Reversible changes of the muscle cell in experimental phosphorus deficiency

Abstract

Either phosphorus depletion or hypophosphatemia may have an adverse effect on muscle function and composition. In chronic alcoholism a variety of toxic and nutritional disturbances could affect the muscle cell, thus obscuring the precise role of phosphorus. Accordingly, 8 conditioned dogs were examinated for the possibility that phosphorus deficiency per se might induce an abnormally low resting transmembrane electrical potential difference (Em) and alter the composition of the muscle fiber. Eight dogs were fed a synthetic phosphorus deficient diet plus aluminium carbonate gel for a 28 day period followed by the same diet with phosphorus supplementation for an additional 28 days. Sequential measurements of Em and muscle composition were made at 0 and 28 days during depletion and again after phosphorus repletion. Serum inorganic phosphorus concentration (mg/100 ml) fell from 4.2±0.6 on day 0 to 1.7±0.1 on day 28. Total muscle phosphorus content (mmol/100 g fat free dry wt [FFDW]) fell from 28.5±1.8 on day 0 to 22.4±2.1 on day 28. During phosphorus depletion, average Em (-mV) fell from 92.6±4.2 to 77.9±4.1 mV (P<0.001). Muscle Na+ and Cl- content (meq/100 g FFDW) rose respectively from 11.8±3.2 to 17.2±2.8 (P<0.01) and from 8.4±1.4 to 12.7±2.0 (P<0.001). Total muscle water content rose from 331±12 to 353±20 g/100 FFDW (P<0.001). A slight, but nevertheless, significant drop in muscle potassium content, 43.7±2.0-39.7±2.2 meq/100 g FFDW (P<0.05) was also noted. After 4 wk of phosphorus repletion, all values had returned to normal. It is concluded that moderate phosphorus depletion can induce reversible changes in skeletal muscle composition and transmembrane potential in the dog, and that it apparently occurs independently of profound hypophosphatemia.