Individual Cardiac Mitochondria Undergo Rare Transient Permeability Transition Pore Openings

RATIONALE:: Mitochondria produce ATP, especially critical for survival of highly aerobic cells such as cardiac myocytes. Conversely, opening of mitochondrial high-conductance and long-lasting permeability transition pores (mPTP) causes respiratory uncoupling, mitochondrial injury and cell death. However, low-conductance and transient mPTP openings (tPTP) might limit mitochondrial Ca load and be cardioprotective, but direct evidence for tPTP in cells is limited. OBJECTIVE:: To directly characterize tPTP occurrence during SR Ca release in adult cardiac myocytes. METHODS AND RESULTS:: Here, we measured tPTP directly as transient drops in mitochondrial [Ca] ([Ca]mito) and membrane potential (ΔΨm) in adult cardiac myocytes during cyclical sarcoplasmic reticulum Ca release, by simultaneous live imaging of 500-1,000 individual mitochondria. The frequency of tPTPs rose at higher [Ca]mito, [Ca]i, with 1 µM peroxide exposure and in myocyte from failing hearts. The tPTPs were suppressed by preventing mitochondrial Ca influx, by mPTP inhibitor cyclosporine A, sanglifehrin and in cyclophilin D knockout mice. These tPTP events were 57 ± 5 s in duration, but were rare (occurring in