Thermal activation of F-actin, fast skeletal thin filaments, and cardiac thin filaments on β-cardiac myosin in an in vitro motility assay. (A) Relationship between temperature and the sliding velocity of F-actin (black open squares), skeletal thin filaments (red closed squares), and cardiac thin filaments (blue closed squares) on β-cardiac myosin at pCa 9. Temperature was increased from the baseline of 23°C by IR-laser irradiation for 10 s. n = 545, 354, and 720 for F-actin, skeletal thin filaments, and cardiac thin filaments, respectively. Data expressed as mean ± SEM. (B) Same as in A at pCa 5. n = 931, 1,121, and 872 for F-actin, skeletal thin filaments, and cardiac thin filaments, respectively. (C) Graph comparing the sliding velocity ratios at pCa 9/pCa 5 for F-actin and skeletal thin filament over the range of temperature. Data expressed as mean ± SEM. (D) Arrhenius plot for the sliding velocity of F-actin, skeletal thin filaments, and cardiac thin filaments at pCa 9. T, absolute temperature. Average values from A were used. Sliding velocity (V) is expressed in logarithm. F-actin: V = 5.25 × 1017 exp (−1.00 × 105/RT) (r2 = 0.98). Skeletal thin filaments: V = 1.43 × 1046 exp (−2.72 × 105/RT) (r2 = 0.95). Cardiac thin filaments: V = 2.00 × 1022 exp (−1.30 × 105/RT) (r2 = 0.88). Q10, 3.5, 30, and 5.1 for F-actin, skeletal thin filaments, and cardiac thin filaments, respectively. (E) Same as in D for F-actin, skeletal thin filaments, and cardiac thin filaments at pCa 5. Average values from B were used. F-actin: V = 1.57 × 1016 exp (−9.09 × 104/RT) (r2 = 0.99). Skeletal thin filaments: V = 6.57 × 1013 exp (−7.66 × 104/RT) (r2 = 0.99). Cardiac thin filaments: V = 3.76 × 106 exp (−3.37 × 104/RT) (r2 = 0.89). Q10, 3.1, 2.6, and 1.5 for F-actin, skeletal thin filaments, and cardiac thin filaments, respectively. Data obtained below 32°C (shown in the gray region) were not employed for the fitting in D and E. See Tables S4, S5, and S6 for details.
