Rhodamine 123 as a probe of transmembrane potential in isolated rat-liver mitochondria: spectral and metabolic properties

Microprobe analysis of Tc-MIBI in heart cells: calculation of mitochondrial membrane potential

Hexakis (2-methoxyisobutylisonitrile) technetium-99m (99mTc-MIBI) is a gamma-emitting radiopharmaceutical probe currently in clinical use to evaluate myocardial perfusion. Biochemical and cellular pharmacological studies have suggested that Tc-MIBI, a lipophilic cation, is sequestered in mitochondria in response to transmembrane potentials. To assess directly the subcellular distribution of the probe in heart tissue, cultured chick heart cells were analyzed by electron-probe X-ray microanalysis (EPXMA) following equilibration in micromolar concentrations of carrier-added 99Tc-MIBI, the ground-state radiopharmaceutical. Quantitation of the physiological elements Na, Ca, Mg, K, S, P, and Cl was correlated with exposure to increasing concentrations of 99Tc-MIBI. EPXMA signals indicated that 99Tc-MIBI was concentrated up to 1,000 times into mitochondria in a dose-dependent fashion based on measured Tc content in the mitochondria. Inner membrane potential (delta psi) of individual mitochondria was calculated as -117 mV using the Nernst equation. Concentrations of 99Tc-MIBI > 36 microM caused a significant efflux of K and Mg from the cell, as well as an increase in Cl in the mitochondria. Comparison of cell ultrastructure with conventional electron microscopy at extracellular 99Tc-MIBI concentrations of 36-72 microM showed no changes compared with control. 99Tc-MIBI allows valuable in situ investigation of cellular bioenergetics with EPXMA by quantitation of delta psi.

Studies on Hg(II)-induced H2O2 formation and oxidative stress in vivo and in vitro in rat kidney mitochondria

Studies were undertaken to investigate the principal actions underlying mercury-induced oxidative stress in the kidney. Mitochondria from kidneys of rats treated with HgCl2 (1.5 mg/kg i.p.) demonstrated a 2-fold increase in hydrogen peroxide (H2O2) formation for up to 6 hr following Hg(II) treatment using succinate as the electron transport chain substrate. No increase in H2O2 formation was observed when NAD-linked substrates (malate/glutamate) were used, suggesting that Hg(II) affects H2O2 formation principally at the ubiquinone-cytochrome b region of the mitochondrial respiratory chain in vivo. Together with increased H2O2 formation, mitochondrial glutathione (GSH) content was depleted by more than 50% following Hg(II) treatment, whereas formation of thiobarbiturate reactive substances (TBARS), indicative of mitochondrial lipid peroxidation, was increased by 68%. Studies in vivo revealed a significant concentration-related depolarization of the inner mitochondrial membrane following the addition of Hg(II) to mitochondria isolated from kidneys of untreated rats. This effect was accompanied by significantly increased H2O2 formation, GSH depletion and TBARS formation linked to both NADH dehydrogenase (rotenone-inhibited) and ubiquinone-cytochrome b (antimycin-inhibited) regions of the electron transport chain. Oxidation of pyridine nucleotides (NAD[P]H) was also observed in mitochondria incubated with Hg(II) in vitro. In further studies in vitro, the potential role of Ca2+ in Hg(II)-induced mitochondrial oxidative stress was investigated. Ca2+ alone (30-400 nmol/mg protein) produced no increase in H2O2 and only a slight increase in TBARS formation when incubated with kidney mitochondria isolated from untreated rats. However, Ca2+ significantly increased H2O2 and TBARS formation elicited by Hg(II) at the ubiquinone-cytochrome b region of the mitochondrial electron transport chain, whereas TBARS formation was decreased significantly when the Ca2+ uptake inhibitors, ruthenium red or [ethylenebis(oxyethylenenitrilo)]tetraacetic acid (EGTA), were included with Hg(II) in the reaction mixtures. These findings support the view that Hg(II) causes depolarization of the mitochondrial inner membrane with consequent increased H2O2 formation. These events, coupled with Hg(II)-mediated GSH depletion and pyridine nucleotide oxidation, create an oxidant stress condition characterized by increased susceptibility of mitochondrial membranes to iron-dependent lipid peroxidation (TBARS formation). Since increased H2O2 formation, GSH depletion and lipid peroxidation were also observed in vivo following Hg(II) treatment, these events may underlie oxidative tissue damage caused by mercury compounds. Moreover, Hg(II)-induced alterations in mitochondrial Ca2+ homeostasis may exacerbate Hg(II)-induced oxidative stress in kidney cells.

Effect of hyperthermia on rhodamine 123 cytotoxicity in doxorubicin-sensitive and doxorubicin-resistant human breast carcinoma cell lines in vitro

Rhodamine 123 (Rh123) cytotoxicity and intracellular accumulation were studied in normothermic and hyperthermic conditions in a human breast carcinoma cell line (MCF7/WT) and its doxorubicin-resistant subline (MCF7/DoxR). MCF7/DoxR cells were resistant to hyperthermia and Rh123. Hyperthermic potentiation of Rh123 cytotoxicity was present in MCF7/WT but not in MCF7/DoxR cells. Results suggest that the effect observed in MCF7/WT cells is related to a heat-induced increased accumulation of Rh123 and not to a heat-induced activation of the drug. A low basal uptake and a fast release of Rh123 could explain the resistance of MCF7/DoxR to the drug. Resistance to Rh123 and lack of a heat-induced increased uptake account for the lack of hyperthermic enhancement of Rh123 cytotoxicity in the resistant cells.

Photoinactivation of the bovine heart mitochondrial F1-ATPase by [14C]dequalinium cross-links phenylalanine-403 or phenylalanine-406 of an alpha subunit to a site or sites contained within residues 440-459 of a beta subunit

Synthesis of [14C]dequalinium, 1,1'-(1,10-[1,10-14C]decanediyl)bis[4-amino-2-methylquinolinium ], is described, which photoinactivates the bovine heart mitochondrial F1-ATPase (MF1). Maximal photoinactivation occurs on incorporation of about 1.5 mol of [14C]dequalinium/mol of MF1. Three radioactive species were resolved when photoinactivated enzyme was submitted to polyacrylamide gel electrophoresis at pH 4.0 in the presence of tetradecyltrimethylammonium bromide, which correspond to the alpha and beta subunits and a cross-linked species with an M(r) of 116,000. Fractionation of a tryptic digest of photoinactivated enzyme by high-performance liquid chromatography led to isolation of a radioactive peptide which contains residues 399-420 of a alpha subunit. Two fragments containing equal amounts of radioactivity were obtained on fractionation of an endoproteinase Asp-N digest of the isolated radioactive tryptic peptide by high-performance liquid chromatography. Amino acid sequence analysis showed that both fragments contained residues 399-408 of the alpha subunit, but one was missing Phe-alpha 403 and the other was lacking Phe-alpha 406. Fractionation of a cyanogen bromide digest of photoinactivated enzyme followed by trypsin digestion of partially purified cyanogen bromide fragments and fractionation of the resulting radioactive tryptic fragments yielded several radioactive species comprised of residues 399-420 of the alpha subunit cross-linked to residues 440-459 of the beta subunit and a radioactive fragment containing residues 399-420 of the alpha subunit. Partial sequence analyses of the cross-linked fragments suggest that Phe-alpha 403 and Phe-alpha 406 participate in cross-links, whereas no information was obtained on the site or sites of cross-linking in the beta subunit fragment.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticosterone impairs hippocampal neuronal calcium regulation--possible mediating mechanisms

Corticosterone (CORT), the predominant glucocorticoid of rats which is secreted during stress, increases hippocampal neuronal vulnerability to excitotoxins, hypoxia-ischemia, and hypoglycemia in an energy-dependent manner. A mechanism for this endangerment could be the CORT-induced impairment of hippocampal neuronal calcium regulation. We have shown that CORT causes an energy-dependent prolonged elevation of cytosolic free calcium ([Ca2+]i) in response to kainic acid stimulation in cultured hippocampal neurons. That study utilized the calcium-sensitive dye fluo-3, which is unsuitable for determination of basal [Ca2+]i. The present study circumvents that limitation by using the dye fura-2 AM. We have replicated the previous demonstration that CORT potentiates the [Ca2+]i response to KA; we have also observed that CORT elevates basal [Ca2+]i concentrations. Furthermore, we have observed that the mechanism for this CORT impairment of calcium regulation involves a reduction in stimulus-induced calcium efflux. Energy-dependent disruptions in neuronal calcium regulation, such as induced by CORT, have been associated with subsequent neurotoxicity. Thus, the CORT-induced impairment of hippocampal neuronal calcium regulation could be the mechanism for the neuronal vulnerability and toxicity evident following CORT treatment and stress.

Mitochondrial dynamics in differentiating fiber cells of the mammalian lens

The distribution of mitochondria was investigated in living rat and monkey lenses using rhodamine 123 staining and confocal microscopy. In both species, epithelial cells contained abundant small mitochondria scattered throughout the cell volume. Mid-sagittal slices of the living monkey lens revealed that, at the lens equator, mitochondria were only present in fiber cells to a depth of approximately 100 microns. Mitochondria were not present in fiber cells that had already reached the suture line or fibers abutting the central epithelium. Dual-staining with rhodamine 123 and the vital nuclear stain thiazole orange revealed that the loss of nuclei and mitochondria was coincident during fiber cell differentiation.

Effects of rhodamine 123 in the dark and after irradiation on mitochondrial energy metabolism

Isolated rat liver mitochondria have been used to study the mechanism of toxicity of Rhodamine 123 (Rho 123) in the dark and after irradiation with visible light. We report an inhibition of adenosine 5'-diphosphate phosphorylation which is increased after illumination. In the dark, the first steps of the phosphorylation process (i.e. the entry of substrates into the matrix, the electron transport to oxygen and the creation of the proton gradient) as well as ATPase activity are not significantly perturbed at Rho 123 concentration below 10 micrograms/mL. In contrast, the movements of the phosphate compounds are drastically impaired. Irradiation strengthens the detrimental effects in an oxygen dependent process. The nature of the noxious transient species is not clearly established, but it is suggested that singlet oxygen could be responsible for the observed damage.

Functional sites in F1-ATPases: location and interactions

This review focuses on the location and interaction of three functional sites in F1-ATPases. These are catalytic sites which are located in beta subunits, noncatalytic nucleotide-binding sites which are located at interfaces of alpha and beta subunits and modulate the hydrolytic activity of the enzyme, and a site that binds inhibitory amphipathic cations which is at an interface of alpha and beta subunits. The latter site may participate in transmission of conformational signals between catalytic sites in F1 and the proton-conducting apparatus of F0 in the intact ATP synthases.

A novel cytotoxicity screening assay using a multiwell fluorescence scanner

A new assay using a multiwell fluorescence scanner was developed for screening cytotoxicity to cells cultured in 96-well microtiter plates. The assay is based on binding of propidium iodide to nuclei of cells whose plasma membranes have become permeable due to cell death. Fluorescence of propidium iodide measured with a multiwell fluorescence scanner increased in proportion to the number of permeabilized cells. After ATP depletion of hepatocytes and neonatal cardiac myocytes with metabolic inhibitors ("chemical hypoxia"), and exposure of Madine Darby canine kidney cells to the toxic chemical, HgCl2, propidium iodide fluorescence progressively increased. Increases of fluorescence were linearly proportional with release of lactate dehydrogenase into the culture medium. Employing this cytotoxicity screening assay, protection by various agents against lethal injury was evaluated in cultured hepatocytes during chemical hypoxia. Inhibitors of cysteine proteases (i.e., antipain, leupeptin, E-64), serine proteases (i.e., PMSF), and aspartic acid proteases (i.e., pepstatin A) did not protect against chemical hypoxia. In contrast, 1,10-phenanthroline, an inhibitor of metalloprotease, markedly protected against the onset of cell death during chemical hypoxia. Half-maximal protection after 60 min occurred at 0.5 microM. Phospholipase inhibitors, chlorpromazine (50 microM) and mepacrine (50 microM), also substantially retarded cell killing. U74006F, an inhibitor of lipid peroxidation, slowed cell killing to a lesser extent during chemical hypoxia and after oxidative stress with t-butyl hydroperoxide. Calciphor, a dimer of prostaglandin B1, did not protect against cell killing during chemical hypoxia or t-butyl hydroperoxide toxicity. In conclusion, this high capacity cytotoxicity assay for cells cultured in 96-well microtiter plates is suitable for rapid screening of potential cytoprotective agents in a variety of cell types.

Coincident loss of mitochondria and nuclei during lens fiber cell differentiation

During normal differentiation, lens fiber cells lose their nuclei, mitochondria, and other membrane-bound organelles. In the present study, a slice preparation of the embryonic chicken lens was used with laser scanning confocal microscopy to study the spatial and temporal patterns of organelle breakdown during embryonic development. At all stages examined, mitochondria in lens epithelial cells were present in perinuclear clusters. In contrast, early in development, lens fiber cells contained extremely elongated mitochondria (> 100 microns) that were distributed throughout the cytoplasm and oriented along the long axis of the cells. By the 8th day of embryonic development (E8), the mitochondria in the central fiber cells began to fragment. At the same time, the nuclei in these cells became smaller and more spherical. By E10, mitochondrial staining in the central fibers became punctate. Electron microscopy of this region revealed swollen mitochondria with disrupted cristae. By E12, cells in the central region of the lens lacked mitochondria and nuclei. The loss of nuclei and mitochondria from a given cell was coincident and abrupt (2-4 hr), occurring in a previously unsuspected domain situated about 300 microns from the anterior surface of the lens. A cytoskeletal component, actin, persisted in the central cells indicating that organelle degradation represents a selective process and not simply the global degradation of supramolecular structures. Throughout embryonic development, the organelle-free region grew at approximately the same rate as the lens and, by the time of hatching, had expanded to match the diameter of the pupil.(ABSTRACT TRUNCATED AT 250 WORDS)

Relative mitochondrial membrane potential and [Ca2+]i in type I cells isolated from the rabbit carotid body

1. In the accompanying paper (Duchen & Biscoe, 1992) we have described graded changes in autofluorescence derived from mitochondrial NAD(P)H in type I cells of the carotid body in response to changes of PO2 over a physiologically significant range. These observations suggest that mitochondrial function in these cells is unusually sensitive to oxygen and could play a role in oxygen sensing. We have now explored further the relationships between hypoxia, mitochondrial membrane potential (delta psi m) and [Ca2+]i. 2. The fluorescence of Rhodamine 123 (Rh 123) accumulated within mitochondria is quenched by delta psi m. Mitochondrial depolarization thus increases the fluorescence signal. Blockade of electron transport (CN-, anoxia, rotenone) and uncoupling agents (e.g. carbonyl cyanide p-trifluoromethoxy-phenylhydrazone; FCCP) increased fluorescence by up to 80-120%, while fluorescence was reduced by blockade of the F0 proton channel of the mitochondrial ATP synthase complex (oligomycin). 3. delta psi m depolarized rapidly with anoxia, and was usually completely dissipated within 1-2 min. The depolarization of delta psi m with anoxia (or CN-) and repolarization on reoxygenation both followed a time course well characterized as the sum of two exponential processes. Oligomycin (0.2-2 micrograms/ml) hyperpolarized delta psi m and abolished the slower components of both the depolarization with anoxia and of the subsequent repolarization. These data (i) illustrate the role of the F1-F0 ATP synthetase in slowing the rate of dissipation of delta psi m on cessation of electron transport, (ii) confirm blockade of the ATP synthetase by oligomycin at these concentrations, and (iii) indicate significant accumulation of intramitochondrial ADP during 1-2 min of anoxia. 4. Depolarization of delta psi m was graded with graded changes in PO2 below about 60 mmHg. The stimulus-response curves thus constructed strongly resemble those for [Ca2+]i and NAD(P)H with PO2. The change in delta psi m closely followed changes in PO2 with time. 5. The rate of rise of [Ca2+]i in response to anoxia is strongly temperature sensitive. The rate of depolarization of delta psi m with anoxia similarly increased at least two- to fivefold on warming from 22 to 36 degrees C. The change with FCCP was not significantly altered by temperature. 6. These data show that the mitochondrial membrane potential changes over a physiological range of PO2 values in type I cells. This contrasts with the behaviour in dissociated chromaffin cells and sensory neurons, in which no change was measurable until the PO2 fell close to zero.(ABSTRACT TRUNCATED AT 400 WORDS)

Mitochondrial function in type I cells isolated from rabbit arterial chemoreceptors

1. In this, and the accompanying paper (Duchen & Biscoe, 1992), we test the hypothesis that the oxygen sensitivity of mitochondrial electron transport forms a basis for transduction in the carotid body, the primary peripheral arterial oxygen sensor. We here describe for isolated type I cells the changes in autofluorescence of mitochondrial NAD(P)H that accompany changes in PO2. 2. NAD(P)H autofluorescence (excitation, 340-360 nm; emission peak, 450 nm) increased with anoxia, reflecting a rise in the NAD(P)H/NAD(P) ratio. Graded increases in autofluorescence were seen in response to graded decreases in PO2, suggesting that mitochondrial function is progressively altered below a PO2 of about 60 mmHg. 3. A mitochondrial origin for the NAD(P)H autofluorescence was suggested by the mutual exclusion of the responses to anoxia and cyanide. 4. Oxidized flavoproteins fluoresce when excited at 450 nm with an emission peak at 550 nm. The small signals obtained under these conditions increased with uncoupler and showed a graded decrease with falling PO2 reflecting a rise in the FADH/FAD ratio. 5. Hypoxia raises [Ca2+]i. The hypoxia-induced changes in mitochondrial function were not secondary to this rise. A brief K(+)-induced depolarization leads to a transient increase in [Ca2+]i. At the same time there is a rapid decrease in NAD(P)H autofluorescence followed by an increase that far outlasts the rise in [Ca2+]i. This delayed increase in autofluorescence was smaller than was the increase with anoxia, even though K(+)-induced depolarization raised [Ca2+]i more than does anoxia. In Ca(2+)-free solutions the depolarization-induced changes were abolished, while those associated with hypoxia were maintained. 6. The changes of autofluorescence with K(+)-induced depolarization appear to reflect (i) oxidation of NAD(P)H by stimulation of respiration following mitochondrial Ca2+ uptake and (ii) reduction of NAD(P) by the Ca(2+)-dependent activation of mitochondrial dehydrogenases. This activation could last several minutes following only 100 ms depolarization, while the changes accompanying hypoxia closely followed the time course of the change in PO2. 7. In similarly isolated rat or mouse chromaffin cells and mouse dorsal root ganglion neurons under identical conditions, no measurable change in autofluorescence or in [Ca2+]i was seen until the PO2 fell below about 5 mmHg. 8. Carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP) increases O2 consumption, oxidizing mitochondrial NADH and hence decreasing autofluorescence, (delta FFCCP). Blockade of electron transport by anoxia or CN- decreases O2 consumption, increasing mitochondrial NADH/NAD and autofluorescence (delta FCN). The fractional change in autofluorescence with FCCP, delta FFCCP/delta FFCCP+FCN), is thus a measure of resting O2 consumption.(ABSTRACT TRUNCATED AT 400 WORDS)

Ca(2+)-dependent changes in the mitochondrial energetics in single dissociated mouse sensory neurons

Depolarization of neurons promotes Ca2+ influx through voltage-activated channels, raising the intracellular Ca2+ concentration ([Ca2+]i). The consequences of such changes in [Ca2+]i for mitochondrial function were assessed in single, freshly dissociated mammalian neurons. Microfluorimetric techniques were used to measure [Ca2+]i, mitochondrial membrane potential [delta psi m, Rhodamine 123 (Rh 123) fluorescence], NAD(P)H/NAD(P)+ autofluorescence and flavoprotein autofluorescence combined with whole-cell voltage-clamp techniques. Brief (100-500 ms) depolarization of the cell membrane by high K+ or by voltage commands raised [Ca2+]i and depolarized delta psi m. The change in delta psi m was dependent on extracellular Ca2+. Under voltage-clamp control of the cell membrane, the voltage-dependence of the change in Rh 123 fluorescence reflected that of the Ca2+ current. The response was reduced by Ca2+ buffers introduced into the cell. The behaviour of this signal is thus consistent with a mitochondrial response to raised [Ca2+]i and does not reflect the change in cell membrane potential per se. Similar stimuli caused a rapid decrease of NAD(P)H autofluorescence, followed by an increase which could last several minutes. Flavoprotein fluorescence increased transiently, followed by a decrease lasting for several minutes. These signals indicate an initial oxidation of NAD(P)H and FADH, followed by a prolonged increase in the reduced state of both coenzymes. All these changes were dependent on extracellular [Ca2+]. Raising [Ca2+]i again during the period of NAD+ reduction caused an oxidizing response. Ruthenium Red applied to the cells (i) reduced both the Ca2+ current and the depolarization-induced [Ca2+]i transient and (ii) directly quenched Rh 123 fluorescence. When introduced into the cells with patch pipettes, it prevented the changes in autofluorescence without interfering with the Ca2+ conductance. Oligomycin blocked neither the response of delta psi m nor of NADH autofluorescence, suggesting that the signals do not reflect a response to falling ATP/ADP.Pi ratios as a consequence of the high [Ca2+]i. The changes in NADH autofluorescence were sustained in the presence of iodoacetic acid with pyruvate as substrate. Thus brief physiological elevations of [Ca2+]i depolarize delta psi m, probably through Ca2+ cycling across the mitochondrial inner membrane. The changes in autofluorescence are consistent with (i) increased respiration which could result from the depolarization of delta psi m, followed rapidly by (ii) increased activity of the Ca(2+)-dependent intramitochondrial enzymes. Changes in [Ca2+]i within a physiological range may thus promote significant and long-lasting changes in mitochondrial energy production.

A test of the singlet oxygen mechanism of cationic dye photosensitization of mitochondrial damage

Aromatic cationic dyes have a potential as photo-chemotherapeutic agents because they are selectively concentrated into the mitochondria of cancerous cells. The mechanism of cytophototoxicity has been proposed to be primarily due to dye sensitized photogeneration of highly toxic singlet oxygen (1O2) at the mitochondria. We tested this hypothesis by measuring the relative phototoxicity of a collection of aromatic cationic dyes towards respiring rat-liver mitochondria (RLM), upon addition of 514 nm laser light. Effectiveness of dye photosensitization towards destruction of RLM function was assayed by its effect on the RLM membrane potential. Three physical parameters of dye phototoxicity were independently measured and a relative phototoxicity calculated assuming adherence of mechanism to the 1O2 hypothesis. Quantum yields of dye sensitized 1O2 production were estimated, either from time-resolved luminescence measurements of photosensitized 1O2 formed, or by comparing rates of photobleaching of 1O2 trap; the relative partition of dye into mitochondrial lipid was determined gravimetrically; and the optical density of dye was determined in a lipid like Triton X-100 micellar environment. Under the assumption of the 1O2 hypothesis, these parameters were used to predict a relative phototoxicity which was compared with that observed. For 12 of the 14 dyes investigated, the observed and predicted phototoxicities were linearly correlated (r = 0.85) suggesting support of the 1O2 hypothesis. Carbocyanines DiOC2(3) and DiSC2(3) did not correlate and were found to be 10 and 1000 times more potent than predicted, suggesting an additional factor at play in their phototoxicity.

Trypanosoma (Nannomonas) congolense: changes in respiratory metabolism during the life cycle

All four life cycle stages (bloodstream, procyclic, epimastigote, and metacyclic) of Trypanosoma congolense IL 3000 were assayed with an oxygen electrode (polarograph) for the presence of terminal oxidases and carbon-source preference. In addition, these stages were used for histochemical analysis of mitochondrial activity using rhodamine 123, nitroblue tetrazolium, and diaminobenzidine. Morphometry was used to compare mitochondrial volumes and surface area among the different life cycle stages. It was found that in contrast to epimastigote forms, which were metabolically almost identical to procyclic forms, metacyclic forms showed characteristics of, and seemed preadapted to, differentiation into the bloodstream stage. While mitochondrial NAD+ diaphorase activity and an electrochemical potential were detected in all life cycle stages, metacyclic metabolism was glucose-based and terminal oxidase activity was primarily dependent upon the trypanosome alternative oxidase with the contribution of cyanide-sensitive respiration accounting for only 20-30% of the total respiratory capacity.

Disruption of the potential across the synaptosomal plasma membrane and mitochondria by neurotoxic agents

The effect of a neurotoxic organo-metal, methyl mercuric iodide, and an aromatic solvent, toluene, upon the transmembrane potential (psi), across both the limiting membrane of isolated nerve terminals and their mitochondria, has been studied. Exposure of nerve endings to either of these toxicants in vitro resulted in a dose-dependent diminution of psi that was especially pronounced in the case of mitochondria. This was not prevented by a concurrent exposure to an antioxidant (alpha-tocopherol), or an iron chelator (deferoxamine), or ganglioside GM1. No significant changes were detected in synaptosomal potentials derived from cortices of rats exposed to methyl mercury or toluene at levels known to increase the rate of formation of reactive oxygen species within this region. The special vulnerability of mitochondrial psi to these agents may be due to the disruption of oxidative phosphorylation and may be related to the increase in intrasynaptosomal free ionic calcium that both of these chemicals can induce.

Inhibitory effects of two structurally related carbocyanine laser dyes on the activity of bovine heart mitochondrial and Paracoccus denitrificans NADH-ubiquinone reductase. Evidence for a rotenone-type mechanism

Two cationic, lipophilic laser dyes, 1,1',3,3,3',3'-hexamethylindodicarbocyanine iodide (HIDC) and 1,1',3,3,3',3'-hexamethylindotricarbocyanine iodide (HITC), inhibit bovine heart mitochondrial and Paracoccus denitrificans NADH oxidase activities. The mitochondrial I50 values were 0.5 microM (HIDC) and 1.2 microM (HITC), and the P. denitrificans I50 values 1.2 microM (HIDC) and 1.5 microM (HITC). Neither succinate nor cytochrome oxidase (EC 1.9.3.1) activities were inhibited significantly by either compound, localizing the site of inhibition to the segment of each electron transport chain between NADH and ubiquinone. With submitochrondrial particles (SMP), NADH-dependent reduction of menadione, duroquinone and coenzyme Q1 was inhibited markedly (HIDC was the more potent inhibitor). Using purified complex I, only NADH-dependent reduction of duroquinone and coenzyme Q1 was inhibited markedly (HIDC was the more potent inhibitor) and reduction of menadione was inhibited slightly. With P. denitrificans membrane vesicles, NADH-dependent reduction of menadione, juglone, and coenzyme Q1 was inhibited slightly and duroquinone reduction was inhibited markedly. Membrane-dependent interactions appear to be involved, since the compounds were more inhibitory with membrane preparations than with complex I. The mechanism of inhibition (except for the HIDC effect on coenzyme Q1 reduction with P. denitrificans) appeared to be through the interaction of dye with the rotenone site on NADH-ubiquinone reductase (EC 1.6.99.3), since rotenone-insensitive preparations of complex I and P. denitrificans membrane vesicles were also insensitive to HIDC and HITC inhibition.

Autoradiography of progesterone and model compound entry and distribution in Xenopus laevis oocytes

Xenopus laevis oocytes resume meiosis in response to progesterone. The initial interaction involves surface binding to numerous low-affinity receptor proteins. The mechanism of entry and functions of intracellular steroid are unknown. Because the latter are important for understanding progesterone-induced maturation, a dry-mount autoradiographic technique for analyzing entry and intracellular distribution of radiolabeled steroids was developed and tested. The distinguishing feature of this cryo-technique is sample preparation directly in incubation media using uncross-linked polyacrylamide for inert support. The external ligand functions as an internal standard, so quantitation is by simple ratio (bound/free). The entry kinetics and subcellular binding patterns in large oocytes were studied using this method at nM levels of radiolabeled steroids and model compounds. Progesterone, estradiol, corticosterone, and 1,25-dihydroxycholecalciferol all showed rapid entry (P approximately 10(-6) cm/sec). Entry rates were not saturable with unlabeled steroid. Intracellular patterns of these steroids were highly specific and negatively associated with yolk protein and lipid. Intracellular binding in animal hemisphere ooplasm was 10x that of the yolk-rich vegetative ooplasm. In contrast, dexamethasone, ponasterone-A, and ecdysone displayed entry rates 20-60x slower than progesterone with little compartmentalization. Glycerol, glucose, and leucine entered over 10x slower than progesterone. Cholesterol and Ca++ had entry rates below detection. Evidence for mediated entry of progesterone included the rapid saturation of a cortical compartment equivalent in magnitude to reported receptor numbers. The kinetics and specificity of cortical uptake were consistent with low-affinity, high capacity protein binding. Intracellular binding was seen to correlate with rhodamine 123 patterns, suggesting involvement of mitochondrial or other microtubule-associated structures in steroid responses. Mitochondrial binding is consistent with the limited steroid metabolism seen in oocytes. Since several maturation events are consistent with respiratory uncoupling, reported by others for steroids and isolated organelles, and since mitochondria contain nearly all of the oocyte DNA, a role for these organelles in steroid-induced oocyte maturation was proposed.

Analysis of the membrane potential of rat- and mouse-liver mitochondria by flow cytometry and possible applications

Washed and purified rat- or mouse-liver mitochondria exhibiting high membrane integrity and metabolic activity were studied by flow cytometry. The electrophoretic accumulation/redistribution of cationic lipophilic probes, rhodamine 123, safranine O and a cyanine derivative, 3,3'-dihexyloxadicarbocyanine iodide, during the energization process was studied and was consistent with the generation of a negative internal membrane potential. An exception to this was nonylacridine orange which spontaneously bound to the mitochondrial membrane by hydrophobic interactions via its hydrocarbon chain. Energized purified mitochondria stained with potentiometric dyes exhibited both higher fluorescence and population homogeneity than the non-energized or deenergized (nigericin plus valinomycin) mitochondria. By contrast, under non-energized or deenergized conditions, the mitochondrial population exhibited fluorescence intensity heterogeneity related to the residual membrane potential; two subpopulations were evident, one of low fluorescence which may be related to the autofluorescence of the mitochondria (plus non-specific dye binding) and a second population which exhibited high fluorescence. Flow cytometry of the unpurified, simply washed, rat-liver mitochondria stained with rhodamine 123, a classically used dye, provided evidence of their heterogeneity in terms of light-scattering properties and membrane-potential-related fluorescence. One third of the washed mitochondria were found to be non-functional by such assays. The fluorescence of purified rat-liver mitochondria due to the membrane potential built up by endogenous substrates indicates heterogeneity of the mitochondrial population with respect to levels of endogenous substrates. The low-angle light scattering increases upon energization and provides some original information about the shape and modification of the inner mitochondrial conformation accompanying the energization. The heterogeneity of the rat liver mitochondrial population, from a structural, metabolic (existence of endogenous substrates) and functional (active and non-active mitochondrial population dispersion) point of view could thus be demonstrated by flow-cytometry analysis. Two animal models were examined with regard to the alteration of the mitochondrial membrane potential under the effects of drugs (rat-liver mitochondria), and the effects of ammonium toxicity (mouse-liver mitochondria). These results are promising and open new perspectives in the study of mitochondriopathies.

Uptake and retention of hexakis (2-methoxyisobutyl isonitrile) technetium(I) in cultured chick myocardial cells. Mitochondrial and plasma membrane potential dependence

The fundamental myocellular uptake and retention mechanisms of hexakis (2-methoxyisobutyl isonitrile) technetium(I) (Tc-MIBI), a technetium-99m-based myocardial perfusion imaging agent, are unresolved. Because of the lipophilic cationic nature of Tc-MIBI, it may be distributed across biological membranes in response to transmembrane potential. To test this hypothesis, net uptake and retention of Tc-MIBI in cultured chick embryo ventricular myocytes were determined under conditions known to alter mitochondrial and plasma membrane potentials. Isovolumic depolarization of plasma membrane potentials in 130 mM extracellular K (Ko) 20 mM extracellular Cl buffer reduced net accumulation of Tc-MIBI from 171 +/- 16 (control) to 29 +/- 3.3 fmol intracellular Tc-MIBI/mg protein.nM extracellular Tc-MIBI. Unidirectional influx of Tc-MIBI in cells depolarized in 30 mM Ko buffer was also reduced; a resting plasma membrane potential of -87 +/- 6 mV was calculated from the Goldman flux equation using normal Ko/high Ko Tc-MIBI influx ratios. Addition of the potassium ionophore valinomycin to cells incubated in 130 mM Ko buffer to additionally depolarize mitochondrial membrane potentials further reduced net uptake of Tc-MIBI to levels comparable to that found in nonviable freeze-thawed preparations ([Tc-MIBI]i/[Tc-MIBI]o = 1). By depolarizing mitochondrial (and in part plasma membrane) potentials with the protonophores 2,4-dinitrophenol and carbonyl cyanide m-chlorophenylhydrazone (CCCP) Tc-MIBI was rapidly depleted from 181 +/- 16 (control) to 16 +/- 2.6 and 31 +/- 4.2 fmol/mg protein.nMo, respectively, with kinetics that did not correlate with loss of cellular ATP content. CCCP alone inhibited 90 +/- 3% of net accumulation or 66 +/- 3% of unidirectional influx of Tc-MIBI in a concentration-dependent manner. By hyperpolarizing mitochondrial membrane potentials with the K+/H+ ionophore nigericin or the ATP synthase inhibitor oligomycin, net uptake and retention of Tc-MIBI were increased by 60 +/- 9% and 375 +/- 20%, respectively. Caffeine, as well as the respiratory chain electron transport inhibitor rotenone, did not significantly alter net cell uptake (p greater than 0.2). These data indicate that the fundamental myocellular uptake mechanism of Tc-MIBI involves passive distribution across plasma and mitochondrial membranes and that at equilibrium Tc-MIBI is sequestered within mitochondria by the large negative transmembrane potentials.

Relationships between the mitochondrial transmembrane potential, ATP concentration, and cytotoxicity in isolated rat hepatocytes

The relationships between mitochondrial transmembrane potential, ATP concentration, and cytotoxicity were evaluated after exposure of isolated rat hepatocytes to different mitochondrial poisons. Both the neurotoxicant 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its fully oxidized metabolite, the 1-methyl-4-phenylpyridinium (MPP+) ion, caused a concentration- and time-dependent depolarization of mitochondrial membranes which followed ATP depletion and preceded cytotoxicity. The effect of MPTP, but not that of MPP+, was prevented by deprenyl, an inhibitor of MPTP conversion to MPP+ via monoamine oxidase type B. Addition of fructose to the hepatocyte incubations treated with either MPTP or MPP+ counteracted the loss of mitochondrial transmembrane potential. Fructose was also effective in protecting against the mitochondrial membrane depolarization as well as ATP depletion and cytotoxicity induced by antimycin. A, carbonyl cyanide p-trifluoromethoxyphenyl hydrazone, and valinomycin. Data confirm the key role played by MPP(+)-induced mitochondrial damage in MPTP toxicity and indicate that (i) ATP produced via the glycolytic pathway can be utilized by hepatocytes to maintain mitochondrial electrochemical gradient, and (ii) a loss of mitochondrial membrane potential may occur only when supplies of ATP are depleted.

Effect of local anaesthetics on mitochondrial membrane potential in living cells

Using the laser dye rhodamine 123, we demonstrated that local anaesthetics can reach mitochondria in cell culture and reversibly decrease, or even collapse, their transmembrane potential. This effect is highly dependent on the lipid-solubility of the local anaesthetic and can be facilitated by the presence of a lipophilic anion.

Assessment of Fura-2 for measurements of cytosolic free calcium

Fura-2 has become the most popular fluorescent probe with which to monitor dynamic changes in cytosolic free calcium in intact living cells. In this paper, we describe many of the currently recognized limitations to the use of Fura-2 in living cells and certain approaches which can circumvent some of these problems. Many of these problems are cell type specific, and include: (a) incomplete hydrolysis of Fura-2 acetoxymethyl ester bonds by cytosolic esterases, and the potential presence of either esterase resistant methyl ester complexes on the Fura-2/AM molecule or other as yet unidentified contaminants in commercial preparations of Fura-2/AM; (b) sequestration of Fura-2 in non-cytoplasmic compartments (i.e. cytoplasmic organelles); (c) dye loss (either active or passive) from labeled cells; (d) quenching of Fura-2 fluorescence by heavy metals; (e) photobleaching and photochemical formation of fluorescent non-Ca2+ sensitive Fura-2 species; (f) shifts in the absorption and emission spectra, as well as the Kd for Ca2+ of Fura-2 as a function of either polarity, viscosity, ionic strength or temperature of the probe environment; and (g) accurate calibration of the Fura-2 signal inside cells. Solutions to these problems include: (a) labeling of cells with Fura-2 pentapotassium salt (by scrape loading, microinjection or ATP permeabilization) to circumvent the problems of ester hydrolysis; (b) labeling of cells at low temperatures or after a 4 degrees C pre-chill to prevent intracellular organelle sequestration; (c) performance of experiments at lower than physiological temperatures (i.e. 15-33 degrees C) and use of ratio quantitation to remedy inaccuracies caused by dye leakage; (d) addition of N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) to chelate heavy metals; (e) use of low levels of excitation energy and high sensitivity detectors to minimize photobleaching or formation of fluorescent non-Ca2+ sensitive forms of Fura-2; and (f) the use of 340 nm and 365 nm (instead of 340 nm and 380 nm) for ratio imaging, which diminishes the potential contributions of artifacts of polarity, viscosity and ionic strength on calculated calcium concentrations, provides a measure of dye leakage from the cells, rate of Fura-2 photobleaching, and can be used to perform in situ calibration of Fura-2 fluorescence in intact cells; however, use of this wavelength pair diminishes the dynamic range of the ratio and thus makes it more sensitive to noise involved in photon detection. Failure to consider these potential problems may result in erroneous estimates of cytosolic free calcium.(ABSTRACT TRUNCATED AT 400 WORDS)

Specific interaction of the new fluorescent dye 10-N-nonyl acridine orange with inner mitochondrial membrane. A lipid-mediated inhibition of oxidative phosphorylation

The fluorescent dye 10-N-nonyl acridine orange (NAO), known as specifically associated with mitochondria, has been reported to have a cytotoxic effect when high doses were applied to cells. Presently, the biochemical basis of its toxicity was investigated on isolated rat liver mitochondria. At low concentrations, NAO strongly inhibited state 3 respiration and ATP synthesis. At high concentrations, electron transport, ATP hydrolysis, Pi-transport and adenine nucleotide activities were also decreased. All these inhibitions can be explained by probe-cardiolipin interactions which could induce the collapse of energy conversion and/or the modification of membrane fluidity.

Use of nonyl acridine orange and rhodamine 123 to follow biosynthesis and functional assembly of mitochondrial membrane during L1210 cell cycle

Specific mitochondrial incorporation of 10 N-nonyl acridine orange (NAO) is demonstrated by subcellular fractionation of rat hepatocytes. Moreover, comparative studies with NAO and rhodamine 123 (Rh 123) prove that acridine orange-derivative uptake is independent of transmembrane mitochondrial potential, a property allowing its utilization for the assessment of mitochondrial membrane mass modifications under various physiological states. Using NAO and Rh 123, we have respectively followed the biosynthesis of mitochondrial membrane and its assembly under a functional state during the L1210 cell cycle. Their evolution occurs in two stages according to a well-defined sequential order. Mitochondrial biogenesis, as revealed by NAO incorporation, occurs essentially in the G1 phase (probably mitochondrion enlargement) but also starts in late S phase (probably mitochondrion division). The increased amount of functional mitochondrial membrane, monitored by Rh 123 uptake, is emphasized in late G1 (prerequisite to DNA synthesis) and during G2M phases (prerequisite to mitosis). This alternative succession of phases displays the existence of a time-lag between the biosynthesis of mitochondrial membrane and its functional organization. Such an analysis confirms the potential of the NAO probe to evaluate mitochondrial membrane mass changes in various biological fields.

Bioregulatory mechanisms at the level of cell organelle interactions: microspectrofluorometric in situ studies

The spatiotemporal analysis of bioregulatory mechanisms at the level of intracellular multienzyme complexes and organelle interactions is made possible by the availability of endogenous and exogenous fluorescence probes, the development of microspectrofluorometers allowing one- and two-dimensional scans of intracellular fluorescence reactions, and the use of micromanipulatory techniques enabling the rapid alteration of metabolic states. Absorbed photons are not only a tool for quantitative evaluation of metabolic processes, they can also trigger alterations of cell membranes and functions as mediated by photosensitizer drugs. In the hierarchy of intracellular organization different levels of complexity are accessible to study, such as the regulation of multienzyme complexes and the interaction of organelle complexes. Typical applications of these methods are the investigation of drug effects (e.g., on melanoma cells), metabolic and structural alterations (e.g., in cystic fibrosis and Gaucher fibroblasts), organelle interactions in cells treated with toxic agents. The implications are relevant to biotechnology for better control of metabolite production and processing, design and testing of new drugs, understanding of drug resistance and better targeting of drugs or probes to selected intracellular sites. In addition, such in vitro methods can contribute to the provision of an alternative to "whole animal experiments" as already achieved in human and mouse fibroblasts, hepatocytes, hepatoma, Swiss 3T3 cells and other cells in culture, especially with regards to an analysis of the action of xenobiotics and drugs in cell physiology and pathology, fluorescence recovery after photobleaching, study of cytoskeleton dynamics and multiparameter probing of organelle activity during in vitro wound repair.

Simultaneous analysis of mitochondrial activity and DNA content in Ehrlich ascites tumor cells by dual parameter flow cytometry

Ehrlich ascites tumor cells were permeabilized using low concentrations of digitonin, 8 micrograms/10(6) cells. Permeabilization was monitored by the assay of lactate dehydrogenase released into the incubation medium and of hexokinase partially bound to mitochondria. Integrity of the cellular organelles was unaffected as determined by assay of the mitochondrial enzyme glutamate dehydrogenase. Cells were stained with rhodamine 123 as a mitochondrial specific dye and propidium iodide/mithramycin as DNA specific dyes. The green fluorescence of bound rhodamine 123 versus red fluorescence of DNA in individual cells was analysed by dual parameter flow cytometry. Incubation of cells with inhibitors of mitochondrial energy metabolism, such as, potassium cyanide and carbonyl cyanide m-chlorophenylhydrazone abolished binding of rhodamine 123. Flow cytometric data allowed a correlation between cell position in the mitotic cycle with total mitochondrial activity. In addition, comparison of the characteristics of propidium iodide and ethidium bromide staining further elucidated the molecular basis of the staining with the positively-charged fluorescent dye rhodamine 123.

Simultaneous imaging of cell and mitochondrial membrane potentials

The distribution of charged membrane-permeable molecular probes between intracellular organelles, the cytoplasm, and the outside medium is governed by the relative membrane electrical potentials of these regions through coupled equilibria described by the Nernst equation. A series of highly fluorescent cationic dyes of low membrane binding and toxicity (Ehrenberg, B., V. Montana, M.-D. Wei, J. P. Wuskell, and L. M. Loew, 1988. Biophys. J. 53:785-794) allows the monitoring of these equilibria through digital imaging video microscopy. We employ this combination of technologies to assess, simultaneously, the membrane potentials of cells and of their organelles in situ. We describe the methodology and optimal conditions for such measurements, and apply the technique to concomitantly follow, with good time resolution, the mitochondrial and plasma membrane potentials in several cultured cell lines. The time course of variations induced by chemical agents (ionophores, uncouplers, electron transport, and energy transfer inhibitors) in either or both these potentials is easily quantitated, and in accordance with mechanistic expectations. The methodology should therefore be applicable to the study of more subtle and specific, biologically induced potential changes in cells.

Fluorescent cationic probes of mitochondria. Metrics and mechanism of interaction

Mitochondria strongly accumulate amphiphilic cations. We report here a study of the association of respiring rat liver mitochondria with several fluorescent cationic dyes from differing structural classes. Using gravimetric and fluorometric analysis of dye partition, we find that dyes and mitochondria interact in three ways: (a) uptake with fluorescence quenching, (b) uptake without change in fluorescence intensity, and (c) lack of uptake. For dyes that quench upon uptake, the extent of quenching correlates with the degree of aggregation of the dye to dimers, as predicted by theory (Tomov, T.C. 1986. J. Biochem. Biophys. Methods. 13:29-38). Also predicted is the relationship observed between quenching and the mitochondria concentration when constant dye is titrated with mitochondria. Not predicted is the relationship observed between quenching and dye concentration when constant mitochondria are titrated with dye. Because a limit to dye uptake exists, in this case, the degree of quenching decreases as dye is added. A Langmuir isotherm analysis gives phenomenological parameters that predict quenching when it is observed as a function of dye concentration. By allowing for a decrease in membrane potential, caused by incorporation of cationic dye into the lipid bilayer, a modification of the Tomov theory predicts the dye titration data. We present a model of cationic dye-mitochondria interaction and discuss the use of these as probes of mitochondrial membrane potential.

10-N nonyl-acridine orange: a fluorescent probe which stains mitochondria independently of their energetic state

The specificity of binding of 10-N Nonyl Acridine Orange to mitochondria, and more precisely to inner membranes, is demonstrated by subcellular fractionation of hepatocytes. Unlike Rhodamine 123, which is a preferential marker of the transmembrane potential, Nonyl Acridine Orange binding is essentially independent of the mitochondria energization state although a low uptake of this dye, in response to the potential, may be measured. So 10-N Nonyl acridine orange is an appropriate marker of the mitochondial membrane surface per unit of cell mass.

Inhibition of the bovine-heart mitochondrial F1-ATPase by cationic dyes and amphipathic peptides

The bovine heart mitochondrial F1-ATPase is inhibited by a number of amphiphilic cations. The order of effectiveness of non-peptidyl inhibitors examined as assessed by the concentration estimated to produce 50% inhibition (I0.5) of the enzyme at pH 8.0 is: dequalinium (8 microM), rhodamine 6G (10 microM), malachite green (14 microM), rosaniline (15 microM) greater than acridine orange (180 microM) greater than rhodamine 123 (270 microM) greater than rhodamine B (475 microM), coriphosphine (480 microM) greater than safranin O (1140 microM) greater than pyronin Y (1650 microM) greater than Nile blue A (greater than 2000 microM). The ATPase activity was also inhibited by the following cationic, amphiphilic peptides: the bee venom peptide, melittin; a synthetic peptide corresponding to the presence of yeast cytochrome oxidase subunit IV (WT), and amphiphilic, synthetic peptides which have been shown (Roise, D., Franziska, T., Horvath, S.J., Tomich, J.M., Richards, J.H., Allison, D.S. and Schatz, G. (1988) EMBO J. 7, 649-653) to function in mitochondrial import when attached to dihydrofolate reductase (delta 11.12, Syn-A2, and Syn-C). The order of effectiveness of the peptide inhibitors as assessed by I0.5 values is: Syn-A2 (40 nM), Syn-C (54 nM) greater than melittin (5 microM) greater than WT (16 microM) greater than delta 11,12 (29 microM). Rhodamines B and 123, dequalinium, melittin, and Syn-A2 showed noncompetitive inhibition, whereas each of the other inhibitors examined (rhodamine 6G, rosaniline, malachite green, coriphosphine, acridine orange, and-Syn-C) showed mixed inhibition. Replots of slopes and intercepts from Lineweaver-Burk plots obtained for dequalinium were hyperbolic indicating partial inhibition. With the exception of Syn-C, for which the slope replot was hyperbolic and the intercept replot was parabolic, steady-state kinetic analyses indicated that inhibition by the other inhibitors was complete. The inhibition constants obtained by steady-state kinetic analyses were in agreement with the I0.5 values estimated for each inhibitor examined. Rhodamine 6G, rosaniline, dequalinium, melittin, Syn-A2, and Syn-C were observed to protect F1 against inactivation by the aziridinium of quinacrine mustard in accord with their experimentally determined I0.5 values.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparative developmental toxicity of cationic and neutral rhodamines in mice

Rhodamines 123 and 6G (Rh 123 and Rh 6G) are cationic fluorescent dyes that inhibit oxidative phosphorylation following their selective accumulation within mitochondria. Neutral rhodamines (e.g., Rh 116 and Rh B) do not share these properties. To determine if cationic and neutral rhodamines differ in their effect on mammalian development, pregnant CD-1 mice were injected i.p. with Rh 123, Rh B, or Rh 116 at doses of 15 mg/kg/day. The rhodamines were given alone or in combination with 500 mg/kg/day 2-deoxy-D-glucose (2-DOG), an inhibitor of glycolysis, daily on gestation days 7-10 (copulation plug = day 1). Additional pregnant mice were similarly treated with Rh 6G at a dose of 0.5 mg/kg/day. Controls were given saline equimolar to the dose of 2-DOG. Treatment with Rh 6G, alone or in combination with 2-DOG, significantly increased the incidences of prenatal mortality (17% and 35%, respectively) when compared with the control incidence (6%). Treatment with Rh 123 or Rh 6G, alone or with 2-DOG, inhibited fetal growth. Treatment with the neutral rhodamines had little effect on prenatal survival or growth. Exposure to Rh 6G, with or without 2-DOG, was associated with high incidences of gross malformations (41% and 61%, respectively). Rh 116 or Rh B, with or without 2-DOG, and Rh 123 alone were not associated with statistically significant teratogenic effects, but results of the latter treatment were suggestive of such an effect (9.1% grossly malformed fetuses vs. 0% for controls). The incidences of skeletal malformations were significantly increased in the test groups given Rh 6G + 2-DOG, Rh 123 + 2-DOG, or Rh 6G alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Photosensitization of human glioma cells by chalcogenapyrylium dyes

Chalcogenapyrylium (CP) dyes which are specifically activated by red and near infrared light (600-900 nm) were examined as potential photosensitizers for photochemotherapy of malignant gliomas. Eleven CP dyes of varying chemical structure and redox potential were evaluated for selective toxicity against glioma and normal skin fibroblast cell cultures both before and after light activation. Eight of eleven CP dyes exhibited differential toxicity to tumor over fibroblast cells at dye concentrations of 1.0 microM. Dose dependent toxicity was seen both in the dark and after laser light activation. The toxicity of two of the CP dyes was significantly enhanced by photoactivation with 800 nm light. The CP dyes that absorb light maximally between 775 and 850 nm, in the range of excellent light penetration through brain, appear to be promising candidates as photosensitizers for treating malignant brain tumors.

Inhibition of mitochondrial respiration by cationic rhodamines as a possible teratogenicity mechanism

Exposure of mice to cationic rhodamines, Rh 123 and Rh 6G, has been found to be associated with developmental toxicity, while neutral rhodamines (e.g., Rh B) had no such effect. When mouse embryos from dams given ip injections of Rh 123, Rh 6G (15 mg/kg), or Rh B (30 mg/kg) on gestation Day (GD) 10 were examined, Rh 123, Rh 6G were present in embryonic tissue in fluorescent bodies within the average dimensions of mitochondria. Rh B was evenly distributed in the cytoplasm. With in vitro exposure of isolated mitochondria to rhodamines on GD 12, 3-4 times more Rh 123 was associated with mitochondria under energized conditions than under nonenergized conditions; the amount of Rh 6G associated with mitochondria was much less under either condition. Treatment of pregnant mice (ip) with Rh 123 (15 mg/kg/day) or Rh 6G (0.5 mg/kg/day) on GD 7-10 resulted in inhibition of state 3 respiration of embryonic mitochondria isolated on GD 12. When isolated embryonic mitochondria were exposed to the cationic rhodamines, inhibition of state 3 respiration was dose dependent. With 5 micrograms of Rh 123/mg mitochondrial protein, state 3 respiration decreased by 31%, while Rh 6G (1 microgram/mg) decreased state 3 respiration by 27%. In vivo exposure of maternal liver mitochondria to cationic rhodamines did not result in inhibition of respiration 2 days later, whereas in vitro results were similar to those for embryonic mitochondria. In vivo or in vitro exposure to Rh B had no effects on mitochondrial respiration. These results indicate that interference with embryonic energy metabolism is a possible mechanism by which cationic rhodamines exert adverse effects on embryogenesis.

The effect of a chalcogenapyrylium dye with and without photolysis on mitochondrial function in normal and tumor cells

A chalcogenapyrylium dye 8b, which is under investigation for the photodynamic therapy of malignant gliomas (brain tumors), was evaluated for inhibition of mitochondrial function both before and after exposure to laser light of 800 nm. Neoplastic and normal cells forced to use mitochondrial substrates were killed by the light-activation of intracellular 8b as well as exposure to classic mitochondrial inhibitors, rotenone and sodium azide. Correspondingly, cells in glucose-rich media showed little decrease in viability due to the photolysis of intracellular 8b or the presence of mitochondrial toxins. The toxicity of 8b without light activation was found to be the same regardless of the cell's energy source. Measurement of cellular ATP generated during treatment also showed the photolysis of intracellular 8b to be more inhibitory towards mitochondrial function than the unactivated parent compound. We conclude that the chalcogenapyrylium dyes localize to the mitochondrion and that photoactivation results in mitochondrial injury.

Effects of in vivo and in vitro exposure to rhodamine dyes on mitochondrial function of mouse embryos

Cationic rhodamines (Rh 123 and Rh 6G) can cause developmental toxicity in mice and inhibit embryonic mitochondrial respiration following in vivo or in vitro dye exposure. Rh B, a neutral rhodamine, fails to show such effects at comparable doses. To assess effects of rhodamines on development, F0F1ATPase activity and ADP translocation were measured on gestation day (GD) 12 in embryonic and adult mitochondria. ATP synthesis in embryonic mitochondria transplacentally exposed to Rh 123 (15 mg/kg/day) or Rh 6G (0.5 mg/kg/day) given to dams by i.p. injection from GD 7 to 10 were inhibited 39% and 49%, respectively. When isolated mitochondria were treated, dose-dependent inhibition was seen; at 5 micrograms of dye/mg mitochondrial protein, ATP synthesis was inhibited 65% and 81% by Rh 123 and Rh 6G, respectively. When F0F1ATPase activity was assessed, in vitro Rh 123 and Rh 6G exposures at levels up to 8 micrograms/mg mitochondrial protein resulted in enzyme inhibition, but at 10 micrograms/mg, ATPase activity was stimulated. Uncoupler-stimulated ATPase activity was also inhibited. ADP translocation was decreased by 19.1% and 37.7% by Rh 123 and Rh 6G, respectively, at dye concentrations of 20 micrograms/mg. Results of in vitro exposure of maternal liver mitochondria were similar to those for embryonic mitochondria, whereas liver from dams exposed in vivo on GD 7-10 was unaffected on GD 12. In vivo or in vitro treatment with Rh B did not affect any embryonic or maternal parameters. Such results support the hypothesis that inhibition of mitochondrial energy metabolism is a mechanism for the developmental toxicity of cationic rhodamines.

Inhibition and photoinactivation of the bovine heart mitochondrial F1-ATPase by the cytotoxic agent, dequalinium

The bovine heart mitochondrial F1-ATPase is inhibited in the dark by the amphipathic cation, dequalinium, with a I0.5 of about 12 microM at pH 7.5. When illuminated at 350 nm in the presence of 1.7 microM dequalinium, the F1-ATPase is inactivated with a pseudo-first order rate constant of 7.9 X 10(-3) min-1. The apparent Kd of the dequalinium-enzyme complex was estimated to be about 12.5 microM by examining the rate of inactivation of the ATPase with 1.7-16.7 microM dequalinium. ATP, ADP, Pi, and Mg2+, singly or in combination, protected the ATPase against photoinactivation, with Mg2+ plus Pi being the most effective.

The activity of powdery-mildew haustoria after feeding the host cells with different sugars, as measured with a potentiometric cyanine dye

The biotrophic parasite Erysiphe graminis f. sp. hordei produces haustoria within the cells of its host Hordeum vulgare. To determine the physiological activity of these haustoria, the electric potential across the membranes in the mitochondria of the haustorium was studied. The membrane potential was estimated with the fluorescent potentiometric cyanine dye 3,3'-dibutyloxacarbocyanine iodide. The addition of depolarizing agents (carbonylcyanide m-chlorophenylhydrazone, 2,4-dinitrophenol or KCN) to infected cells resulted in an increase of fluorescence after the addition of low concentrations or a decrease of fluorescence after the addition of higher concentrations. When the infected host cell was fed with increasing concentrations of D-glucose (25, 50, 75 mM), corresponding decreases of fluorescence were measured immediately in the mitochondria of the fungal haustoria. Sucrose induced a similar reduction of fluorescence about 20 min late. D-Galactose and D-fructose induced a somewhat smaller reduction of fluorescence, L-glucose and D-glucitol had no effect. The results indicate that haustoria take up glucose from the host cells immediately. Sucrose, D-galactose and D-fructose seem to require time to be metabolized before their products reach the fungal haustorium or mitochondria.

The hydrophobic cationic cyanine dye inhibits oxidative phosphorylation by inhibiting ADP transport, not by electrophoretic transfer, into mitochondria

The effect of the divalent cationic cyanine dye tri-S-C4(5) on oxidative phosphorylation in rat liver mitochondria was examined. The dye at about 100 n mols per mg mitochondrial protein inhibited state 3 respiration and ATP synthesis almost completely. However, it had no effect on submitochondrial particles, like other hydrophobic cations. The dye inhibited the transport of ADP into mitochondria mediated by the adenine nucleotide translocator. Thus, the inhibition of oxidative phosphorylation by the cationic dye was concluded to be due to its action on the adenine nucleotide translocator, not to its electrophoretic transfer into the inner space of mitochondria according to the inside-negative electrochemical potential.