CHARACTERIZATION OF MAGNESIUM EFFLUX FROM EHRLICH ASCITES TUMOR-CELLS

Magnesium efflux from intact Ehrlich ascites tumor cells (EATC) has be en characterized under 0-trans conditions. It is shown that a magnesiu m-extruding mechanism operates in these cells which brings about magne sium efflux up to 20% of the cell total content. EATC magnesium efflux is independent from extracellular Ca2+ and its apparent velocity is n ot affected by [Mg2+], up to 160 mu M. This extrusion, however, is str ictly dependent on extracellular Na+ and it is inhibited by ouabain (1 mM), amiloride (1 mM), imipramine (0.5 mM) and quinidine (1 mM). It i s not affected by HMA (5-(N,N-hexamethylene) amiloride) (0.5 mu M) and vanadate (0.1 mM). Bumetanide (0.5 mM) enhances magnesium extrusion i n these cells. EATC magnesium extrusion can be significantly stimulate d by db cAMP, forskolin, and IBX (3-isobutyl- 1-methyl-xanthine). The intracellular magnesium distribution, studied also by means of the ion ophore A23187, is regulated by energy metabolism and cell ATP content. Altogether our data demonstrate that EATC exhibit a magnesium extrusi on sustained by Na+ gradient across the plasma membrane and carried ou t by a Na+/ Mg2+ antiport. In these cells magnesium homoeostasis resul ts, regulated efficiently by cell ATP and cAMP content. (C) 1994 Acade mic Press, Inc.