Regulation of intracellular Mg2+ by superoxide in amnion cells.

Changes of intracellular free Mg2+ concentration (Mg2+]i) in human amnion cells induced by superoxide anion were determined using a highly Mg(2+)-sensitive fluorescent dye Mg(2+)-fura2 or Mg(2+)-indol. Superoxide anion, produced by addition of xanthine oxidase to hypoxanthine, induced decrease of Mg2+]i. The decrease was significantly inhibited by an anion channel blocker, 4,4'diisothiocyano-2,2' disulfonic acid stilbene (DIDS). Superoxide dismutase (SOD), injected into cells by cell fusion, also inhibited the change of Mg2+]i, but catalase did not. Superoxide anion induced prompt increase of intracellular pH (pHi) as well as decrease of Mg2+]i and subsequently activated the increase of intracellular free Ca2+ (Ca2+]i) and the release of arachidonate. In contrast to superoxide anion, NH4Cl which induces increase of pHi in amnion cells increased Mg2+]i. The elevation of basal level of Mg2+]i by Mg(2+)-ionophore inhibited the change of Ca2+]i and the release of arachidonate induced by superoxide anion. These results suggest that superoxide anion, transported through anion channels into cells, decreases Mg2+]i directly, not due to a pH-effect and that the decrease of Mg2+]i may regulate biological functions of the cells via increase of Ca2+]i.