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At present, approaches to studying mitochondrial functions in malarial parasites are quite limited because of the technical difficulties in isolating functional mitochondria in sufficient quantity and purity. We have developed a flow cytometric assay as an alternate means to study mitochondrial functions in intact erythrocytes infected with Plasmodium yoelii, a rodent malaria parasite. By using a very low concentration (2 nM) of a lipophilic cationic fluorescent probe, 3,3dihexyloxa-carbocyanine iodide, we were able to measure mitochondrial membrane potential(⌬⌿ m ) in live intact parasitized erythrocytes through flow cytometry. The accumulation of the probe into parasite mitochondria was dependent on the presence of a membrane potential since inclusion of carbonyl cyanide m-chlorophenylhydrazone, a protonophore, dissipated the membrane potential and abolished the probe accumulation. We tested the effect of standard mitochondrial inhibitors such as myxothiazole, antimycin, cyanide and rotenone. All of them except rotenone collapsed the ⌬⌿ m and inhibited respiration. The assay was validated by comparing the EC 50 of these compounds for inhibiting ⌬⌿ m and respiration. This assay was used to investigate the effect of various antimalarial drugs such as chloroquine, tetracycline and a broad spectrum antiparasitic drug atovaquone. We observed that only atovaquone collapsed ⌬⌿ m and inhibited parasite respiration within minutes after drug treatment. Furthermore, atovaquone had no effect on mammalian ⌬⌿ m . This suggests that atovaquone, shown to inhibit mitochondrial electron transport, also depolarizes malarial mitochondria with consequent cellular damage and death.Plasmodium spp. are obligate intracellular parasites, spending a major portion of their life cycle within erythrocytes and converting these relatively inactive cells into metabolically thriving active hosts. At present, our knowledge of mechanisms by which the parasite accomplishes these changes is limited, as is our understanding of metabolic processes associated with parasitism. It is generally believed that glycolysis is the main source of ATP in erythrocytic stages of malarial parasites with little or no contribution by mitochondria to the cellular ATP pool (1, 2). A lack of tricarboxylic acid cycle enzymes (3-6) and an acristate mitochondrial morphology has led to the suggestion that mitochondria in malaria parasite act mainly to serve as an electron disposal sink for dihydroorotate dehydrogenase, a critical enzyme in pyrimidine biosynthesis (7-9). It is well established through studies in other systems that, in addition to oxidative phosphorylation, mitochondria are also central to many other physiological activities such as the metabolism of molecules such as amino acids, lipids, and heme, as well as intracellular Ca 2ϩ homeostasis (10). These functions are achieved by the action of gene products encoded by both mitochondrial and nuclear genomes. Because most of the mitochondrial proteins are encoded by the nuclear genome and imported into mitochon...

Respiring intact cells maintained an internal pH more alkaline by 0.63 -0.75 unit than that of the milieu at extracellular pH 7, both in growth medium and KCl solutions. The ApH decreased when respiration was inhibited by anaerobiosis or in the presence of KCN.The AGH, established by EDTA/valinomycin-treated cells, was constant (122 -129 mV) over extracellular potassium concentration of 0.01 mM -1 mM. At the lower potassium concentration A $ (110-120mV) was the predominant component, and at the higher concentration d p H increased to 0.7 units (42 mV). At 150 mM potassium A,EH was reduced to 70 mV mostly due to a d pH component of 0.89 (53 mV). The interchangeability of the A fiH components is consistent with an electrogenic proton pump and with potassium serving as a counter ion in the presence of valinomycin. Indeed both parameters of A ,EH decreased in the presence of carbonylcyanide p-trifluoromethoxyphenylhydrazone.The highest ApH of 2 units was observed in the intact cells at pH 6; increasing the extracellular pH decreased the ApH to 0 at pH 7.65 and to -0.51 at pH 9. A similar pattern of dependence of A pH on extracellular pH was observed in EDTA/valinomycin-treated cells but the d $ was almost constant over the whole range of extracellular pH values (6 -8) implying electroneutral proton movement.Potassium is specifically required for respiration of EDTA-treated E. coli K12 cells since other monovalent or divalent cations could not replace potassium and valinomycin was not required.It is established that an electrochemical proton gradient (dpH) is built up through energization across energy-conserving membranes of eucaryotic organelles -chloroplasts and mitochondria (reviews in [l] to [4]). The methods employed for determining AfiH in microscopic systems, recently critically reviewed [4], include determinations of the pH gradient (dpH) and the potential gradient (All/) across the membrane, since both parameters contribute to ApH according to the relation : Mitchell [5] suggested that this proton gradient is of primary importance in the mechanism of biological energy conversion.In the procaryotic cell, the cytoplasmic membrane is the site of energy coupling. Upon energization, outward translocation of protons from whole bacterial cells has been demonstrated showed that upon glycolysis intact cells of Strepto-COCCUS faecalis maintain a more alkaline internal pH (0.5-1 unit higher than the medium) and a potential of 150-200 mV across the membrane with the interior negative [lo]. Since both these parameters of dDH were not determined simultaneously, the magnitude of dpH and the relationship between its components can only be indirectly estimated for these cells. A membrane potential of about 140 mV was recently estimated in respiring E. coli cells [Ill but the ApH was not determined. While in chromatophore fractions obtained from photosynthetic bacteria A$ and dpH contribute equally to the ApH [12,13], in membraneous vesicles obtained from E. coli only A$ was detected [14,15].Recent studies showed that an a...

A method for the measurement of the internal pH of chloroplasts is described. The method is based on the uptake of a fluorescent amine by chloroplasts, which can be observed by the lowering of the fluorescence emitted from a suspension of chloroplasts.It is shown that this uptake is dependent, as expected, on the dissociation constant of the amine and also on the number of ionisable amines in the molecule. Amines attached to two types of chromophores, acridine and naphthalene have been investigated. As previously shown for other amines, this uptake was found to be a prerequisite for their acting as uncouplers. The technique provides a simple way to continuously follow changes in ApH in chloroplasts.A relation between energy generation and the quenching of the fluorescence of the uncoupler atebrin has been described by Kraayenhof [i]. He showed that the required energy could be provided by electron transport, ATP hydrolysis or a pH gradient and it was therefore suggested that the extent of quenching may be used to measure the "energy state" of the chloroplast [1,2]. A similar effect was described in chromatophores and was suggested to be related to proton movements, rather than to the "energy state" [3].We have recently shown that atebrin distributes between the inside of the chloroplast and the solution in accordance with the ratio of proton concentrations [4], in a manner similar to other amines [5,6]. The quenching was shown to be a consequence of its uptake and probably due to several factors [a]. Thus, as was shown with 5,5-dimethyl-2,4-oxazolidinadione in mitochondria [7] or methylamine [5,8] and NH, [9] in chloroplasts this uptake could be used as a measure of the H+ gradient across the membrane. Thus, an amine of a high pK will be distributed across the membrane in accordance with the proton concentration gradient.I n the case of diamine,

Mitochondrial membrane potential, in situ, is an important indicator of mitochondrial function and dysfunction. Because of recent interest in the role of mitochondria in signaling, cell injury and cell death, there is a need for a convenient, sensitive and accurate method for the measurement of the mitochondrial membrane potential, Deltapsim, in situ, in a heterogeneous cell population. We have adapted a flow cytometry method for the quantitative measurement of DeltaPsim which utilizes the lipophilic, cationic, fluorescent probe 3,3'-dihexyloxacarbocyanine iodide (DiOC6(3)). We developed a new protocol in which cells are equilibrated with very low dye concentrations (<1 nM). Only under these condition, the cell fluorescence appears to be correlated with the magnitude of DeltaPsim, as evident from the sensitivity of the fluorescence to low concentrations of uncouplers, ionophores and inhibitors of the mitochondrial proton pumps. The magnitude of the plasma membrane potential, DeltaPsip, also affects cell fluorescence, and a procedure that corrects for this effect is outlined. This method offers a distinct advantage over existing methods for estimation of Deltapsim by flow cytometry.

SummaryExcessive production of mitochondrial reactive oxygen species (mROS) is strongly associated with mitochondrial and cellular oxidative damage, aging, and degenerative diseases. However, mROS also induces pathways of protection of mitochondria that slow aging, inhibit cell death, and increase lifespan. Recent studies show that the activation of the mitochondrial permeability transition pore (mPTP), which is triggered by mROS and mitochondrial calcium overloading, is enhanced in aged animals and humans and in aging‐related degenerative diseases. mPTP opening initiates further production and release of mROS that damage both mitochondrial and nuclear DNA, proteins, and phospholipids, and also releases matrix NAD that is hydrolyzed in the intermembrane space, thus contributing to the depletion of cellular NAD that accelerates aging. Oxidative damage to calcium transporters leads to calcium overload and more frequent opening of mPTP. Because aging enhances the opening of the mPTP and mPTP opening accelerates aging, we suggest that mPTP opening drives the progression of aging. Activation of the mPTP is regulated, directly and indirectly, not only by the mitochondrial protection pathways that are induced by mROS, but also by pro‐apoptotic signals that are induced by DNA damage. We suggest that the integration of these contrasting signals by the mPTP largely determines the rate of cell aging and the initiation of cell death, and thus animal lifespan. The suggestion that the control of mPTP activation is critical for the progression of aging can explain the conflicting and confusing evidence regarding the beneficial and deleterious effects of mROS on health and lifespan.

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The uptake and binding of the lipophilic cations ethidium+, tetraphenylphosphonium+ (TPP+), triphenylmethylphosphonium+ (TPMP+), and tetraphenylarsonium+ (TPA+) in rat liver mitochondria and submitochondrial particles were investigated. The effects of membrane potential, surface potentials and cation concentration on the uptake and binding were elucidated. The accumulation of these cations by mitochondria is described by an uptake and binding to the matrix face of the inner membrane in addition to the binding to the cytosolic face of the inner membrane. The apparent partition coefficients between the external medium and the cytosolic surface of the inner membrane (K'o) and the internal matrix volume and matrix face of the inner membrane (K'i) were determined and were utilized to estimate the membrane potential delta psi from the cation accumulation factor Rc according to the relation delta psi = RT/ZF ln [(RcVo - K'o)/(Vi + K'i)] where Vo and Vi are the volume of the external medium and the mitochondrial matrix, respectively, and Rc is the ratio of the cation content of the mitochondria and the medium. The values of delta psi estimated from this equation are in remarkably good agreement with those estimated from the distribution of 86Rb in the presence of valinomycin. The results are discussed in relation to studies in which the membrane potential in mitochondria and bacterial cells was estimated from the distribution of lipophilic cations.