–6) in series are defined. Position 1 is adjacent to position 0 on both sides, and positions 2–6 are defined as illustrated. Bottom left: Graph showing CI for sarcomeres located at positions 1–6. Data from M1 and M2 are pooled. *, P < 0.05; ***, P < 0.001 compared with position 1. Bottom right: Relationship between average CI for individual sarcomeres along a myofibril (x axis) and CI between neighboring sarcomeres (i.e., at positions 0 and 1; y axis). A significant linear relationship was present (R = 0.50; P < 0.001). Data from M1 and M2 are pooled in this graph. In B–D and F, Avg. indicates average.
Figure 3.

In vivo tracking of individual sarcomeres along parallel myofibrils in an LV myocyte. (A) Confocal image of a myocyte expressing α-actinin-AcGFP (same as in Fig. 1 A). 30 sarcomeres, in yellow-outlined rectangles, were analyzed for M1 and M2 were analyzed. Scale bar, 10 µm. See Video 2. (B) Top: Time course of changes in the lengths of averaged 30 sarcomeres (left), and examples of sarcomeres at the same longitudinal positions showing a positive correlation (middle, no. 2) or a negative correlation (right, no. 20). Data were obtained from six cardiac cycles. Black line, M1; blue line, M2. Average diastolic and systolic SLs for M1 were 1.85 ± 0.02 µm and 1.70 ± 0.04 µm, respectively (as in text; see Fig. 2, B–E, for plots of 30 sarcomeres). Average diastolic and systolic SLs for M2 were 1.77 ± 0.02 µm and 1.66 ± 0.02 µm, respectively. Average shortening ratios were 8.0% and 6.5% for M1 and M2, respectively (compare Kobirumaki-Shimozawa et al., 2016). Bottom: Scatter plots for dynamics between sarcomeres in M1 (x axis) and M2 (y axis). Left: Averaged 30 sarcomeres (CI, 0.82); middle, sarcomeres at no. 2 (CI, 0.46); right, sarcomeres at no. 20 (CI, −0.18). (C) Triangular heat map showing correlation between the average of 30 sarcomeres in M1 and each sarcomere in M2 or the average of 30 sarcomeres in M2 (right end). Sarcomere numbers are indicated on top. Underlying rows show correlations between sarcomere nos. 1–30 in M1 and each sarcomere in M2, or the average of 30 sarcomeres in M2. In this diagram, CI is displayed on a color scale, as indicated on right (i.e., from 1 [dark blue] to −1 [dark red]). (D) Color diagram showing CI between sarcomeres in M1 and M2 at the same longitudinal positions during six cardiac cycles. Sarcomere numbers are indicated on top. The diagram on bottom indicates average CI along myofibrils during six cardiac cycles. Data for M1 are the same as in Fig. 1 F. (E) Top: Illustration showing the numbering of sarcomeres in M1 and M2. In this analysis, six positions (i.e., 0–5) in M2 in relation to M1 are defined. Position 0 is defined as the same longitudinal position along M2. Position 1 is adjacent to position 0 on both sides, and positions 2–5 are defined as illustrated. Bottom left: Graph showing CI for sarcomeres located at positions 0–5 in M2. *, P < 0.05 compared with position 0. Bottom right: Relationship between average CI for individual sarcomeres along M1 (x axis) and CI at position 0 in M2 (y axis). A significant linear relationship was present (R = 0.51; P < 0.01). (F) Top: Illustration showing the numbering of sarcomeres in a myofibril (either M1 or M2). In this analysis, seven positions (i.e., 0–6) in series are defined. Position 1 is adjacent to position 0 on both sides, and positions 2–6 are defined as illustrated. Bottom left: Graph showing CI for sarcomeres located at positions 1–6. Data from M1 and M2 are pooled. *, P < 0.05; ***, P < 0.001 compared with position 1. Bottom right: Relationship between average CI for individual sarcomeres along a myofibril (x axis) and CI between neighboring sarcomeres (i.e., at positions 0 and 1; y axis). A significant linear relationship was present (R = 0.50; P < 0.001). Data from M1 and M2 are pooled in this graph. In B–D and F, Avg. indicates average.

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