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Muscle Changes in Rats Fed Magnesium and Calcium Deficient Diets¹

West Virginia University, Morgantown, West Virginia 26506

The effects of diets deficient in magnesium and/or calcium on muscle function were examined in rats. During a 2-week period, rats weighing between 200 and 225 g were fed one of four diets: control (78 mg Mg/100 g diet, 740 mg Ca/100 g diet), magnesium-deficient (0.3 mg Mg/100 g diet, 740 mg Ca/100 g diet), calcium-deficient (78 mg Mg/100 g diet, 2 mg Ca/100 g diet) or magnesium- and calcium-deficient (0.3 mg Mg/100 g diet, 2 mg Ca/100 g diet). After 14 days the magnesium-deficient rats exhibited erythema and increased irritability and were judged hypomagnesemic. When rats were fed a diet deficient in only magnesium, resulting in a serum magnesium concentration of less than half the serum magnesium concentration of the control group, muscle Mg-ATPase activity was lower and muscle and urinary taurine concentrations were higher than the respective concentrations of the control group. Resting membrane potentials from the soleus muscle were lower than potentials from control muscle, and serum alkaline phosphatase activity was lower than the serum activities from all other diets. The data for the ⁴⁵Ca binding assay indicated the effect of a magnesium-deficient diet was not the same when calcium was adequate or deficient. When rats were fed a diet deficient only in calcium, the serum magnesium increased and the urinary taurine concentrations decreased. When rats were fed diets deficient in both magnesium and calcium, urinary magnesium and taurine concentrations decreased and the resting membrane potentials were lower than the control muscle membrane potentials. The effect of magnesium-deficiency in the rat appears to be membrane-oriented as evidenced by changes in resting membrane potentials, serum ion concentration changes, increased muscle and urinary taurine concentrations, changes in ⁴⁵Ca binding and decreased Mg-ATPase activity.

KEY WORDS: • hypomagnesemic • taurine • membrane potential • sacroplasmic reticulum (SR)

¹ Published with the approval of the director of the West Virginia Agricultural and Forestry Experiment Station as Scientific Paper No. 1552. The authors gratefully acknowledge Dr. Robert S. Dunbar, Jr. for valuable assistance in the statistical analysis.

Manuscript received 10 July 1978.