Temperature dependence of the first myosin- and actin-based layer lines. (A and B) Intensity profiles, parallel to the meridional axis, of the myosin- and actin-layer lines (ML1 and AL1), in the range 10°–30°C (color code in the insets) at rest (A) and at the plateau of the isometric tetanus (B), from one muscle. In A, the thin vertical dashed lines represent the limits of integration for the estimate of the temperature dependence of the intensity of ML1 (I_ML1). The thick black dashed line represents the Gaussian intensity distribution expected for AL1 at rest (see text). In B, the thin dashed lines represent the results of the Gaussian fit used to separate the contribution of ML1 (left) and AL1 (right). See text for details. All the profiles shown in A and B are obtained from the same EDL muscle as in Fig. 2 by adding 2 × 20-ms exposures for each state and each temperature. a.u., arbitrary units. (C) Temperature (T) dependence of the intensity of the ML1 layer line at rest (open circles) and at the plateau of the isometric tetanus (black circles), normalized for the value at rest at 30°C. (D) Temperature dependence of the intensity of the AL1 layer line (I_AL1) at the plateau of the isometric tetanus (black circles), normalized for its value at 30°C. The horizontal dashed line represents the expected value of I_AL1 at rest (0.15, see text). Data in C and D are mean ± SEM; six muscles.