REGULATION OF INTRACELLULAR MAGNESIUM IN ASCITES-CELLS - INVOLVEMENT OF DIFFERENT REGULATORY PATHWAYS

Extracellular ATP causes 40% stimulation of Mg2+ efflux from Ehrlich a scites tumor cells (EATC) incubated under O-trans conditions. ATP also causes a threefold increase of arachidonic acid (AA) metabolite relea se from [H-3]AA-preloaded EATC, indicating that, under these experimen tal conditions, it induces phospholipase A(2) (PLA(2)) activation. ATP -induced Mg2+ efflux can be prevented by cyclooxygenase inhibition wit h indomethacin or lysine acetylsalicylate, but not by 5-lipooxygenase inhibition with BWA4C. Mg2+ efflux is also directly stimulated by exog enous AA in a concentration-dependent manner. This phenomenon involves PKA as it is virtually abolished by the specific inhibitor 8-bromoade nosine-3',5'-cyclic monophosphothioate. While stimulating Mg2+ efflux, exogenous AA also increases cAMP content of EATC and this effect can be prevented by cyclooxygenase inhibition. Measurements in mag-fura-a- loaded EATC reveal that stimulation of Mg2+ efflux does not correlate with significant fluctuations of [Mg2+](i). This suggests that Mg2+ ef flux is compensated for by mobilization of bound Mg2+, leaving [Mg2+]( i) unaltered, Altogether these data indicate that Mg2+ efflux can be m odulated by extracellular stimuli capable of activating PLA(2). This m odulation is triggered by cyclooxygenase products which, by activating adenylcyclase, determine an elevation of cAMP. This intracellular mes senger upregulates Na-dependent Mg2+ efflux. (C) 1996 Academic Press, Inc.