The resting membrane potential difference (Em) of skeletal muscle was measured in 26 normal human subjects, 7 patients with mild illness, and 21 patients with severe, debilitating medical disorders. A closed transcutaneous approach to the muscle was made by needle puncture and the Em was measured utilizing standard Ling electrodes. Measurements revealed an Em of -88 +/-3.8 mv in healthy subjects and -89 +/-2.1 mv in patients hospitalized for minor medical problems. The mean Em in 21 in-hospital patients, judged to be severely ill clinically from a variety of causes, was -66.3 +/-9.0 mv. Open deltoid muscle biopsies were performed in 7 of the healthy subjects and in 13 of the severely ill group. Estimation of the intra-extracellular water partition was made by calculating the chloride space from the previously measured Em. Analysis of the muscle samples revealed no significant difference in the intra-extracellular potassium ratios of the two groups biopsied. Intracellular Na(+) concentrations were uniformly increased in the muscle samples of the severely ill subjects and averaged 42.3% higher than those of the normal subjects. The mechanisms which might account for the elevation of intracellular Na(+) and a depression of Em independent of changes in intra-extracellular K(+) ratios are discussed and it is suggested that this defect may be a generalized cellular abnormality which is a common quality of serious illnesses.
