Fig. 3: Contractile function in soleus muscles from WT and R2509C mice.

a Typical traces of basal stress after exposure to caffeine. Caffeine at indicated concentrations was applied for 2 min. Soleus muscles from R2509C mice exhibit much greater increase in basal stress after exposure to caffeine than those from WT mice. Pretreatment of muscles with Cpd1 (3 μM) effectively reduces the increase in basal stress caused by caffeine in R2509C muscles. b Dose dependence of the increase in basal stress in response to caffeine exposure. Data are shown as means with individual data points (n = 5 for each group) and were analyzed by one-way ANOVA with Tukey’s test. c Typical traces of basal stress with increased temperature. d The average values of basal stress for 30 s after exposure to 42 °C. Data are shown as means with individual data points (n = 5 for each group) and were analyzed by one-way ANOVA with Tukey’s test. e Typical traces of tension development by electrical stimuli. Muscles were stimulated with 0.5 Hz pulses to evoke twitch and at 1 min intervals with subsequent 20 trains of 1, 2, 5, 10, 20, 50, 100, and 200 Hz pulses. f Summary of twitch tension. Data are shown as means with individual data points (n = 5 for each group) and were analyzed by one-way ANOVA with Tukey’s test. No significant difference was observed between WT and R2509C muscles. Cpd1 (3 μM) significantly reduces twitch tension in both WT and R2509C muscles. g Stress–frequency relationship. Data are shown as means ± SD (n = 5 for each group) and were analyzed by one-way ANOVA with Tukey’s test. No significant difference was observed between WT and R2509C muscles. Cpd1 (3 μM) significantly reduces tetanic stress in both groups. Source data are provided as a Source Data file.