Individual Cardiac Mitochondria Undergo Rare Transient Permeability Transition Pore Openings

Abstract

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.

Mitochondrial Ca2+ and regulation of the permeability transition pore

“…Interestingly, these transient openings operate at a subconductance state and appear to allow solutes no larger than 300–600 Daltons to pass. The different modes of opening could provide a means for selective signaling and indicate that transient openings could be a result from lower oligomerization configurations of the pore (Ichas et al 1997; Lu et al 2015). …”

Sex differences in the regulation of spatially distinct cardiac mitochondrial subpopulations

“…The molecular composition of the MPTP is not established and still a matter of debate. Recently, literature has shown that few components are essential for MPTP formation such as F O F 1 ATP synthase dimmers and cyclophilin D and a transient mode has also been proposed [53]. But the unsolved question is how sex hormones affect MPTP formation?…”

New and revisited approaches to preserving the reperfused myocardium

“…As calcium and ROS are postulated to increase the probability of the opening of the PTP, strategies that reduce ROS and lower mitochondrial calcium overload have been extensively explored as cardioprotective interventions 25,27 . Paradoxically, transient PTP opening seems to reduce mitochondrial calcium overload, analogous to a ‘pressure release valve’, whereby mitochondrial calcium decreases upon transient PTP opening 112 . This mechanism works to reset mitochondrial calcium concentration, and is postulated to prevent the sustained, large conductance, open conformation of PTP that is associated with pathological injury and cell death.…”