Influence of electrical stimulation on enzymatic activity of old rat muscles during hindlimb suspension.

1. The purpose of this study was to determine the effects of electrical stimulation on the muscles of older rats (21-24 months old) during suspension hypokinesia/hypodynamia. The rats' hindlimbs were suspended for three weeks, after which the activities of three enzymes were measured in the extensor digitorum longus, the medial gastrocnemius and the soleus muscles. 2. The activity of phosphofructokinase decreased in the soleus muscle and in the white part of the medial gastrocnemius muscle. Malate dehydrogenase and beta-hydroxyacyl-CoA-dehydrogenase showed decreased activity in the red part of the medial gastrocnemius muscle. 3. When electrical stimulation was applied, the activity of the glycolytic enzyme phosphofructokinase increased substantially in all studied muscles. The activity of the malate dehydrogenase and beta-hydroxyacyl-CoA-dehydrogenase enzymes was not influenced by electrical stimulation in the majority of the studied muscles. 4. These results suggest that our electrical stimulation model not only prevents loss of phosphofructokinase activity of aged muscles but increases the activity of anaerobic glycolysis metabolism without affecting the oxidative and fatty acid pathways.