Post-mortem degradation of gap filaments at different post-mortem pHs and temperatures

Super-stretched muscle fiber bundles (<10 min post mortem) were incubated at one of four combinations of temperature and pH (pH 5.5, 37°C; pH 5.5, 0-4°C; pH 7.4, 37°C; pH 7.4, 0-4°C) for 1 h prior to fixation and embedding for transmission electron microscopy. These tissues were compared with controls fixed immediately after stretching. Disruption of gap filament ultrastructure was greatest in those muscle bundles incubated at pH 5.5 and 37°C. It was determined that pH had a greater influence upon gap filaments than did temperature and that pH 5.5 caused more gap filament disruption than pH 7.4. Other structural alterations of the stretched muscle included more glycogen granule disruption at pH 7.4 and pulling of groups of thick filaments toward the Z-lines within a sarcomere. A pulling of alternate thick filaments toward opposite Z-lines was not observed. It was concluded that gap filament disruption may occur very rapidly in post-mortem muscle.