Figure 2.

Transient PTP openings cause temporary mitochondrial depolarization (ΔΨ_m) and do not allow calcein permeation. (A) Colocalization of the ΔΨ_m indicator TMRM (red) and mitochondrial Ca²⁺ indicator Fluo-8 (green) in permeabilized cardiac myocytes. Enlarged images are from a portion of the above myocyte at times indicated. (B) Traces were obtained from an individual mitochondrion (or pair), as indicated by white arrows. Depolarization preceded Ca²⁺ loss and gradual repolarization preceded Ca²⁺ refilling. (C) Similar format for simultaneous mitochondrial ΔΨ_m indicator (TMRM) and calcein in a permeabilized cardiac myocyte, with enlarged images showing individual mitochondrion (or pair; arrows) in which depolarization and calcein were simultaneously measured (D). Scale bar=16 μm. The SR Ca²⁺ release protocol (Fig 1) was used.