Comparison of magnesium and potassium efflux from incubated rat diaphragms

Intracellular magnesium has been shown to be less available for prompt isotopic exchange than intracellular potassium in the intact mammal. Therefore, an experiment was completed to establish if magnesium would leave a tissue as readily as potassium under conditions known to cause a loss of the latter ion. Rat diaphragms were incubated at 37° and 3°C. After a 4-hour incubation at 3° it was observed that the potassium loss was greater than 50% of the initial tissue concentration, and the loss of magnesium was less than 20% of the initial concentration. These studies indicate that intracellular magnesium is restricted in a way different from that of potassium. The muscle loss of potassium and retention of magnesium at 3°, when metabolic processes were greatly reduced, are consistent with the concept of greater lability of intracellular potassium as revealed by isotope studies and with the concept of the dependence of intracellular potassium concentrations on metabolic activity in distinct contrast to intracellular magnesium.