Brain‐derived respiring mitochondria exhibit homogeneous, complete and cyclosporin‐sensitive permeability transition

Abstract

The mitochondrial permeability transition (mPT) is increasingly implicated in neuronal cell death. In the present study, isolated respiring brain mitochondria were examined for their ability to undergo calcium-induced mPT and their sensitivity to mPT inhibition by cyclosporin A (CsA). Previous studies have suggested a heterogeneous response to calcium, a limitation of CsA inhibition, and a relative resistance in the ability of respiring brain mitochondria to undergo mPT. Using fluorometric and electron microscopic analyses, we found that virtually the whole population of respiring brain mitochondria readily undergo mPT and swell upon calcium exposure. Further, brain mitochondria were highly sensitive to CsA which potentiated morphological recovery after transient swelling as well as completely blocked mPT induction in the presence of a low concentration of ADP. Using flow cytometry, which allows analysis of individual mitochondria, we demonstrate that both brain and liver mitochondria display homogeneous responses to calcium-induced mPT. We conclude that the mPT is one likely target for the broad in vivo neuroprotective effects displayed by CsA when allowed to penetrate the blood-brain barrier, and that development of compounds inhibiting mPT may prove beneficial for the treatment of severe brain disease.

Kinetic Model for Ca2+-induced Permeability Transition in Energized Liver Mitochondria Discriminates between Inhibitor Mechanisms

“…A decrease in light scattering has been shown to correlate with the percentage of mitochondria undergoing swelling as a result of mPT (28). Our results are in agreement with earlier publications showing the correlation measured using a conventional fluorescence spectrometer (29).…”

Multifunctional Drugs for Head Injury

“…171 This effect was dose-dependent and was correlated to an improvement in brain oxygen consumption after trauma. The preserved brain oxygen consumption after TBI was thought to reflect improved mitochondrial function, which is consistent with the ability of CyA to inhibit the mitochondrial permeability transition, 19,172,173 and in so doing, prevent mitochondrial swelling and improve energy recovery. 174 Such effects would also inhibit calcium accumulation, apoptosis and block free radical production.…”

“…17 Following injury, this organelle has been shown to undergo a mitochondrial permeability transition, 18 with the permeabilization of the inner mitochondrial membrane being associated with excessive calcium accumulation. 19,20 Mitochondrial permeability transition results in the release of cytochrome c, which is integrally involved in apoptotic cell death, as well as in uncoupling and inhibition of oxidative phosphorylation and the generation of mitochondrial reactive oxygen species (ROS). 20,21 This propensity of mitochondria to undergo permeability transition has also been implicated in the selective vulnerability of different brain regions to an ischemic insult.…”

Binding mitochondria to cryogel monoliths allows detection of proteins specifically released following permeability transition

“…The objective of the present study was to establish a method, which would allow detection of proteins released specifically from mitochondria following stimulation with agents known to promote mitochondria permeabilisation. To achieve this, mitochondria were attached to monoliths, unspecific proteins were washed away, and mitochondria were subjected to calcium or a combination of Bid and Bax in doses that resulted in large amplitude swelling in mitochondria in suspension [9]. We demonstrate that proteins specifically released from mitochondria can be isolated and identified without the problem of a high background of unspecifically released proteins.…”

“…The principal activator of the mPTP is calcium; the concentration required depends on the surrounding conditions. Mitochondrial permeability transition (mPT) can be induced by increased calcium concentration in vivo [6,7] as well as in vitro [8][9][10][11] and may be reversed by removing calcium [9] or prevented by the administration of inhibitors of mPTP, such as cyclosporin A or its non-immunosuppressive analogues [12]. In the experimental setting, membrane permeabilisation can be achieved by drugs such as the mPTP inducer atractyloside or the ionophore alamethicin.…”