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Effects of Dietary Magnesium on Sodium-Potassium Pump Action in the Heart of Rats¹

Nutrition Research Division, Food Directorate, Health Protection Branch, Health and Welfare Canada, Ottawa, Ontario, Canada K1A 0L2

Sprague-Dawley rats were fed a basal AIN-76 diet containing 80, 200, 350, 500 or 650 mg of magnesium per kilogram of diet for 6 wk. Ventricular slices, as well as microsomal fractions, were prepared from the hearts and were used to determine sodium-potassium pump activity. Sodium-potassium pump activity was assessed in the microsomal membranes by determining the ouabain-inhibitable Na⁺,K⁺-ATPase activity and [³H]ouabain binding, and in the ventricular slices, by determining ouabain-sensitive ⁸⁶Rb uptake under K⁺-free conditions. The ATP-ase activity increased with increasing dietary magnesium, so that in the hearts of those animals that were fed 500 and 650 mg of magnesium/kg diet, it was significantly greater than the activity in the hearts of the animals fed 80 and 200 mg/kg diet. Similarly, ⁸⁶Rb uptake by heart slices from rats fed 500 and 650 mg of magnesium/kg diet was significantly greater than the uptake by heart slices from animals fed 80 and 200 mg/kg diet. [³H]Ouabain binding did not change with increasing dietary magnesium. Thus, magnesium deficiency appears to have no effect on the number of sodium-potassium pump sites, but does decrease the activity of the pump. It is suggested that this leads to an increase in intracellular Na⁺, resulting in a change in the membrane potential, and may contribute to the arrhythmias associated with magnesium deficiency.

KEY WORDS: • magnesium • deficiency • sodium-potassium pump • ATPase • heart

¹ Publication No. 252 of the Bureau of Nutritional Sciences.

Manuscript received 7 April 1987. Revision accepted 24 August 1987.