Fig. 2.

Decreased whole-muscle function, single-cell function, and myofilament structure in Clock^Δ19, Bmal^−/−, and MyoD^−/− mice. (A) Representative force trace from the measurement of specific tension of whole-muscle (EDL) from wild-type mice. (B) Histogram of the average specific tensions of muscles for Clock^Δ19, Bmal1^−/−, and MyoD^−/− mice (n = 3–6/strain). Significant difference (P < 0.05) from wild type is denoted by an asterisk. (C) Results from single-fiber mechanical analyses of wild-type (△) and Bmal1^−/− (○) muscle fibers. Each point on the curve represents the average ± SEM for measures of 7–20 cells at each calcium concentration. (D) Data from C reported as tension relative to maximal tension for each calcium concentration. (E) Representative myofilament images obtained by electron microscopy (43,000×) from wild-type, Clock^Δ19, Bmal1^−/−, and MyoD^−/− gastrocnemius muscles. The normal organization of thin and thick filaments is disrupted in muscle from the three different mutant animals.