Temporal alterations of intracellular Na,K, Ca,Mg, and PO4 in muscle beneath the burn wound

Three days after a single hindlimb scald in the rat, soleus muscle from the burned limb, but not from the contralateral unburned limb, shows an elevation in glucose uptake and utilization, an increase in protein turnover, and a loss of responsiveness to insulin. To assess the relationship of extra- and intracellular electrolyte concentrations to the changes, rats were scalded on one hindlimb and compared to controls at 4 hr, 1 day, and 3 days postburn. There were no pronounced changes in serum sodium, potassium, or calcium levels of burned rats. Serum concentrations of magnesium and phosphate, however, were elevated 4 hr postburn but were significantly lower than controls 3 days later. Intracellular electrolytes in soleus muscles from the unburned limb of burned rats were comparable to those in control muscles. In contrast, thermal injury resulted in profound intracellular electrolyte alterations in soleus muscles from the burned limb. Four hours postburn, the intracellular sodium concentration was elevated 210% (P < 0.001) whereas the concentrations of potassium, magnesium, and phosphate were reduced 44, 24, and 41% (P < 0.001), respectively. In the ensuing 3 days, all four ions returned to, or closely approached, the intracellular concentrations in control muscles. Unlike these transient alterations, thermal injury led in burned limb muscles to a progressive accumulation of cellular calcium reaching values 18-fold higher (P < 0.001) than control values 3 days postburn. The data suggest that this increase in cellular calcium could be linked to the chronic increase in glucose metabolism and protein turnover which develop in thermally injured muscle.