Impaired mineral metabolism in postburn muscle

Rats were scalded on one hind limb and sacrificed by exsanguination at 4 hours, 1 day, and 3 days postburn. Concentrations of sodium, potassium, calcium, magnesium, and phosphate were measured in serum and in calf muscles from the burned and unburned limb of burned rats and controls. At 4 hours postburn, the injured rats exhibited a 5.4% elevation in serum potassium, a 23% increase in serum magnesium, and a 15% rise in serum phosphate compared to controls. At 3 days postburn, serum calcium and phosphate levels of burned rats were 7 and 13%, respectively, below controls. Tissue electrolytes in calf muscles from the unburned limb of burned rats did not differ from controls. In contrast, calf muscles of the burned limb showed up to a 202% increase in sodium content and up to a 61% fall of potassium content; the tissue Na/K ratio was elevated more than threefold at all test times. Burned muscles' calcium content was increased 127% at 4 hours, 112% at 1 day, and 21% at 3 days postburn. Magnesium and phosphate contents did not differ from controls at 4 hours postburn, but gradually decreased 58 and 59%, respectively, during the observation period. The data suggest that muscles underlying the burned wound show increased cell permeability and/or impaired active ion transport. These alterations as well as the loss of magnesium and phosphate may be related, in part, to the previously demonstrated depletion of ATP and adenine nucleotides in thermally injured muscles.