Fig. 7. Single fiber mechanics in type IIB fibers (EDL muscle) of Compound-Het mice.
a Top: MHC-gel. Examples of IIB single fibers that were used in experiment. Two Compound-Het and two WT fibers are shown and a total of 41 WT and 40 Compound-Het fibers were studied; (WT: 34/41 fibers were IIB; Compound-Het: 28/40 fibers were IIB). The left lane is a standard with all MHC isoforms. a Bottom: Specific force –pCa relations of Compound-Het and WT fibers. A Hill-type curve-fit analysis shows that the Compound-Het fibers are significantly different from WT fibers. b Maximal specific force is reduced in Compound-Het fibers (p = 0.046). c The force/stiffness relation is unaltered. Increase in calcium sensitivity (p = 0.028) (d) but unchanged cooperativity (e) in Compound-Het fibers. (Values based on force-pCa curves that were normalized to the maximal specific force.) Kinetics of tension redevelopment as reflected in ktr (f) and maximal shortening velocity (g) are unaltered in Compound-Het fibers. The data set comprises on average 7 type IIB fibers from each of 5 WT mice and 5 type IIB fibers from each of 6 Compound-HET mice. Values are mean ± SEM. a: allosteric sigmoidal non-linear least squares fit with as null hypothesis that one curve fits all data sets. Test (Sum-of-squares F-test) reveals that the null hypothesis is rejected (p ≤ 0.0001, F (DFn, DFd) 8.146 (3,360)). b–g two-tailed unpaired t-test. *p < 0.05; ****p < 0.0001. Source data are provided as a Source Data file.