Graph A: Peak Passive Stress. This line graph displays the Peak Passive Stress of the cardiac fibers. The horizontal axis represents Sarcomere Length in micrometers, ranging from 1.8 to 2.3 micrometers with increments of 0.1 micrometers. The vertical axis represents Stress in milliNewtons per square millimeter, ranging from 0 to 10 with increments of 2. Two upward-curving lines are shown: a gray W T line and a blue mutant line. Both lines start near 0.2 millinewtons per square millimetre at a length of 1.85 micrometers. The blue line rises slightly higher than the gray line as the sarcomere is stretched, reaching approximately 8 millinewtons per square millimetre at the final length of 2.32 micrometers, while the W T reaches roughly 7.2 millinewtons per square millimetre. The difference between these curves is statistically significant, labeled as p equals 0.0057. Graph B: Elastic Stress. This graph illustrates the Elastic Stress component of the cardiac fibers. The horizontal and vertical axes, ranges, and increments are identical to Graph A. The gray W T line and blue mutant line follow a similar upward trend as the peak stress. The blue mutant line consistently maintains a slightly higher position than the gray line throughout the stretch. At the maximum sarcomere length of 2.32 micrometers, the elastic stress is approximately 6 millinewtons per square millimetre for the mutant and 5 millinewtons per square millimetre for the W T. The statistical significance for the difference between these two curves is noted as p equals 0.0005. Graph C: Viscous Stress. This graph displays the Viscous Stress component, which reflects the internal resistance of the cardiac muscle during stretch. The horizontal and vertical axes remain on the same scale as the previous two graphs. Both the gray W T line and the blue mutant line remain quite low compared to peak or elastic stress, staying below 1 millinewtons per square millimetre until the sarcomere length exceeds 2.1 micrometers. At the final stretch point of 2.32 micrometers, both lines reach approximately 2.5 millinewtons per square millimetre, with the blue line overlapping or sitting marginally above the gray line. The curve difference is labeled p greater than 0.05, indicating that there is no statistically significant difference in viscous stress between the wild-type and mutant cardiac fibers. Panel D: Maximal Active Stress. This bar graph illustrates the Maximal Active Stress generated by cardiac muscle fibers. The vertical axis represents Stress measured in milliNewtons per square millimeter, ranging from 0 to 80 with increments of 20. The horizontal axis compares the WT group (gray bar) and the Ttn Delta A164-167 group (blue bar). Both bars reach a nearly identical mean height of approximately 32 milliNewtons per square millimeter. Numerous individual data points are scattered over both bars, and error bars indicate the standard deviation. A bracket at the top labeled ns confirms that there is no statistically significant difference in maximal active stress production between the wild-type and mutant cardiac fibers. Panel E: Stress-Calcium Relationship. This panel features a sigmoid line graph showing the relationship between free calcium and muscle stress, with an inset quantifying calcium sensitivity. Main Graph: The horizontal axis represents Free Calcium concentration measured in micromolar on a logarithmic scale ranging from 0.1 to 100. The vertical axis represents Stress in milliNewtons per square millimeter, ranging from 0 to 40 with increments of 10. The gray line (W T) and blue line (Ttn Delta A164-167) follow almost identical paths, rising sharply between 1 micromolar and 10 micromolar before plateauing at a maximum stress of approximately 31 milliNewtons per square millimeter. Inset Graph (Ca 2 plus E C 50): This bar graph shows the concentration of calcium required to reach 50 percent maximal stress. The vertical axis is measured in micromolar from 0 to 4. Both the gray W T bar and the blue mutant bar plateau at a mean value of approximately 2.2 micromolar. A bracket labeled ns indicates that there is no statistically significant difference in cardiac calcium sensitivity between the two genotypes. All values are approximate.
Cardiomyocyte mechanics. (A) Peak stress generated by cardiomyocytes passively stretched to a range of sarcomere lengths. (B) Elastic component of passive stress. (C) Viscous component of passive stress. Statistical significance for A–C was determined by mixed-effects analysis at each sarcomere length (no significance found) and exponential growth curve fitting with an extra sum-of-squares F test (P value on plot). 6 WT and 6 TtnΔA164–167 mice were used, with 6 cells tested per animal. (D) Maximal active stress measurements from individual cardiomyocytes. Four animals per genotype were used, with six cells tested per animal. Statistical significance was determined by nested t test (nested by mouse). (E) Stress–Ca2+ relationship, with EC50 measured in individual cell inset. The stress–Ca2+ curve was fit with a Hill equation, and statistical significance of curve fit was determined by an extra sum-of-squares F test. Statistical significance of EC50 was determined by a nested t test (nested by mouse). 4 WT and 4 TtnΔA164–167 mice were used, with 3–4 cells tested per mouse.