Regulation of intracellular magnesium in ascites cells: involvement of different regulatory pathways.

Abstract Extracellular ATP causes 40% stimulation of Mg 2+ efflux from Ehrlich ascites tumor cells (EATC) incubated under 0-trans conditions. ATP also causes a threefold increase of arachidonic acid (AA) metabolite release from [ 3 H]AA-preloaded EATC, indicating that, under these experimental conditions, it induces phospholipase A 2 (PLA 2 ) activation. ATP-induced Mg 2+ efflux can be prevented by cyclooxygenase inhibition with indomethacin or lysine acetylsalicylate, but not by 5-lipooxygenase inhibition with BWA4C. Mg 2+ efflux is also directly stimulated by exogenous AA in a concentration-dependent manner. This phenomenon involves PKA as it is virtually abolished by the specific inhibitor 8-bromoadenosine-3′,5′-cyclic monophosphothioate. While stimulating Mg 2+ efflux, exogenous AA also increases cAMP content of EATC and this effect can be prevented by cyclooxygenase inhibition. Measurements in mag-fura-2-loaded EATC reveal that stimulation of Mg 2+ efflux does not correlate with significant fluctuations of [Mg 2+ ] i . This suggests that Mg 2+ efflux is compensated for by mobilization of bound Mg 2+ , leaving [Mg 2+ ] i unaltered. Altogether these data indicate that Mg 2+ efflux can be modulated by extracellular stimuli capable of activating PLA 2 . This modulation is triggered by cyclooxygenase products which, by activating adenylcyclase, determine an elevation of cAMP. This intracellular messenger upregulates Na-dependent Mg 2+ efflux.