Regulation of Na+/Mg2+ antiport in rat erythrocytes

In rat erythrocytes, the regulation of Na+/Mg2+ antiport by protein kinases (PKs), protein phosphatases (PPs), intracellular Mg2+, ATP and Cl- was investigated. In untreated erythrocytes, Na+/Mg2+ antiport was slightly inhibited by the PK inhibitor staurosporine, slightly stimulated by the PP inhibitor calyculin A and strongly stimulated by vanadate. PMA stimulated Na+/Mg2+ antiport. This effect was completely inhibited by staurosporine and partially inhibited by the PKC inhibitors Ro-31-8425 and BIM I. Participation of other PKs such as PKA, the MAPK cascade, PTK, CK 1, CK 11, CAM II-K, PI 3-K, and MLCK was excluded by use of inhibitors. Na+/Mg2+ antiport in rat erythrocytes can thus be stimulated by PKCalpha. In non-Mg2+-loaded erythrocytes, ATP depletion reduced Mg2+ efflux and PMA stimulation in NaCl medium. A drastic activation of Na+/Mg2+ antiport was induced by Mg2+ loading which was not further stimulated by PMA. Staurosporine, Ro-31-8425, BIM I and calyculin A did not inhibit Na+/Mg2+ antiport of Mg2+-loaded cells. Obviously, at high [Mg2+](i) Na+/Mg2+ antiport is maximally stimulated. PKC, or PPs are not involved in stimulation by intracellular Mg2+. ATP depletion of Mg2+-loaded erythrocytes reduced Mg2+ efflux. and the affinity of Mg2+ binding sites of the Na+/Mg2+ antiporter to Mg2+. In non-Mg2+-loaded erythrocytes Na+/Mg2+ antiport essentially depends on Cl-. Mg2+-loaded erythrocytes were less sensitive to the activation of Na+/Mg2+ antiport by [Cl-](i). (C) 2004 Elsevier B.V All rights reserved.,