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Magnesium ions play a fundamental role in cellular function, but the effects of changes in the concentration of intracellular ionized magnesium (Mg2+i) on cell physiology have only recently received experimental attention. Increasing Mg2+i from 0.3 to 3.0 mM in cardiac cells by internal perfusion has only small effects on the basal voltage-gated calcium current (ICa) or on ICa elevated by dihydropyridine calcium channel agonists. In contrast, ICa elevated by cyclic adenosine monophosphate (cAMP)-dependent phosphorylation decreases by more than 50 percent. The effect of Mg2+i is not due to changes in the concentration of cAMP or in the velocity of phosphorylation but rather appears to be a direct effect on the phosphorylated channel or on channel dephosphorylation.
White et al. (Fri,) studied this question.