Electron microscopy of postmortem autolysis of rat muscle tissue.

To define the progression of ultrastructural changes in normal muscle at post mortem, rat gastrocnemius muscles were studied at various times after storage at +4 degrees C and +22 degrees C. Degeneration of the I-zone (discoid necrosis) and membranous bodies were found to be similar to that seen in muscle diseases, and lamellar formations were seen in mitochondria. At +4 degrees C there was contraction of the sarcomere which vanished in 12 h and inter-filamentous oedema appeared. Z-line degeneration was seen at 24 h and at 4 days all Z-lines had disappeared, and the H-zone showed darkening. In the same samples collapse or ruptures of the I band were seen. At 8 days the H-zones and M-lines were still discernible. In the early stages the mitochondria showed swelling and loss of matrix granules, while later they showed broken cristae and outer membranes, and flocculent densities. At 4 days rearrangement of the cristal material into long pentalaminar "needles" was seen in a few mitochondria. At 4 and 8 days membranous bodies were seen and the T-system and sarcoplasmic reticulum showed ruptures and disintegration into vesicles. The nucleus showed increasing condensation of chromatin at the periphery and clearing of the center. Polysomes and glycogen were reduced at 2 h, and has practically vanished at 24 h. At 22 degrees C the changes were the same but appeared about 4 times as quickly as at +4 degrees C.