Mitochondria Revisited. Alternative Functions of ... - Bioscience Reports

Bioscience Reports, Vol. 17, No. 6, 1997

REVIEW

Mitochondria Revisited. Alternative Functions of Mitochondria Dmitry B. Zorov,1-4 Boris F. Krasnikov,1-2 Alevtina E. Kuzminova,1 Michail Yu. Vysokikh,1 and Ljubava D. Zorova3 Received November 17, 1997 This review explores the alternative functions of mitochondria inside the cell. In a general picture of mitochondrial functioning, the importance and uniqueness of these intrinsic functions make them irreplaceable by other intracellular compartments. Among these are, participation in apoptosis and cellular proliferation, regulation of the cellular redox state and level of second messengers, heme and steroid syntheses, production and transmission of a transmembrane potential, detoxication and heat production. In most of the listed functions, reactive oxygen species modulate a number of non-destructive cellular activities. Some of the mitochondrial functions are reviewed in detail. KEY WORDS: Mitochondria; apoptosis; oxygen radicals; benzodiazepine receptor; mitochondrial; redox state; cellular; permeability transitions. ABBREVATIONS: ROS, reactive oxygen species; MCC, multi conductance channel; FTP, permeability transition pore; mBDR, mitochondrial benzodiazepine receptor; VDAC, voltage-dependent anion channel; SOD, superoxide dismutase; TNF, tumor necrosis factor; AA, arachidonic acid.

INTRODUCTION The main function of mitochondria is thought to be supplying the cell with energy. The great progress in understanding mitochondrial energetics has caused alternative mitochondrial functions to be ignored. Although the mitochondrion is a major source of energy for the cell under aerobic conditions, it is also responsible for a number of other functions which are not linked directly to energy production. The importance of these alternative functions has not been fully appreciated albeit there were attempts in past to specify some of these functions [1,2]. Some of these functions are unique and cannot be compensated for by other cellular systems. In Fig. 1 we schematically present a variety of mitochondrial functions. The cartoon 'A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russia. International Laser Center, Moscow State University, Moscow 119899, Russia. 'Biological Faculty, Moscow State University, Moscow 119899, Russia. 4To whom correspondence should be addressed. 507 0144-8463/97/1200-0507$12.50/0 © 1997 Plenum Publishing Corporation

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illustrates importance of mitochondriology, of which bioenergetics may be only one, although significant, part. The overwhelming majority of functions presented in Fig. 1 is implied to involve reactive oxygen species (ROS).

MITOCHONDRIA AND APOPTOSIS Apoptosis, or cellular suicide, seems to aim at removing a physiologically unwanted cell. The mechanism of such a selection is intriguing and still far from being completely understood. The participation of mitochondrial channels in programmed cellular death was predicted years ago. In 1992 Zorov et al. [3] suggested that cyclosporine A-sensitive channels (MCC) "function in programmed mitochondrial destruction". In 1993 Duchen et al. [4] and Griffiths and Halestrap [5] reported on the use of cyclosporine A as a defense against oxidative stress in vivo. In 1996 the release of a deadly factor from mitochondria undergoing permeability transitions was confirmed with different suggestions on the nature of this factor [6, 7], It became clear that permeability transition pore (PTP) might be significant in the chain of apoptotic events. It seems that mitochondrial destruction precedes or at least occurs at the same time as the cellular death. However, in contrast to necrotic death, when the cell plays a passive role in a process of a cell execution, apoptosis is a self-executing active process requiring energy for the cell to be executed (reviewed in [8]). One point to be emphasized is the obligatory requirement of functional mitochondria to provide complete cell execution. If we accept that mitochondria are necessary for the progress of apoptosis, then we conclude that PTP, although a necessary step in apoptotic pathway, may be transient. It might coincide with the observed drop of the mitochondrial membrane potential [9]. (An alternative explanation may be in the coexistence of two mitochondrial populations, one, very fragile, easily opens PTP and serves for initiating apoptotic events, while the second supplies the process with energy; the percentage of the first population may be very low.). One in vitro way to close PTP is to quickly chelate of calcium ions in extramitochondrial milieu. Another way is by supplementing mitochondria in situ with a cyclosporine A-resembling drug of natural origin. Thus, the assumption of an involvement of PTP in apoptosis demands an assumption of a cellular PTP regulator. Since there are many facts showing the organization of PTP within mitochondrial contact sites and/or a mitochondrial benzodiazepine receptor (mBDR), it is possible to search for it or them among members of contact sites or around them. At least three factors of a proteinous nature, which may be regarded as PTP regulators, have already been reported, modulator of VDAC (voltage-dependent anion channel) [10], hexokinase [11], and cyclophilin [12]. We would also add to this list bel-2 which is definitely in close proximity to the contact site. We will discuss the bcl-2 function in the following sections. We have to admit that all the listed arguments are still valid only for mitochondria in vitro. But, if the pore is transient, the short-term lived PTP can scarcely contribute to the process of ROS elimination in apoptosis through the respiratory activation.

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It seems that at least in some cases the apoptotic chain uses PTP as its necessary step. Recently, we were able to present data on a viral induced PTP in mitochondria [13], which may be relevant to the virus-induced apoptosis [14, 15]. The olligatory involvement of ROS at the onset of apoptosis is still controversial, since cells can undergo apoptotis even when they are cultured at low oxygen tensions [16]. We recently succeeded in consistently inducing PTP in rat liver mitochondria under extremely low pO2 [17]. Some apoptotic activators used are of steroid origin, which already implies mitochondrial involvement. This process will be described in detail in the section STEROID SYNTHESIS. The latest discoveries in this field have almost formed a dogma that mitochondrion is necessary for apoptotisis. However we actually still have to decide if mitochondria serve to promote or to prevent apoptosis. This provocative question will be examined later in the section about the role of mitochondrial pyridine nucleotides in cellular activity. MITOCHONDRIA AS A SOURCE OF FREE RADICALS It is not the aim of this paper to extensively review the contribution of mitochondria to the production of free radicals in the cell. Mechanisms of the damaging effects caused by activated oxygen species have been extensively studied and described in detail elsewhere (reviewed, for example, in [18 and 19]). Without presenting a formal scheme showing the chain of generation and transformation of ROS, we will restrict ourselves to listing the most important members of the ROS family. Among them, first of all, hydrogen peroxide, superoxide anion radical, hydroxyl radical and singlet oxygen should be mentioned. (The whole list of biologically active ROS is much wider [20]). Potentially the most destructive is hydroxyl radical, which is the strongest oxidant among the members of this family. The evidence of the involvement of ROS in oxidative stress and its relevance to some degenerative disorders were obvious enough to form a dogma on ROS as destructive intracellular elements. Apparently ROS can be regarded as cellular messengers. They have been included in the list of the most important signaling molecules in many cellular responses. H 2 O 2 , for example, can (i) activate glucose transport, lipid synthesis, calcium release from mitochondria, release of arachidonate from phospholipids, insulin receptor tyrosine kinase, pyruvate dehydrogenase activities, and (ii) suppress glycolysis, lipolysis, reacylation of lysophosphoiipids, ATP synthesis, superoxide dismutase and protein kinase activity (reviewed in [21]). A new perspective was opened when ROS were found to act as transcription activators of the stress-inducible genes. The nuclear transcription factor NF-kB in higher eucaryotes is known to activate the transcription of protective genes participating in inflammation and infection in response to different stimuli. The mechanism involves the conversion of cytosolic inactive form to the active one through the release and proteolitical degradation of the part of the inactive multiprotein complex (I-kB), subsequent translocation to the nucleus, binding to DNA and induction of gene expression. There are numbers of known stimuli of such conversion, namely

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H2O2, viruses, heat shock, cytokines such as TNF (tumor necrosis factor) and IL-1 (interleukin-1), and some others. At least some of the listed factors require ROS as an intermediate. For TNF, IL-1 and phorbol esters this is already an accepted fact (reviewed in [22]). The reasons for considering ROS as cellular messengers are simple. They have small size, and limited lifetime, are ubiquitous in cells, and precisely regulated by both production and degradation. In the next chapter we want to emphasize the importance of mitochondrial functioning as a well tuned machine regulating ROS level in a living cell being coupled to many important mitochondrial and cellular activities. Such regulation of intracellular ROS level, which we consider as the important second messengers, may reflect the maintaining by mitochondria of a principle multet nocem (excess is harmful). MITOCHONDRIAL REGULATION OF A LEVEL OF SECOND MESSENGERS Even a quick glance at a list of known second messengers can convince anyone that mitochondria can be involved. Let us examine some of the commonly known messengers (Fig. 1). In addition to producing the superoxide anion radical, mitochondria can also scavenge it. The effect was observed in vitro when isolated respiring mitochondria scavenged O2 generated by xanthine/xanthine oxidase [23]. The scavenging activity is proportional to the mitochondrial respiration rate and represents non-enzymatic process [23]. Also, there are data showing inhibition of cellular superoxide generation by some steroids produced inside mitochondria [24]. Nitric oxide, a free radical with a half-life of only few seconds (from 3 to 30) is a very potent physiological modulator. It is involved in neurotransmission [25], smooth muscle relaxation [26], inflammation [27], cell-mediated immune response [28] and has potentially genotoxic effects through direct modification of DNA bases [29]. The short half-life of NO is supposed to be the result of its high reactivity with oxygen [30]. Since intracellular pQ2 to a large extent depends upon mitochondrial activity, the latter definitely must be included in the list of potential regulators. At the same time, another way of NO scavenging is in its trapping by superoxide, thus forming peroxynitrite (note that both messengers are neutralized simultaneously). The product itself is relatively stable, but it can give an acidic form, producing NO2 and HO' [31], although the yield of the latter is low enough to not be considered as a cytotoxic agent [32]. It is noteworthy that NO-forming compounds displace mBDR ligand, Ro54864 from membrane preparation [33]. Figure 1 illustrates how multifunctional mBDR can be. In addition to its involvement in the process of porphyrin and steroids synthesis, there is increasing number of indications to its participation in the antioxidant pathway. Very strict correlation exists between the ability to resist H2O2 cytotoxity and the level of mBDR expression [34]. The observed similarity in the expression of both the mBDR gene and bcl-2 proto-oncogene suggests close proximity of their products. Since bcl-2 product can be regarded as an antioxidant through


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Fig. 1. The most important mitochondrial functions. Front panel of each box, macro-effects of mitochondria on the cellular activity. Right side of a box, microenvironment (some of the significant factors involved in a function). Upper sides of a box, the resulting effect(s). Note factors overlapping on all sides of box as a lack of understanding the causality. * For steroidogenic tissues only.

mediated decrease of ROS production and lymphocytes transfected with human mBDR cDNA are able to resist to H 2 O 2 , they can work either together [34] or independently. The second suggestion seems to be right if we accept that bcl-2 protects against cell death independently of ROS production [35, 36]. The homology of mammalian mBDR to CrtK protein from Rhodobacter capsulatus is further evidence

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in support of the involvement of mBDR in antioxygen defense since CrtK is supposed to be a site for the docking of the enzymes involved in carotenoid synthesis [37]. It is known that mitochondria can /3-oxidize fatty acids, some of which can be considered as second messengers [38]. Beside this, mitochondria can release fatty acids as a result of a Ca2+ load or ROS exposure [39]. Of these, polyunsaturated fatty acids are of great importance [40]. One of these, namely arachidonic acid (AA), transforms into prostaglandins coupled to a burst of O2 production in the presence of NAD(P)H [41]. There is direct evidence that arachidonate metabolism is an essential part of cell damage and apoptotic cell death and we will present few examples supporting this important statement. TNF-induced cytolysis was inhibited when A A metabolism was suppressed [42]; bcl-2 inhibition of the TNF-induced apoptosis was explained by the inhibition of A A metabolism [43]. Inhibitors of phospholipase A2 and cyclooxygenase prevented the hepatotoxin-induced rise in cytosolic free Ca 2t , activation of phospholipase A2 and resulting cell injury [44]. Reperfusion injury was involved with enhanced prostaglandin biosynthesis [45]. Radiolabeled AA and eicosanoids were released into the medium a few hours prior to the onset of cell death [46]. All these and other data demonstrate that the precise mitochondrial regulation of both fatty acids synthesis and fatty acids formation from the phospholipids may be one of the way for fine regulation of the cellular metabolism. MITOCHONDRIA AND CELLULAR REDOX STATE, DNA REPAIR AND PROLIFERATION When mitochondria oxidize substrates, they inevitably change the cellular redox state since they use reduced equivalents and the mitochondrial pool of these equivalents represents a significant part of the total cellular pool. Under normal conditions, pyridine nucleotides inside mitochondria are more reduced than in cytosol. According to Sahlin [47. 48] mitochondria of skeletal muscle possess up to 99% of the total NADH i.e., in range 0.09-0.35 mmol/kg • dry wt. (it almost doubles under a high physical load). These data are close to those reported by La Noue et al. [49] who gave for total mitochondrial content of (NAD + + NADH) a meaning of 6.2 mmol/ mg • protein. If we accept that 1 mg of mitochondrial protein roughly occupies 1 n\, the concentration of the couple (NAD + + NADH) in the mitochondrial matrix of a muscle cell would reach a meaning of a few mM. In liver the contents of mitochondrial NADH and NADPH are 0.3-0.8 and 2.5-3.5 nmol/mg protein, which are also in the range of mM concentrations in the matrix [50]. In cytosol the content of NADH does not exceed a few percent of the total cellular NADH. The NADH/NAD + ratio in heart cytosol gives the meaning of a standard redox potential -226 mV (inside mitochondria -354 mV) [51]. Apparently mitochondria retain the major part of the cellular (NAD + + NADH). Such a disproportional distribution of pyridine nucleotides between mitochondria and cytosol may have a very significant impact on cellular activity. When the cell provokes conditions optimal for opening PTP in mitochondria, the total mitochondrial pool of pyridine nucleotides will be oxidized and a part of the NAD+ formed will be released into cytosol, thus severely shifting the intracellular redox


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state. To illustrate this, we have placed a box in the scheme (Fig. 1) showing the regulation of the cellular redox state by mitochondria through the mitochondriacytosol cross-talk with pyridine nucleotides and glutathione. No doubt, the massive release of oxidized NAD + into cytosol will cause the dramatic change of most enzymatic reactions (including mitochondrial ones), among which the control of gene expression [52] is of great importance when the cell undergoes apoptosis. NAD+ released from mitochondria may also change the activity of electron transport chains existing in the outer membrane of a nuclear envelope. These chains use NADH or NADPH as substrates. Nuclear envelope electron transport chains resemble microsomal mixed-function oxidase, but with lower activity. They may be involved in the ROS formation. A very indicative example is given by the strong antineoplastic drug bleomycin, which, when in complex with Fe and in the presence of NADH, induces DNA damage in isolated nuclei through the activation of NADH-cytochrome b5 reductase. The latter generates ROS which oxidize both deoxyribose and DNA bases [53]. Bleomycin-induced high levels of single- and double-strand breakage in DNA molecules have been found [53]. Double-strand breakage was greatly increased in the presence of NADPH or NADH; iron-containing compounds dramatically increase DNA fragmentation [54]. It is now accepted that bleomycin belongs to the classical inducers of apoptosis [55]. When nuclei were incubated with hydroperoxides and related drugs, a number of radicals were detected; the process of radical generation was shown to be an enzymatic reaction involving haemoproteins (in particular cytochrome P-450) and NADPH-cytochrome P-450 reductase [56]. Pyridine nucleotide-dependent generation of radicals is highly dangerous for the cellular DNA considering its close proximity to the generation site. The ROSproducing activity of nuclear membranes possibly changes under the influence of redox partners released from mitochondria after PTP opening. At least two can interact with the nuclear redox chain, pyridine nucleotides and cytochrome C. The latter was recently shown to be an obligatory factor in activating apoptosis [7, 57, 58]. More than 30 years ago three Russians (Archakov, Kariakin, and Skulachev) described intermembrane communication between mitochondrial and microsomal electron transport chains through cytochrome b5 [59]. Twenty years ago the interaction between the outer and inner mitochondrial membranes was demonstrated through the shuttling of cytochrome C ([60] and reviewed in [2]). By conceiving these two models, it seems possible that there is an interaction of mitochondrial and nuclear electron carriers, which generates ROS by nuclear, as well as microsomal, redox chains. But the speculative pictures drawn above have another meaning which could change our understanding of the apoptotic chain of events. It is known that DNA strand breakage induced by chemical and physical factors activates the compensative process of fragmented DNA reparation. The DNA excision-repair process is accompanied by a proportional loss of NAD required for poly(ADP-ribose) synthesis [61]. In this case, an increased number of DNA strands break formation, which results in the dramatic decrease of the cellular NAD (as well as ATP) level

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and which may be lethal for the cell. Here we face a paradox—if the activation of poly(ADP-ribose) synthase necessary for reparating DNA fragmentation induced by oxygen radicals is prevented [62], the cell can survive. This can explain the cause of ROS-stimulated cell death which can be reduced to NAD* depletion. (A similar suggestion implies that depletion of intracellular reduced glutathione, liberated from mitochondria undergoing apoptosis is a cause of apoptosis [63]). Poly(ADP-ribose) polymerase definitely plays a key role in apoptosis since Ca/Mg-dependent endonuclease, which is apparently involved in apoptosis, is latent when poly-ADP-ribosylated. The onset of apoptosis requires a removal of the polymer from the endonuclease to activate it. If this is true, mitochondria seem to act with self-sacrifice to release mitochondrial NAD+ to repair damaged genetic apparatus. Note, that mtDNA repair machinery also requires NAD + for its activity, although there were data showing low reparing activity for mitochondrial DNA comparative to nuclear DNA [64]. Intramitochondrial oxidation of pyridine nucleotides due to either mild uncoupling or PTP opening can be considered as preferential for repairing a damaged mitochondrial genome. As we said earlier, the mitochondrial role in cellular death may be controversial. We already mentioned that the transient depolarization of the inner mitochondrial membrane takes place prior to some types of apoptosis [6]. A significant amount of data shows that mitochondria release some deadly factor [6, 7, 57, 58]. We suggested (see section MITOCHONDRIA AND APOPTOSIS) that mitochondria should be resealed to support energy-dependent apoptosis or that the population of energized mitochondria within a cell should coexist with mitochondria with PTP; part of a population with PTP should work to initiate apoptosis, while another intact part should provide an energy. (Such a situation is unlikely when isolated mitochondria are in suspension due to the chain of one by one openings in mitochondrial population.) Ca2+- and ATP-dependent activity of endonucleases results in a fragmentation of DNA moiety, which in turn demands NAD + to repair. Here the second opening of PTP may result in a transient rise of NAD* in cytosol. STEROID HORMONE SYNTHESIS IN THE ADRENAL CORTEX In the scenario in Fig. 2, the adrenal cortex mitochondrion is as useful as cytosol in steroid synthesis. The sketch presents only the general idea of mitochondrial involvement in steroid synthesis. The important point is that the transport of steroid intermediates across mitochondrial membranes requires the participation of mBDR (for reviews, see [65, 66]). The rate-limiting step in a net steroid production is thought to be a translocation of cholesterol from the outer to the inner membrane, which is under the control of mBDR ligands [67], while low concentrations of the mitochondrial matrix Ca2+ regulate P-450scc-dependent cholesterol metabolism [68]. It has been demonstrated that while the conversion of cholesterol to pregnenolone (catalyzed by mitochondrial P-450SCC) is not inhibited until pO2 is very low, the conversion of corticosterone to aldosterone (catalyzed by mitochondrial P-450aWo) is O2-sensitive [69]. At the same time, the intramitochondrial process of NADPH oxidation coupled with substrate hydroxylation (this is the case for catalyzed by

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Fig. 2. General scheme of the steroid hormone biosynthesis in the adrenal cortex mitochondria.

P-450 hydroxylation of steroids presented above) was accompanied by superoxide formation. The latter was due to the electron leakage from P-450SCC. It should be noted that C-19 and C-21 steroids with lla-OH groups (l la-OH-testosterone and 1 la-OH-cortisol) decreased leakage and those with 1 Ib-OH groups (1 Ib-OH-testosterone and cortisol) stimulated both NADPH oxidation and H2O2 formation [70]. It supports the function of the mitochondrial P-450 system as a significant source of oxygen radicals. At the same time, oxygen radicals were shown to function as intracellular regulators of steroid biosynthesis [71], which might be an indicative example of a nondestructive ROS functioning. HEME SYNTHESIS Figure 3 illustrates how mitochondrion shares significance with cytosol in heme biosynthesis. Some role in this process has been attributed to mBDR. Apparently, mBDR may play this role through the regulation of import of heme precursors. It is known that the affinity of protoporphyrin IX to mBDR is in the nanomolar range [72], thus placing this intermediate to the row of a potent natural ligand of mBDR. The obvious similarity of the pictures presented in Figs. 2 and 3 is striking; note that both processes depicted in the figures are relevant to the function of mBDR. CELLULAR PROLIFERATION Participation of mitochondria in the cell proliferation has been long ago implied. In the previous section, when discussing the role of mitochondria in the cellular redox status, we reserved for them a major role in regulating cellular redox

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Fig. 3. General scheme of the heme biosynthesis.

status through the control of the cellular pool of pyridine nucleotides. Once again we must emphasize the importance of a cellular redox state in regulating a gene expression which is the most significant factor in a cellular proliferative activity [52]. Beside this, mitochondria produce such modulators of gene expression as steroid hormones (see section on Steroid Hormone Synthesis). The conversion of estrogens to reactive metabolites which bind to nuclear proteins and DNA requires NADPH, nuclear cytochrome P-450 and peroxides [73, 74]. In mouse lymphocytes, the mitogen concanavalin A causes doubling of the cellular NAD+ concentration used as a substrate of the ADP ribose polymerase [75]. Inhibitors of ADP ribosylation block cell proliferation as well as the DNA repair process. These data show that the mitochondrial NAD* pool can also be an important factor in a cellular proliferation (see corresponding box in Fig. 1). By an unknown reason, it is necessary to repair DNA strand breaks to trigger proliferation. The correlation between the intracellular level of NAD + and DNA repair and cell proliferation is very high (r= 0.93 and 0.96 correspondingly) [76]. Mitochondrial membranes are known to be the sites for docking of some proteins (bcl-2, prohibitin and others) participating in proliferative response, bcl-2, while carrying anti-apoptotic properties, seems to be involved in cellular proliferation [77]. Prohibitin regulating the entry of the cell into S-phase is also localized in mitochondria [78, 79]. The list of arguments in support of the importance of mitochondria in cellular proliferation can be supplemented with the data demonstrating strong antiproliferative properties of ligands to the mitochondrial benzodiazepine receptor [80, 81], as well as the modulation of the proliferation by cyclosporine A [82, 83]. The latter data are relevant to the suggestions that (i) the inserts of mitochondrial DNA into nuclear genome contribute to cellular transformation [84], and (ii) release of mtDN A from mitochondria can occur via PTP [85, 86]. One can speculate that nuclearmitochondrial cross-talk might be involved in the signaling of proliferation. It is shown that mitochondria interact with cytoskeleton elements (reviewed in [87]) and

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that cytoskeleton is involved in proliferative response. The linkage between nucleus and mitochondrion can provide a physical base for such intracellular interaction. It is known that in mitochondria, endoplasmic reticulum and nuclei possess Catransporting systems [88, 89]. Ca-supported mitochondrial PTP is supposed to be regulated by rotamase-carrying immunophilin, mitochondrial cyclophilin; calcium release channel from sarcomplasmic reticulum (ryanodine receptor) is tightly bound to another rotamase-carrying immunophilin, FK-506-binding protein; inositol triphosphate-mediated Ca transporter is located in the inner nuclear membrane [90] with close proximation to FK-506 binding proteins [91, 92, 93]. These three named compartments are the main sources of ROS generation and all three are inhabited by bcl-2 [94]. Recently, a very tight link of Ca sequestration by mitochondria and bcl-2 activity was found in mitochondria [95].

MITOCHONDRIAL PRODUCTION AND TRANSMISSION OF THE MEMBRANE POTENTIAL Information on the cellular role of mitochondrial electric potential is both scattered and scanty. But it seems to be one of the most important factors in cellular homeostasis. For some reason, mitochondria still retain some membrane potential for a while under conditions unfavorable for its production (blockage of the electron transport chain either by inhibitors or by lack of oxygen) [96]. That means that mitochondrion spends ATP to support the electrical potential when it is unable to make it by respiration. The involvement of the mitochondrial membrane potential in the apoptotic cellular death has been discussed above 6, pointing to the importance of the potential in a cellular homeostasis. In extended mitochondrial systems the mitochondrial membrane potential can easily be transmitted to the distant parts of a cell [97], thus supplying the ground to maintain such homeostasis. One more function was proposed for mitochondrial electrochemical proton potential, namely to regulate the process of mtDNA repair [98].

ACKNOWLEDGMENT This work was supported by grants from Russian Foundation of Basic Research (96-04-49384 and 96-04-50940).

REFERENCES I. 2. 3. 4.

5.

Skulachev, V. P. (1962) Interrelationship of the Respiratory Chain Reactions and Phosphorylation. Moscow, USSR Akad. Sci. Publ. Skulachev, V. P. (1988) Membrane Bioenergetics. Berlin: Springer. Zorov, D. B., Kinnally, K. W., and Tedeschi, H. (1992) J. Bioenerg. Biomembr. 24:119-124. Duchen, M. R., McGuiness, O., Brown, L. A., and Crompton, M. (1993) Cardiovusc. Res. 27:17901794. Griffiths, E. J. and Halestrap, A. P. (1993) J. Mol. Cell. Cardiol. 25:1461-1469.

518


6. 7. 8. 9. 10. 11, 12. 13. 14. 15.

Marchetti, P. et al. (1996) J. Exp. Med. 184:1155-1160. Liu, X., Kim, C. N., Yang, J., Jemmerson, R., and Wang, X. (1996) Cell 86:147-157. Denmeadde, S. R. and Isaacs, J. T. (1996) Cancer Control 3:303-309. Zarazami, N. et al. (1995) J. Exp. Med. 181:1661-1672. Liu, M. Y. and Colombini, M. (1992) J. Bioenerg. Biomembr. 24:41-46. Lane, M. D., Pedersen, P. L., and Mildvan, A. S. (1986) Science 234:526-527. Halestrap, A. P. and Davidson, A. M. (1990) Biochem. J. 268:153-160. Zorova, L. D. et al. (1997) Biophys. J. 72 N2:A39. Tropea, F. et al. (1995) Exp. Cell. Res. 218:63-70. Terai, C., Kornbluth, R. S., Pauza, C. D., Richman, D. D., and Carson, D. A. (1991) J. Clin. Invest. 87:1710-1715. Slater, A. F., Stefan, C., Nobel, I., van den Dobbelsteen, D. J., and Orrenius, S. (1995) Toxicol. Lett. 82-83:149-153. Kuzminova, A. E., Krasnikov, B. F., and Zorov, D. B. (1997) Biophys. J. 72 NS:A39. Skulachev, V. P. (1996) Q. Rev. Biophys. 29:169-202. Farber, 3. L. (1994) Environ. Health Perspect. 102 (Suppl. 10): 17-24. Khan, A. U. and Wilson, T. (1995) Curr. Biol. 2:437^45. Ramasarma, T. (1990) Ind. J. Biochem. Biophys. 27:269-274. Remade, J., Raes, M., Toussaint, O., and Rao, G. (1995) Mutat. Res. 316:103-122. Guidot, D. M. et al. (1995) J. Clin. Invest. 96:1131-1136. Mohan, P. F. and Jacobson, M. S. (1993) Am. J. Med. Sci. 306:10-15. Ross, C. A., Bredt, D., and Snyder, S. H. (1990) Trends Neurosci. 13:216-222. Tare, M., Parkinson, H. C., Coleman, H. A., Nelid, T. O., and Dusting, G. J. (1990) Nature 346:69-

16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26.

71.

27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40.

41. 42. 43. 44. 45. 46.

47. 48. 49. 50. 51. 52.

Kubrina, L. N., Mordvintsev, P. I., and Vanin, A. F. (1989) Bull. Exp. Biol. Med. 107:31-37. Liew, F. Y. and Cox, F. E. (1991) Immunol. Today 12: A17-21. Liu, R. H. and Hotchkiss, J. H. (1995) Mutat. Res. 339:73-89. Taha, Z., Kiechle, F., and Malinski, T. (1992) Biochem. Biophys. Res. Comm. 188:734-739. Pryor, W. A. and Squadrito, G. L. (1995) Am. J. Physiol. 268: L699-722. Pou, S., Nguyen, S. Y., Cladwell, T., and Rosen, G. M. (1995) Biochim. Biophys. Acta 1244:62-68. Weissman, B. A., Bolger, G. T., and Chiang, P. K. (1990) FEBS Lett. 260:169-172. Carayon, P. et al. (1996) Blood87:3170-3178. Jacobson, M. D. and Raff, M. C. (1995) Nature 374:814-816. Shimizu, S., Eguchi, Y., Kosaka, H., Kamiike, W., Matsuda, H., and Tsujimoto, Y. (1995) Nature 374:811-813. Baker, M. E. and Fanestil, D. D. (1991) Cell 65:721 -722. Reubsaet, F. A., Veerkamp, J. H., Trijbels, J. M., and Monnens, L. A. (1989) Lipids 24:945-950. Malis, C. D., Weber, P. C., Leaf, A., and Bonventre, J. V. (1990) Proc. Natl. Acad. Sci. U.S.A. 87:8845-8849. Chan, P. H., Fishman, R. A., Schmodley, J. W., and Chen, S. F. (1984) J. Neurosci. Res. 12:595605. Grisham, M. B. and Granger, D. N. (1989) Clin. Chest Med. 10:71-81. Matthews, N., Neale, M. L., Jackson, S. K., and Stark, J. M. (1987) Immunology 62:153-155. Jaattela, M., Benedict, M., Tewari, M., Shayman, J. A., and Dixit, V. M. (1995) Oncogen 10:22972305. Horton, A. A. and Wood, J. M. (1989) Eicosanoids 2:123-129. Karmazin, M. (1985) Adv. Myocardiol. 6:429^136. Knauer, M. F., Longmuir, K. J., Yamamoto, R. S., Fitzgerald, T. P., and Granger, G. A. (1990) J. Cell. Physiol. 142:469-479. Sahlin, K. (1985) Pflug. Arch. 403:193-196. Sahlin, K. and Katz, A. (1986) Biochem. J. 239:245-248. La Noue, K. F., Bryla, J., and Williamson, J. R. (1972) J. Biol. Chem. 247:667-679. Siess, E. A., Banik, E., and Neugebauer, S. (1988) Eur. J. Biochem. 173:369-374. Hassinen, I. E. (1986) Biochim. Biophys. Acta 853:135-151. Allen, J. F. (1993) J. Theor. Biol. 165:609-631.


519

53. Kappus, H., Mahmutoglu, I., Kostrucha, J., and Scheulen, M. E. (1987) Free Radical Res. Commun. 2:271-277. 54. Byrnes, R. W. and Petering, D. H. (1994) Biochem. Pharmacol. 48:575-582. 55. Hamilton, R. F. Jr., Li, L., Felder, T. B., and Holian, A. (1995) Am. J. Physiol. 269:1318-325. 56. Greenley, T. L. and Davies, M. J. (1994) Biochim. Biophys. Acta 1226:56-64. 57. Kluck, R. M., Bossy-Wetzel, E., Green, D. R., and Newmeyer, D. D. (1997) Science 275:1132-1136. 58. Yang et al. (1997) Science 275:1129-1132. 59. Archakov, A. I., Karyakin, A. V., and Skulachev, V. P. (1974) FEBS Lett. 39:239-242. 60. Mokhova, E. N., Skulachev, V. P., and Zhigacheva, I. V. (1977) Biochim. Biophys. Ada 501:415423. 61. Carson, D. A., Carrera, C. J., Wasson, D. B., and Yamanaka, H. (1988) Adv. Enz. Regul. 27:395404. 62. Marini, M., Frabetti, F., Brunelli, M. A., and Raggi, M. A. (1993) Biochem. Pharmacol. 46:21302144. 63. Slater, A. F., Nobel, C. S., and Orrenius, S. (1995) Biochim. Biophys. Ada 1271:59-62. 64. Richter, C. (1988) FEBS Lett. 241:1-5. 65. Kruger, K. E. (1995) Biochim. Biophys. Ada 1241:453-470. 66. Kruger, K. E., Papadopoulos, V. (1992) Annu. Rev. Pharmacol. Toxicol. 32:211-237. 67. Kruger, K. E., Papadopoulos, V. (1990) J. Biol. Chem. 265:15015-15022. 68. Yamazaki, T., Kowluru, R., McNamara, B. C., and Jefcoate, C. R. (1995) Arch. Biochem. Biophys. 318:131-139. 69. Raff, H. and Jankowski, B, (1995) J. Appl. Physiol. 78:1625-1628. 70. Rapoport, R., Sklan, D., and Hanukoglu, I. (1995) Arch. Biochem. Biophys. 317:412-416. 71. Carlson, J. C., Wu, X. M., and Sawada, M. (1993) free Radicals Biol. Med. 14:79-84. 72. Snyder, S. H., Verma, A., and Trifiletti, R. (1987) FASEB J. 1:282-288. 73. Roy, D. and Thomas, R. D. (1994) Arch. Biochem. Biophys. 315:310-316. 74. Roy, D. and Pathak, D. N. (1993) Bioch. Molec. Biol. Internal. 31:923-934. 75. Greer, W. L. and Kaplan, J. G. (1984) Biochem. Biophys. Res. Commun. 122:366-372. 76. Morgan, W. A. (1995) J. Biochem. Toxicol 10:227-232. 77. Hockenbery, D. M. (1995) Bioessays 17:631-638. 78. Ikonen, E., Fiedler, K., Parton, R. G., and Simons, K. (1995) FEBS Lett. 358:273-277. 79. McClung, J. K., Jupe, E. R., Liu, X. T., and Dell'Orco, R. T. (1995) Exp. Gerontol. 30:99-124. 80. Gamier, M. et al. (1993) Endocrinology 132:144-158. 81. Kunert-Radek, J., Stepien, H., and Pawlikowski, M. (1994) Neuroendocrinology 59:92-96. 82. Orosz, C. G., Roopenian, D. C., Widmer, M. B., and Bach, F. H. (1983) Transplantation 36:706711.

83. Masuhara, M., Ogasawara, H., Katayal, S. L., Nakamura, T., and Shinozuka, H. (1993) Carcinogenesis 14:1579-1584. 84. Richter, C. (1988) FEBS Lett. 241:1-5. 85. Zorov, D. B., Camp, M., Filburn, C. R., Hansford, R. G. (1996) Biophys. J. 64:A414. 86. Zorov, D. B. (1996) Biochemistry (Moscow) 61:939-946. 87. Leterrier, J. F., Rusakov, D. A., Nelson, B. D., and Linden, M. (1994) Microsc. Res. Techniq. 27:233261.

88. Gunter, T. E. and Pfeiffer, D. R. (1990) Am. J. Physiol. 258:755-786. 89. Lanini, L., Bachs, O., and Carafoli, E. (1992) J. Biol. Chem. 267:11548-11552. 90. Humbert, J. P., Mattar, N., Artault, J. C., Koppler, P., and Malviya, A. N. (1996) J. Biol. Chem. 271:478-485. 91. Jin, Y. J. and Burakoff, S. J. (1993) Proc. Natl. Acad. Sci. U.S.A. 90:7769-7773. 92. Perrot-Applanat, M., Cibert, C., Geraud, G., Renoir, 3. M., and Baulieu, E. E. (1995) J. Cell. Sci. 108:2037-2051. 93. Amnemri, E. S. et al. (1994) J. Biol. Chem. 269:30828-30834. 94. Krajewski, S., Tanaka, S., Takayama, S., Schibler, M. J., Fenton, W., and Reed, J. C. (1993) Cancer Res. 53:4701-4714. 95. Murphy, A. N., Bredesen, D. E., Cortopassi, G., Wang, E., and Fiskum, G. (1996) Proc. Nam. Acad. Sci. U.S.A. 93: 9893-9898.

520


96. DiLisa, F. et al. (1995) J. Phyxiol. 486:11 -13. 97. Amchenkova, A. A., Bakeeva, L. E.. Chentsov, Yu. S., Skulachev, V. P., and Zorov, D. B. (1988) J. Cell. Biol. 107:481-495. 98. Zorov, D. B. (1996) Biochem. Biophys. Ada 1275:10 15.