Fig. 4.

Increased sarcomere lattice spacing and disorganized myosin movement in C2^−/− EDL intact muscles and skinned fibers. (A, Left) X-ray diffraction pattern of EDL muscle at rest (Right) and during contraction. Equatorial reflections (I₁₁ and I₁₀) and layer line patterns (MLL4, ALL6, and ALL7) are as indicated. (B) Force as a function of time during maximally activated isometric tetanus of EDL muscle. X-ray exposures (10 ms) were taken every 20 ms during isometric contraction. (C) Linear relationship of the ratio of I₁₁ to I₁₀ (I₁₁/I₁₀) to force development. Slope of I₁₁/I₁₀, as a function of force, is steeper in C2^−/−. (D) Average I₁₁/I₁₀ during rest and maximal contraction. X-axis indicates resting (1 and 2) and plateau periods during the contraction as shown in Fig. 4B. (E) Change in I₁₁/I₁₀ relative to rest during isometric muscle contraction. (F) Calculated lattice spacings in intact EDL muscle at optimal muscle length (L_o) (G) and skinned EDL fibers at sarcomere length 2.2 µm. (H) Intensity of MLL4 in resting EDL muscle (n = 6 to 9 in each group). Error bars represent ± SEM, *P < 0.05 and **P < 0.01. Statistical analyses were performed in all groups by unpaired t test or ordinary two-way ANOVA followed by Bonferroni’s multiple comparison test.