An ionic medium induces a loss of mitochondrial Mg2+. The medium contained 0.3 M KCl, 10 mM HEPES, pH 7.20, and 0.1 mM decavanadate (Na+). The mitochondria were spun down at the indicated time after suspension and analyzed for Mg2+. inset, the conditions were the same as panel A except the osmolarity of the medium was kept constant by replacing a portion of the KCl with mannitol. The mitochondria were spun down 4 minutes after suspension for analysis. panel B, the medium contained 0.3 M choline Cl, 10 mM HEPES (TEA+), pH 7.20, and 0.1 mM decavanadate (Na+). 4 μM FCCP, 2 mM ADP (Na+), 1 mM ethanol, and 2 mM EDTA (K+) were present where indicated.