Mitochondrial Physiology Network 10.9: 72 (2005) - download pdf

The permeabilisation of mitochondria and bilayer phospholipid membranes by palmitic acid and Ca²⁺.

Nils-Erik L Saris,¹ K Beloslutdsev,² E Gritsenko,² A Agafonov,² M Ovize,³ N Beloslutdseva,² O Gateau-Roesch,³ GD Mironova²

¹Dept. Applied Chemistry Microbiology, POB 56 Biocenter 1, FIN-00014 University Helsinki, Finland; ²Inst. Theoretical Experimental Biophysics, Russian Academy Sciences, Pushchino, Moscow Region, Russia; ³INSERM E 0226, Faculté de médecine Lyon Nord, Université Claude Bernard Lyon1, Lyon, France. - nils-erik.saris@helsinki.fi

    Palmitic acid (PAL) has recently been found to be a physiological activator of apoptosis [1]. PAL induced the opening of a cyclosporin A (CsA)- insensitive pore in mitochondria [2]. In  the present study we compared the properties of this pore with the well-known CsA-sensitive mitochondrial permeability transition pore (PTP). Also the contribution of the PAL/Ca²⁺-activated pore in the release of cytochrome c from mitochondria was studied.

    We found that the PAL/Ca²⁺-induced CsA-insensitive swelling of mitochondria was not affected by the ADP - an inhibitor of PTP opening - nor by openers of this pore (inorganic phosphate, atractyloside). However, this swelling was inhibited by physiological concentration ATP ([I]₅₀ = 1.3 mM), which is a less effective inhibitor of PTP. This action of ATP occurs from the outside of the inner mitochondrial membrane. Earlier we found that PAL bound Ca²⁺ with high affinity [3]. Palmitoleic acid and 2-bromopalmitic acid, which have no such high Ca²⁺ affinity, failed to induce the pore opening. These results are in agreement with our data on the effects of this fatty acid on the Ca²⁺-dependent permeability of artificial lipid membranes (BLM and liposomes). Based on these series of experiments we conclude that the formation of the PAL-induced pore is connected with ability of PAL to form a complex with Ca²⁺ in membrane.

    The PAL-induced pore is short-lived and closes spontaneously. We have shown that this is accompanied by recovery of the membrane potential of the inner mitochondrial membrane. Opening of PAL/Ca²⁺-activated, short-lived pores results in the CsA-insensitive release of cytochrome c from mitochondria. The addition of cytochrome c to mitochondria promoted fast recovery of mitochondrial membrane potential after depolarization induced by opening of PAL/Ca²⁺-activated pores, but not in case of opening of PTP. These results suggest that in addition to the PTP there are PAL/Ca²⁺-activated pores in mitochondria. This pore is thus likely to be a trigger of PAL-induced apoptosis and can be related to some pathologies, e.g. myocardial ischemia. We found that heaviness of myocardial infarction of ischemic patients correlates directly with the content of PAL in human blood serum.

     Supported by grants from the Medical Society of Finland and the Magnus Ehrnrooth Foundation (Saris), by a grant from RFBR (04-04-97281; Mironova), and by a grant from Russian Ministry of Education (А04-2.12-1116; Belosludtsev).

1.    Kong JY, Rabkin SW (2000) Palmitate-induced apoptosis in cardiomyocytes is mediated through alterations in mitochondria: prevention by cyclosporin A. Biochim. Biophys. Acta 1485: 45-55.

2.    Mironova GD, Gritsenko E, Gateau-Roesch O, Levrat C, Agafonov A, Belosludtsev K, Prigent AF, Muntean D, Dubois M, Ovize M (2004) Formation of palmitic acid/Ca²⁺ complexes in the mitochondrial membrane: a possible role in the cyclosporin-insensitive permeability transition. J. Bioenerg. Biomembr. 36: 171-178.

3.    Mironova GD, Gateau-Roesch O, Levrat C, Gritsenko E, Pavlov E, Lazareva AV, Limarenko E, Rey C, Louisot P, Saris NE (2001) Palmitic and stearic acids bind Ca²⁺ with high affinity and form nonspecific channels in black-lipid membranes. Possible relation to Ca²⁺-activated mitochondrial pores. J. Bioenerg. Biomembr. 33: 319-331.