Stereologic analysis of normal and dystrophic avian αW myofibers

Abstract

The αW fibers of the posterior latissimus dorsi from normal (NPLD) and dystrophic (DPLD) chicks were analyzed by stereologic methods for electron microscopy. The αW fibers were located in electron micrographs by comparison with adjacent frozen sections where αW fibers were identified by established histochemical criteria. Striking mitochondrial and sarcotubular alterations were detected in dystrophic αW fibers prior to involvement of myofibrils. These changes are interpreted as features of an incipient stage of dystrophy that occur in αW fibers before degenerative changes. The volume fraction of myofibrils from αW fibers of the DPLD was 5% less than that of the NPLD. The volume densities of mitochondria were similar for both types of muscle. Mitochondrial surface density was 30.5% higher in DPLD than in NPLD. The surface-to-volume ratio of mitochondria was also 30.5% higher in DPLD than in NPLD. In DPLD, both surface density and volume density of terminal cisterns were 44% more than in NPLD. Volume density of the longitudinal tubules declined 18%, from 3.58 ± 0.13% in NPLD to 2.93 ± 0.20% in DPLD. The smaller decline in surface density of the longitudinal tubules in the DPLD plus a 14% increase in surface-to-volume ratio indicates that they are fewer in number and narrower in diameter than in the NPLD. Volume density of the transverse tubules was 188% greater and their surface density 162% greater in DPLD than in NPLD.