Svetlana A. Konovalova

Tl+ induces the permeability transition pore in Ca2+-loaded rat liver mitochondria energized by glutamate and malate

It is known that Ca2+ and heavy metals more actively induce MPTP opening in mitochondria, energized by the I complex substrates. Thus, a rise in a Tl+-induced MPTP was proposed in experiments on isolated rat liver mitochondria energized by the complex I substrate (glutamate and malate). Expose of the mitochondria to Ca2+ into a medium containing TlNO3, glutamate, and malate as well as sucrose or KNO3 resulted in a decrease in state 3, state 4, or DNP-stimulated respiration as well as an increase of both mitochondrial swelling and ΔΨmito dissipation. The MPTP inhibitors, CsA and ADP, almost completely eliminated the effect of Ca2+, which was more pronounced in the presence of the complex I substrates than the complex II substrate (succinate) and rotenone (Korotkov and Saris, 2011). The present study concludes that Tl+-induced MPTP opening is more appreciable in mitochondria energized by glutamate and malate but not succinate in the presence of rotenone. We assume that the Tl+-induced MPTP opening along with followed swelling and possible structural deformations of the complex I in Ca2+-loaded mitochondria may be a part of the thallium toxicity mechanism on mitochondria in living organisms. At the same time, oxidation of Tl+ to Tl3+ by mitochondrial oxygen reactive species is proposed for the mechanism.

Y3 +, La3 +, and some bivalent metals inhibited the opening of the Tl+-induced permeability transition pore in Ca2 +-loaded rat liver mitochondria

We showed earlier that diminution of 2,4-dinitrophenol (DNP)-stimulated respiration and increase of both mitochondrial swelling and electrochemical potential (ΔΨmito) dissipation in medium containing TlNO3 and KNO3 were caused by opening of Tl(+)-induced mitochondrial permeability transition pore (MPTP) in the inner membrane of Ca(2+)-loaded rat liver mitochondria. The MPTP opening was studied in the presence of bivalent metal ions (Sr(2+), Ba(2+), Mn(2+), Co(2+) and Ni(2+)), trivalent metal ions (Y(3+) and La(3+)), and ruthenium red. We found that these metal ions (except Ba(2+) and Co(2+)) as well as ruthenium red inhibited to the MPTP opening that manifested in preventing both diminution of the DNP-stimulated respiration and increase of the swelling and of the ΔΨmito dissipation in medium containing TlNO3, KNO3, and Ca(2+). Inhibition of the MPTP opening by Sr(2+) and Mn(2+) is suggested because of their interaction with high affinity Ca(2+) sites, facing the matrix side and participating in the MPTP opening. The inhibitory effects of metal ions (Y(3+), La(3+), and Ni(2+)), and ruthenium red are accordingly discussed in regard to competitive and noncompetitive inhibition of the mitochondrial Ca(2+)-uniporter. High concentrations (50μM) of Y(3+) and La(3+) favored of MPTP opening in the inner membrane of rat liver mitochondria in Ca(2+) free medium containing TlNO3. The latter MPTP opening was markedly eliminated by MPTP inhibitors (cyclosporine A and ADP).

Reversible metabolic depression in lamprey hepatocytes during prespawning migration: dynamics of mitochondrial membrane potential.

The lamprey (Lampetra fluviatilis L.) is an extant representative of the ancient vertebrate group of Agnathans. During the prespawning migration (the river period of life from autumn until spring) lamprey hepatocytes exhibit widely different energy states: a high-energy state in autumn and spring, corresponding to a normal physiological standard, and a low-energy state in winter, which is provoked by prolonged starvation and profound metabolic arrest. In spring the restoration of energy status (return to an active state) is associated with hormonally induced lipolysis of the lipid droplets stored in the cells. Lamprey hepatocytes demonstrate an aerobic metabolism based on oxidation of free fatty acids. The dynamics of mitochondrial membrane potential (MMP) were measured throughout the prespawning migration. Pharmacological inhibition of the electron transport chain decreased the MMP and caused extensive depletion of cellular ATP without loss of cell viability. The potential molecular mechanisms responsible for winter metabolic depression in lamprey hepatocytes are discussed.

Mitochondrial and lysosomal pathways of lamprey ( Lampetra fluviatilis L.) hepatocyte death

Mechanisms of mitochondrial and lysosomal pathways of natural death of lamprey hepatocytes are described at the spring period of the prespawn migration. The mitochondrial pathway (release of cytochrome c from mitochondria into cytosol and activation of caspases) is realized by the classic scheme of apoptosis. Comparatively recently, the lysosomal pathway of cell death associated with cathepsin B activation has been revealed in cells in pathologies, specifically in obstruction of gallbladder and bile ducts. A peculiarity of lamprey hepatocytes consists in that in the adult animal liver there takes place biliary atresia (the absence of gallbladder and bile ducts. Thereby, the lamprey hepatocytes are an excellent object for study of this new pathway of cell death. We have revealed development of the mitochondrial and the lysosomal pathways of cell death of lamprey hepatocytes.

Membrane potential of mitochondria in hepatocytes of the river lamprey Lampetra fluviatilis at periods of metabolic depression and activity

ISSN 0022-0930, Journal of Evolutionary Biochemistry and Physiology, 2011, Vol. 47, No. 1, pp. 97—99.

Mersalyl prevents the Tl + -induced permeability transition pore opening in the inner membrane of Ca 2+ -loaded rat liver mitochondria

It was earlier shown that the calcium load of rat liver mitochondria in medium containing TlNO3 and KNO3 resulted in the Tl+-induced mitochondrial permeability transition pore (MPTP) opening in the inner membrane. This opening was accompanied by an increase in swelling and membrane potential dissipation and a decrease in state 3, state 4, and 2,4-dinitrophenol-uncoupled respiration. This respiratory decrease was markedly leveled by mersalyl (MSL), the phosphate symporter (PiC) inhibitor which poorly stimulated the calcium-induced swelling, but further increased the potential dissipation. All of these effects of Ca2+ and MSL were visibly reduced in the presence of the MPTP inhibitors (ADP, N-ethylmaleimide, and cyclosporine A). High MSL concentrations attenuated the ability of ADP to inhibit the MPTP. Our data suggest that the PiC can participate in the Tl+-induced MPTP opening in the inner membrane of Ca2+-loaded rat liver mitochondria.

ATP-consuming processes in hepatocytes of river lamprey Lampetra fluviatilis on the course of prespawning starvation.

The work was performed to establish which of the major ATP-consuming processes is the most important for surviving of hepatocytes of female lampreys on the course of prespawning starvation. The requirements of protein synthesis and Na(+)-K(+)-ATPase for ATP in the cells were monitored by the changes in mitochondrial membrane potential (MMP) in the presence of corresponding inhibitors from the peak of metabolic depression (January-February) to the time of recovery from it (March-April) and spawning (May). Integrity of lamprey liver cells was estimated by catalytic activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in blood plasma. In January-February, the share of ATP necessary for protein synthesis was 20-22%, whereas before spawning it decreased to 8-11%. Functioning of Na(+)-K(+)-pump required 22% of cellular ATP at the peak of metabolic depression, but 38% and 62% of ATP in March-April and May, respectively. Progression of prespawning period was accompanied by 3.75- and 1.6-fold rise of ALT and AST activities in blood plasma, respectively, whereas de Ritis coefficient decreased from 2.51±0.34 to 0.81±0.08, what indicates severe damage of hepatocyte membranes. Thus, the adaptive strategy of lamprey hepatocytes to develop metabolic depression under conditions of energy limitation is the selective production of proteins necessary for spawning, most probably vitellogenins. As spawning approaches, the maintenance of transmembrane ion gradients, membrane potential and cell volume to prevent premature cell death becomes the priority cell function.