In vivo tracking of individual sarcomeres along a myofibril in an LV myocyte. (A) Confocal image of a myocyte expressing α-actinin-AcGFP. Note clear striation patterns along myofibrils. In the yellow-outlined rectangle (M1), 30 sequentially connected sarcomeres in a myofibril were analyzed. Numbers on top of the myofibril indicate longitudinal positions of sarcomeres (i.e., nos. 1–30). Scale bar, 10 µm. See Video 2. (B) Time course of changes in average SL (top) and LVP (bottom) during six cardiac cycles (cardiac cycle determined based on LVP recording). Average SL indicates the average of the lengths of 30 sarcomeres in M1. During six cardiac cycles, HR was 469 ± 2.9 bpm, and ΔLVP (systolic LVP minus diastolic LVP) was 96.4 ± 4.7 mm Hg. Error bars for average SL indicate the SD of 30 sarcomeres. (C) Time course of changes in the lengths of sarcomere nos. 1–30 (from top downward for sarcomere nos. 1–30; see right) in M1. Note that large, abrupt length changes (e.g., in sarcomere no. 20) are due to irregular movements of the target myocyte and do not reflect SL changes. (D) Typical examples of scatter plots showing a positive correlation (no. 1), no correlation (no. 8), and a negative correlation (no. 20) between changes in average and individual SLs during six cardiac cycles in B. CI values are 0.59, 0.06, and −0.17 for nos. 1, 8, and 20, respectively. See Fig. S5 for data on all sarcomeres. (E) Triangular heat map showing correlation between average and individual SLs (top row) and between an individual sarcomere and other sarcomeres in M1 (second row and below). Sarcomere number (i.e., from nos. 1 to 30; or average) is indicated on top and at the left end of each row. CI is illustrated on a color scale, as indicated on right (i.e., from 1 [dark blue] to −1 [dark red]). (F) Color diagram showing CI between average and individual SLs from nos. 1 to 30 during six cardiac cycles for M1. Sarcomere numbers are indicated on top, and cardiac cycle numbers on left. Bottom: Average of six cycles (i.e., same as top row in E). Arrows indicate sarcomeres at nos. 6, 18, and 25 showing marked changes in CI during consecutive cardiac cycles.
Figure 1.

In vivo tracking of individual sarcomeres along a myofibril in an LV myocyte. (A) Confocal image of a myocyte expressing α-actinin-AcGFP. Note clear striation patterns along myofibrils. In the yellow-outlined rectangle (M1), 30 sequentially connected sarcomeres in a myofibril were analyzed. Numbers on top of the myofibril indicate longitudinal positions of sarcomeres (i.e., nos. 1–30). Scale bar, 10 µm. See Video 2. (B) Time course of changes in average SL (top) and LVP (bottom) during six cardiac cycles (cardiac cycle determined based on LVP recording). Average SL indicates the average of the lengths of 30 sarcomeres in M1. During six cardiac cycles, HR was 469 ± 2.9 bpm, and ΔLVP (systolic LVP minus diastolic LVP) was 96.4 ± 4.7 mm Hg. Error bars for average SL indicate the SD of 30 sarcomeres. (C) Time course of changes in the lengths of sarcomere nos. 1–30 (from top downward for sarcomere nos. 1–30; see right) in M1. Note that large, abrupt length changes (e.g., in sarcomere no. 20) are due to irregular movements of the target myocyte and do not reflect SL changes. (D) Typical examples of scatter plots showing a positive correlation (no. 1), no correlation (no. 8), and a negative correlation (no. 20) between changes in average and individual SLs during six cardiac cycles in B. CI values are 0.59, 0.06, and −0.17 for nos. 1, 8, and 20, respectively. See Fig. S5 for data on all sarcomeres. (E) Triangular heat map showing correlation between average and individual SLs (top row) and between an individual sarcomere and other sarcomeres in M1 (second row and below). Sarcomere number (i.e., from nos. 1 to 30; or average) is indicated on top and at the left end of each row. CI is illustrated on a color scale, as indicated on right (i.e., from 1 [dark blue] to −1 [dark red]). (F) Color diagram showing CI between average and individual SLs from nos. 1 to 30 during six cardiac cycles for M1. Sarcomere numbers are indicated on top, and cardiac cycle numbers on left. Bottom: Average of six cycles (i.e., same as top row in E). Arrows indicate sarcomeres at nos. 6, 18, and 25 showing marked changes in CI during consecutive cardiac cycles.

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