Figure 6.

Myosin heavy chain isoforms in single fibers of the diaphragm from fetal, newborn, and adult sheep. Fibers used in the Ca²⁺, Sr²⁺ activation studies were then treated with solubilizing buffer and proteins separated by SDS-PAGE. Upper panel: identification of MHC isoforms based on molecular weight. Lower panel: Relative density of each MHC isoform, expressed as a percentage of the total density of all MHC protein in the fiber. Data shown as mean ± SEM, where at 70 days gestation [dGA] n = 3 fetuses, 12 fibers; 127 dGA n = 5 fetuses, 20 fibers; term fetuses no breathing [0 min] n = 5 fetuses, 25 fibers; term fetuses + 40 min breathing n = 5 fetuses, 26 fibers; adult, n = 4 ewes, 16 fibers. *P < 0.05, comparison of the same MHC isoform to the previous age or treatment group.