Estimation of stability of [³h]-ouabain binding site concentration in rat and human skeletal muscle post mortem

The post mortem stability of the [³H]-ouabain binding site concentration and 3-O-methylfluorescein phosphatase (MFPase) activity was evaluated in rat skeletal muscle. As compared with the values measured in fresh tissue, the [³H]-ouabain binding site concentration in rat soleus muscle only dropped by around 1 % per hour post mortem and a significant decrease was only seen after 12 h (15% p < 0.02). The 3-O-MFPase activity in rat gastrocnemius muscle showed a similar decrease. After 4 days, both parameters had dropped by 65% (p < 0.001). In contrast, when intact fresh rat soleus muscles were incubated in Krebs-Ringer bicarbonate buffer at 20 d̀C for 4 days no significant decrease was seen in the [³H]-ouabain binding site concentration. In 10 human subjects the concentration of [³H]-ouabain binding sites was measured in specimens of the vastus lateralis muscle obtained within half an hour and at 6 and 12 h post mortem. The relative decrease after 6 h was insignificant (8% p<0.30), whereas it was significant after 12 h (29% p<0.005). These results have shown that the [³H]-ouabain binding sites in human skeletal muscle are resistant to post mortem degradation during the first 6 h after death. This makes it possible to perform measurements post mortem of the [³H]-ouabain binding site concentration in human skeletal muscle.