Figure 3.
Graph A: Peak Passive Stress: This line graph illustrates the Peak Passive Stress of the muscle fibers. The horizontal axis represents Sarcomere Length measured in micrometers, ranging from 2.4 to 3.6 micrometers with increments of 0.2 micrometers. The vertical axis represents Stress measured in milliNewtons per square millimeter, ranging from 0 to 80 with increments of 20. The graph displays two upward-curving lines: a gray line for W T and a blue line for Ttn Delta A164-167. Both lines start near 0 milliNewtons per square millimeter at a length of 2.5 micrometers. As length increases, the blue mutant line rises more steeply than the gray W T line. The overall curve difference is noted as p less than 0.0001. Graph B: Elastic Passive Stress. This graph shows the Elastic Passive Stress component, which represents the force that returns to baseline after a stretch. The axes, ranges, and increments are identical to Graph A, with the horizontal axis in micrometers and the vertical axis in milliNewtons per square millimeter. Two lines are plotted: a gray W T line and a blue mutant line. Similar to the peak stress, the lines diverge as the sarcomere is stretched beyond 3.0 micrometers. The blue line consistently sits above the gray line, reaching a maximum of approximately 40 Millinewtons per square millimetre at a length of 3.6 micrometers, compared to roughly 28 Millinewtons per square millimetre for the W T. Statistical significance is indicated at the 3.5 and 3.6 micrometers marks with asterisks, and the curve difference is labeled p less than 0.0001. Graph C: Viscous Passive Stress represents the Viscous Passive Stress, which accounts for the internal friction or decay of force within the muscle during stretch. The horizontal axis (Sarcomere Length in micrometers) and vertical axis (Stress in milliNewtons per square millimeter) maintain the same scales as the previous graphs. Both the gray W T line and the blue mutant line show much lower values here than in the peak or elastic graphs. Both lines stay near 0 millinewtons per square millimetre until roughly 3.2 micrometers. At the maximum stretch of 3.6 micrometers, the stress for both groups is low, with the mutant line at approximately 12 Millinewtons per square millimetre and the WT line at approximately 8 Millinewtons per square millimetre. While the blue line is slightly higher, the statistical difference between these curves is noted as p less than 0.0001. Graph D: Active Stress. This bar graph displays the Active Stress generated by the muscle fibers. The vertical axis represents Stress, measured in millinewtons per square millimeter, with a range of 0 to 300 and increments of 100. The horizontal axis identifies the two groups: W T (represented by a gray bar) and Ttn Delta A164-167 (represented by a blue bar). Both bars reach an average height of approximately 160 millinewtons per square millimeter. Numerous individual data points are plotted as dots over both bars, and error bars indicate the standard deviation. A bracket at the top is labeled ns (not significant), indicating that there is no statistical difference in active stress production between the two genotypes. Graph E: Cross-sectional area (C S A): This bar graph compares the Cross-sectional area of the individual muscle fibers. The vertical axis represents C S A measured in square millimeters, ranging from 0.0000 to 0.0025 with increments of 0.0005. The W T group (gray bar) has an average C S A of approximately 0.0017 square millimeters, while the Ttn Delta A164-167 group (blue bar) is visibly lower with an average of approximately 0.0012 square millimeters. Individual data points show a clear downward shift in the mutant group. A bracket above the bars is marked with two asterisks, signifying a statistically significant decrease in fiber size in the mutant mice compared to the wild-type. Graph F: K tr (Rate of Tension Redevelopment). This bar graph illustrates the K tr, which measures the rate of tension redevelopment in the fibers. The vertical axis represents K tr measured in reciprocal seconds, ranging from 0 to 15 with increments of 5. The WT gray bar and the Ttn Delta A164-167 blue bar both plateau at a mean value of approximately 9 reciprocal seconds. The distribution of individual data points and the standard deviation error bars are nearly identical for both groups. The graph is topped with a bracket labeled ns, confirming that the mutation does not significantly impact the kinetics of tension redevelopment in these skeletal muscle fibers. Graph G: Stress-Calcium relationship: The main sigmoid line graph plots Normalized Stress on the vertical axis, ranging from 0.0 to 1.0 in increments of 0.2, against Free C a 2 plus concentration on the horizontal axis, ranging from 0 to 5 micromolar with increments of 1. Both the gray line (W T) and the blue line (Ttn Delta A164-167) show a steep increase in stress between 0.5 micromolar and 2.0 micromolar before plateauing at a normalized stress value of 1.0, indicating that the mutation does not alter the fundamental stress-calcium curve. An inset bar graph quantifies the Ca 2 plus E C 50 values, which represent the calcium concentration required to reach half-maximal stress. The vertical axis for this inset is measured in micromolar from 0.0 to 2.0 with increments of 0.5, and both the gray W T bar and the blue mutant bar plateau at a mean value of approximately 1.1 micromolar. Numerous individual data points are scattered across both bars, and a bracket labeled n s confirms there is no statistically significant difference in calcium sensitivity between the two genotypes. All values are approximate.
Single EDL fiber mechanics. (A) Peak passive stress produced by single skinned EDL fibers across 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 nested ANOVA with Sidak’s multiple comparisons test (represented by asterisks) and exponential growth curve fitting with an extra sum-of-squares F test (P value listed on plot). (D) Maximal active stress produced by single skinned EDL muscle fibers. (E) CSA of EDL fibers used in single-fiber mechanical experiments. (F) Ktr of single skinned EDL fibers. (G) Average stress–calcium relationship of skinned EDL fibers. Statistical significance for D–G inset was determined by nested t test (nested by mouse). Statistical significance for curve fit in G was determined by an extra sum-of-squares F test. For panel A–F experiments, 3 WT and 3 TtnΔA164–167 mice were used, with 3–8 fibers per mouse tested. For panel G, 2 WT and 2 TtnΔA164–167 mice were used, with 5–8 fibers per mouse tested. ns, p ≥ 0.05; **p ≤ 0.01.