POST-MORTEM CHANGES IN SUBCELLULAR FRACTIONS FROM NORMAL AND PALE SOFT EXUDATIVE PORCINE MUSCLE .1. CALCIUM ACCUMULATION AND ADENOSINE TRIPHOSPHATASE ACTIVITIES

SUMMARY– Myofibrillar, mitochondrial, heavy sarcoplasmic reticulum and light sarcoplasmic reticulum fractions were isolated by differential centrifugation of homogenates from normal and pale, soft, exudative (PSE) porcine muscle at various times post‐mortem. Calcium uptake was measured using a solution containing45Ca++. The oxalate‐stimulated calcium accumulating ability of the subcellular fractions declined 5‐10 fold between 0 and 24 hr post‐mortem. The major portion of this decline occurred in the first hour after death in fractions from PSE muscle but was more gradual in the normal fractions. The ATPase activities of normal and PSE fractions obtained at death did not differ significantly. These activities increased with time post‐mortem in most normal fractions but decreased in those from PSE muscle. The subcellular site of ATP hydrolysis post‐mortem was discussed. The results obtained point to the potential importance of the relaxing, factor in muscle post‐mortem. Copyright © 1969, Wiley Blackwell. All rights reserved