Na(+)-dependent Mg2+ efflux from Mg(2+)-loaded rat thymocytes and HL 60 cells.

Mg(2+)-loaded rat thymocytes and HL 60 (human promyelocytic leukemia) cells expressed a high rate of Na(+)-dependent net Mg2+ efflux which was inhibited by two thirds by 1 mM amiloride. During net Mg2+ efflux, extracellular Na+ was taken up at a stoichiometric ratio of 2 Na+ to 1 Mg2+, indicating electroneutral Na+/Mg2+ antiport as found for erythrocytes. Na(+)-independent Mg2+ efflux was not significantly expressed in these cell types.