Relation between membrane potential and lactate in gastrocnemius and soleus muscle of the cat during tourniquet ischemia and postischemic reflow

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Abstract
The relation between the lactate content and the membrane potential was investigated in the gastrocnemius and soleus muscle of the cat during and after a 4 h period of ischemia. The skeletal muscle content of ATP and glucose was also measured. No change occurred in the ATP content of the gastrocnemius muscle during the period of ischemia, whereas in the soleus a 40% reduction of ATP occurred. The glucose content decreased during ischemia and increased above initial values after reflow in both muscles. The lactate content increased, and the membrane potential decreased linearly in both muscles during the ischemic period. The final lactate accumulation was higher and the decrease in membrane potential was less in the gastrocnemius than in the soleus. After release of the tourniquet both variables returned to normal or near normal values within 1.5 h in both muscles. A significant correlation was found between the lactate content and the membrane potential in both muscles during the entire experimental period. It is suggested that the depolarisation occurring in skeletal muscle during hypoxia is partly caused by changes in intracellular pH.