Efflux of magnesium and potassium ions from liver mitochondria induced by inorganic phosphate and by diamide.
Addition to rat liver mitochondria of 2 mM inorganic phosphate or 0.15 mM diamide, a thiol-oxidizing agent, induced an efflux of endogenous Mg2+ linear with time and dependent on coupled respiration. No net Ca2+ release occurred under these conditions, while a concomitant release of K+ was observed. Mg2+ efflux mediated either by Pi or low concentration of diamide was completely prevented by EGTA, Ruthenium red, and NEM. These reagents also inhibited the increased rate of state 4 respiration induced both by Pi and diamide. At higher concentrations (0.4 mM), diamide induced an efflux of Mg2+ which was associated also with a release of endogenous Ca2+. Under these conditions EGTA completely prevented Mg2+ and K+ effluxes, while they were only partially inhibited by Ruthenium red and NEM. It is assumed that Mg2+ efflux, occurring at low diamide concentrations or in the presence of phosphate, is dependent on a cyclic in-and-out movement of Ca2+ across the inner mitochondrial membrane, in which the passive efflux is compensated by a continuous energy linked reuptake. This explains the dependence of Mg2+ efflux on coupled respiration, as well as the increased rate of state 4 respiration. The dependence of Mg2+ efflux on phosphate transport is explained by the phosphate requirement for Ca2+ movement.
D000818:Animals; D001391:Azo Compounds / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D003958:Diamide / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D010710:Phosphates / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D051381:Rats; D012430:Ruthenium Red / Q000494:pharmacology
D001391:Azo Compounds; D010710:Phosphates; D003958:Diamide; D012430:Ruthenium Red; D004533:Egtazic Acid; D008274:Magnesium; D005033:Ethylmaleimide; D011188:Potassium; D002118:Calcium