Muscle electrolytes and fluid compartments in six children with Bartter's syndrome.

1. Muscle electrolyte (Na, K, Cl, P) concentra­ tions and fluid compartments of six children with Bartter's syndrome were compared with those of 17 control children. From four of the patients biopsies were taken twice, before and after treat­ ment with potassium chloride and spironolactone. Muscle electrolytes were determined by neutron activation in tissue sampled by needle biopsy. Results were expressed in relation to fat-free dry solids. Trapped extracellular fluid was calculated from the chloride space, a normal resting mem­ brane potential being assumed. 2. In hypokalaemic patients total muscle potassium (Km) (33-0 ±2-1 SEM) was below the normal range (43-8 + 0-7 mmol/100 g of fat-free dry solids) in all cases. When plasma potassium was corrected, total muscle potassium returned to normal. There was a significant correlation between plasma potassium concentration and total muscle potassium (r = 0-87; P<0^01). Total muscle sodium (Nam) was increased: 18-7 + 2-9 mmol/100 g in hypokalaemic patients (11·3 ± 0-6 mmol/100 g of fat-free dry solids in control subjects). A negative relationship was found between Km and Nam (r = -0-85; P < 0-01). With treatment, intracellular potassium concentration remained low (142-0 mmol/1 of intracellular water; control, 163-0 ±2-4 mmol/1) despite normokalaemia and normal total muscle potassium. Muscle phosphorus (32-1 ± 1-8 mmol/100 g) was higher than in control subjects (28-1 + 0-4 mmol/100 g of fat-free dry solids).