Figure 1.

Mitochondrial membrane potential oscillations in myocytes of the intact heart perfused with Ca²⁺-free buffer. a, b) The ΔΨ_m signal (TMRE fluorescence) was stable over many minutes in hearts perfused with modified Tyrode’s containing 0.5 mM Ca²⁺ even after a localized laser flash was applied (white arrowhead in panel a, arrow in panel b). c, d) After 2–3 min of normoxic perfusion with Ca²⁺-free Tyrode’s, ΔΨ_m became unstable and spontaneous oscillations were observed. Sustained oscillations in ΔΨ_m were observed for several minutes in the cell indicated by the yellow dashed line in panel c. Both intracellular and intercellular heterogeneity of ΔΨ_m is evident in the epicardial optical sections. Scale bars in a and b equal 20 microns.