Total body potassium, skeletal muscle potassium and magnesium in patients with Bartter's syndrome.

In 20 patients with Bartter's syndrome, who had a serum potassium concentration of 2.75 +/- 0.29 mmol/l (mean +/- SD), the total body potassium (TBK) was measured and compared with a predicted value obtained from regression equations based on age, sex, body height and weight. A significant difference was found between the observed and predicted TBK (mean -320 +/- 306 mmol, p less than 0.01). A positive correlation existed between the serum potassium concentration and the ratio observed TBK/predicted TBK. However, the average fractional reduction in TBK (-11%) was less than the average fractional decrease in serum potassium concentration (-32%). Muscle biopsy specimens were obtained from four patients with Bartter's syndrome and 10 control subjects for analyses of potassium and magnesium. The serum concentrations of potassium and magnesium were decreased in these patients. The potassium content in muscle tissue was lower in two of four patients, but no difference in the amount of magnesium was observed.