Transient induction of the mitochondrial permeability transition by uncoupler plus a Ca(2+)-specific chelator.

Determinations of aqueous space volumes, swelling and Mg2+ release experiments demonstrate that EGTA plus uncoupler causes the permeability transition in Ca(2+)-loaded mitochondria. Extramitochondrial Mg2+ is required to obtain this effect. Changes in transition-dependent parameters are smaller and more varied when induced by EGTA plus uncoupler than when induced by Ruthenium red plus uncoupler, although inhibitor-sensitive experiments show that the same basic mechanism is involved in both cases. Measurements of sucrose trapping and sucrose or inulin accessible space, after changes in transition-dependent parameters are complete, indicate that rapid reversal occurs when the transition is induced by EGTA plus uncoupler, explaining why limited responses are obtained. Data support the hypothesis that an external divalent cation binding site regulates activity of the mitochondrial Ca2+ uniporter.