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 Ca2+ load and be cardioprotective, but direct evidence for tPTP in cells is limited.
Objective: To directly characterize tPTP occurrence during SR Ca2+ release in adult cardiac myocytes.
Methods and Results: Here, we measured tPTP directly as transient drops in mitochondrial [Ca2+] ([Ca2+]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 [Ca2+]mito, [Ca2+]i, with 1 µM peroxide exposure and in myocyte from failing hearts. The tPTPs were suppressed by preventing mitochondrial Ca2+ 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 <0.1% of myocyte mitochondria at any moment) such that the overall energetic cost to the cell is minimal. The tPTP pore size is much smaller than for permanent mPTP, as neither Rhod-2 nor calcien (600 Da) were lost. Thus, proteins and even molecules the size of NADH (663 Da) will be retained during these tPTP.
Conclusions: We conclude that tPTP openings (MitoWinks) may be molecularly related to pathological mPTP, but are likely to be normal physiological manifestation that benefits mitochondrial (and cell) survival by allowing individual mitochondria to reset themselves with little overall energetic cost.
- Received November 30, 2015.
- Revision received December 21, 2015.
- Accepted December 28, 2015.