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

Response of isolated rat liver mitochondria to variation of external osmolarity in KCl medium: regulation of matrix volume and oxidative phosphorylation

When isolated rat liver mitochondria are incubated in KCI medium, matrix volume, flux, and forces in both hypo- and hyperosmolarity are time-dependent. In hypoosmotic KCl medium, matrix volume is regulated via the K+/H+ exchanger. In hyperosmotic medium, the volume is regulated in such a manner that at steady state, which is reached within 4 min, it is maintained whatever the hyperosmolarity. This regulation is Pi- and deltamuH+-dependent, indicating Pi-K salt entry into the matrix. Under steady state, hyperosmolarity has no effect on isolated rat liver mitochondria energetic parameters such as respiratory rate, proton electrochemical potential difference, and oxidative phosphorylation yield. Hypoosmolarity decreases the NADH/NAD+ ratio, state 3 respiratory rate, and deltamuH+, while oxidative phosphorylation yield is not significantly modified. This indicates kinetic control upstream the respiratory chain. This study points out the key role of potassium on the regulation of matrix volume, flux, and forces. Indeed, while matrix volume is regulated in NaCl hyperosmotic medium, flux and force restoration in hyperosmotic medium occurs only in the presence of external potassium.

Hypoxia-induced catecholamine secretion in isolated newborn rat adrenal chromaffin cells is mimicked by inhibition of mitochondrial respiration

1. In newborn mammals, systemic hypoxia provokes catecholamine secretion from the adrenal medulla. In contrast to adults, this release is independent of sympathetic innervation. We have studied the cellular processes involved in hypoxia-induced catecholamine secretion, employing fluorimetric techniques to measure changes in [Ca2+]i, NADH and mitochondrial potential, and voltammetric techniques to record changes in PO2 and catecholamine secretion. 2. In adrenal chromaffin cells freshly dissociated from newborn rats, severe hypoxia increased [Ca2+]i and secretion of catecholamines, indicating that the response of the newborn adrenal medulla to hypoxia is an intrinsic property of these cells. Discrete quantal secretory events were identifiable, suggesting an exocytotic mechanism of secretion. 3. Hypoxia-induced secretion was only seen when PO2 fell below 5 mmHg, similar to the threshold arterial PO2 reported to stimulate release in vivo. Such oxygen tensions also inhibited mitochondrial metabolism, shown by an increase in NADH autofluorescence. We therefore explored the involvement of mitochondria in oxygen sensing. Inhibition of mitochondrial respiration either by CN- at complex IV or by rotenone at complex I mimicked severe hypoxia, reversibly increasing both [Ca2+]i and catecholamine secretion. The CN(-)-induced depolarization of the mitochondrial inner membrane potential preceded the increase in [Ca2+]i by approximately 6 s. 4. The effects of severe hypoxia and CN- on [Ca2+]i and catecholamine secretion were not additive, suggesting a common mechanism. 5. Chemical anoxia failed to increase [Ca2+]i in a significant proportion of cells dissociated from 2- to 4-week-old rats. Thus, the sensitivity to hypoxia is specific to adrenal chromaffin cells dissociated from newborn rats. 6. These data indicate that hypoxia-induced catecholamine secretion in the newborn adrenal medulla is mediated by reversible inhibition of mitochondrial respiration, leading to an increase in [Ca2+]i and catecholamine secretion.

On the mechanism of rebounding of calcium in liver mitochondria

Rat liver mitochondria are able to temporarily lower the steady state concentration of external Ca2+ after having accumulated a pulse of added Ca2+. This could be due to inhibition of efflux or/and stimulation of influx of Ca2+. This question has been addressed in mitochondria respiring on succinate +/- malonate. In the presence of malonate the depression of the membrane potential during Ca2+ uptake is more extensive and the rate of Ca2+ uptake slower. There were no discernible differences in the rates of efflux either after inhibition of the calcium uniporter by Ruthenium Red or by studying efflux of preloaded 45Ca-labeled Ca2+. The efflux was not changed by diltiazem or cyclosporin A to inhibit Ca2+ exchange on the Ca2+/nNA+ antiporter or efflux through the permeability transition pore. It is concluded that the rebounding is due mainly to stimulation of the calcium uniporter.

Recording of mitochondrial transmembrane potential and volume in cultured rat osteoclasts by confocal laser scanning microscopy

Osteoclasts are multinuclear bone-resorbing cells which contain abundant mitochondria. Morphological studies have suggested that a correlation may exist between mitochondrial concentration and bone resorption by osteoclasts. However, investigation of mitochondrial transmembrane potential (delta psi) and volume has been hampered by the difficulty in obtaining a sufficient number of osteoclasts for assessing these characteristics by flow cytometric analysis. In this study, we have used confocal laser scanning microscopy after loading the cells with Rhodamine 123 and 10-nonyl Acridine Orange to record mitochondrial delta psi and volume, respectively, in isolated rat osteoclasts cultured on bovine bone slices. Optimal staining conditions were found to be 10 micrograms ml-1 for 40 min for Rhodamine, and 1 microM for 10 min for the 10-nonyl Acridine Orange derivative. Two osteoclast populations, whose shape seemed to reflect bone resorption and migratory functions, were identified depending on their shape and on the distribution of the two dye probes. 'Round-shaped' osteoclasts had significantly higher mitochondrial delta psi and volume in the apical regions than in the basolateral portions (p < 0.00001). In contrast, mitochondrial delta psi and volume in 'irregular-shaped' osteoclasts were rather evenly distributed in both these regions (p > 0.05). Our results indicate that there is an apical polarization of mitochondria in osteoclasts corresponding to the energy demands associated with bone resorption.

Synaptic physiology and mitochondrial function in crayfish tonic and phasic motor neurons

Phasic and tonic motor neurons of crustaceans differ strikingly in their junctional synaptic physiology. Tonic neurons generally produce small excitatory postsynaptic potentials (EPSPs) that facilitate strongly as stimulation frequency is increased, and normally show no synaptic depression. In contrast, phasic neurons produce relatively large EPSPs with weak frequency facilitation and pronounced depression. We addressed the hypothesis that mitochondrial function is an important determinant of the features of synaptic transmission in these neurons. Mitochondrial fluorescence was measured with confocal microscopy in phasic and tonic axons and terminals of abdominal and leg muscles after exposure to supravital mitochondrial fluorochromes, rhodamine-123 (Rh123) and 4-diethylaminostyryl-N-methylpyridinium iodide (4-Di-2-Asp). Mitochondria of tonic axons and neuromuscular junctions had significantly higher mean Rh123 and 4-Di-2-Asp fluorescence than in phasic neurons, indicating more accumulation of the fluorochromes. Mitochondrial membrane potential, which is responsible for Rh123 uptake and is related to mitochondrial oxidative activity (the production of ATP by oxidation of metabolic substrates), is likely higher in tonic axons. Electron microscopy showed that tonic axons contain approximately fivefold more mitochondria per microm2 cross-sectional area than phasic axons. Neuromuscular junctions of tonic axons also have a much higher mitochondrial content than those of phasic axons. We tested the hypothesis that synaptic fatigue resistance is dependent on mitochondrial function in crayfish motor axons. Impairment of mitochondrial function by uncouplers of oxidative phosphorylation, dinitrophenol or carbonyl cyanide m-chlorophenylhydrazone, or by the electron transport inhibitor sodium azide, led to marked synaptic depression of a tonic axon and accelerated depression of a phasic axon during maintained stimulation. Iodoacetate, an inhibitor of glycolysis, and chloramphenicol, a mitochondrial protein synthesis inhibitor, had no significant effects on either mitochondrial fluorescence or synaptic depression in tonic or phasic axons. Collectively, the results provide evidence that mitochondrial oxidative metabolism is important for sustaining synaptic transmission during maintained stimulation of tonic and phasic motor neurons. Tonic neurons have a higher mitochondrial content and greater oxidative activity; these features are correlated with their greater resistance to synaptic depression. Conversely, phasic neurons have a lower mitochondrial content, less oxidative activity, and greater synaptic fatigability.

Formation of pH and potential gradients by the reconstituted Azotobacter vinelandii cytochrome bd respiratory protection oxidase

To directly characterize the bioenergetic properties of the cytochrome bd terminating branch of the Azotobacter vinelandii electron transport chain, the purified cytochrome bd oxidase was reconstituted into a phospholipid environment consisting of phosphatidylethanolamine and phosphatidylglycerol (3:1). The average diameter of the proteoliposomes after extrusion through a polycarbonate membrane was 94 +/- 4 nm. Initiation of respiration upon the addition of 20 microM ubiquinone-1 to proteoliposomes loaded with the pH-sensitive dye pyranine resulted in an immediate alkalization of the vesicle lumen by an average pH change of 0.11 unit. This pH gradient was readily collapsed upon the addition of nigericin, carbonyl cyanide p-(tri-fluoromethoxy) phenyl-hydrazone, gramicidin, Triton X-100, or 2-heptyl-4-hydroxyquinoline N-oxide (HQNO). Proteoliposomal respiration initiated in the presence of the potentiometric membrane dye rhodamine 123 caused the generation of a transmembrane potential; the potential was collapsed upon the addition of either valinomycin or HQNO. The formation of both pH and potential gradients during turnover demonstrates that the A. vinelandii cytochrome bd oxidase is coupled to energy conservation in vivo.

The absence of the mitochondrial ATP synthase delta subunit promotes a slow growth phenotype of rho- yeast cells by a lack of assembly of the catalytic sector F1

In the yeast Saccharomyces cerevisiae, inactivation of the gene encoding the delta subunit of the ATP synthase led to a lack of assembly of the catalytic sector. In addition a slow-growth phenotype was observed on fermentable medium. This alteration appears in strains lacking intact mitochondrial DNA and showing a defect in the assembly of the catalytic sector, such as the yeast strain inactivated in the gene encoding the epsilon subunit. In rho mitochondria having an intact F1, the ion movement resulting from the exchange of ADP formed in the organelle and ATP entering the mitochondrial compartment led to a mitochondrial transmembranous potential delta psi that was sensitive to carboxyactractyloside. This ion movement was dramatically decreased in rho mitochondria lacking the delta subunit and thus the F1 sector, whereas a cell devoid of delta subunit and complemented with a plasmid harboring the ATPdelta gene displayed an assembled F1, a normal generation time and a fully restored mitochondrial potential. This result could be linked to the involvement of the membrane potential delta psi which is indispensible for mitochondrial biogenesis.

Rhodamine 123 accumulates extensively in the isolated perfused rat kidney and is secreted by the organic cation system

Rhodamine 123 has been shown to be a substrate for P-glycoprotein in multidrug resistant cells. In the present investigation the disposition of rhodamine 123 was studied in the isolated perfused rat kidney. After exposing the kidneys to perfusate concentrations ranging from 10 to 1000 ng/ml, the renal clearance was 4-1 times the clearance by glomerular filtration, respectively, indicating active and saturable secretion of rhodamine 123. The rate-limiting step in secretion was found to be membrane passage from cell to tubular lumen. Suprisingly, renal clearance was not influenced by the P-glycoprotein inhibitors cyclosporin A or digoxin. However, pretreatment of the kidneys with verapamil and quinidine (inhibitors of both P-glycoprotein and organic cation transport) or cimetidine (organic cation transport inhibitor) resulted in a significantly reduced rhodamine 123 clearance, indicating that the renal organic cation carrier may be involved in active secretion. Rhodamine 123 accumulated extensively in the isolated perfused rat kidney; tissue concentrations of 270-360 times the perfusate concentration were determined. Similar accumulation ratios at different perfusate concentrations were found, suggesting that the compound enters the tubular cells by (facilitated) diffusion. In conclusion, rhodamine 123 accumulated extensively in the isolated perfused rat kidney and active renal secretion appears to be preferentially mediated by the organic cation carrier and not by P-glycoprotein.

Cobalt and desferrioxamine reveal crucial members of the oxygen sensing pathway in HepG2 cells

Cobalt and desferrioxamine, like hypoxia, stimulate the production of erythropoietin in HepG2 cells. It is believed that cobalt as well as desferrioxamine interact with the central iron atom of heme proteins by changing their redox state similar to hypoxia. A subsequent decrease of the intracellular H2O2 levels under hypoxia was presumed to be the key event for stimulating erythropoietin production. We therefore investigated whether cobalt and desferrioxamine control the intracellular H2O2 levels that regulate gene expression by interacting with hemeproteins. Deconvolution of light absorption spectra revealed respiratory heme proteins such as cytochrome c, b558 and cytochrome aa3, as well as cytochrome b558, which is a nonrespiratory heme protein found in HepG2 cells. Whereas respiratory heme proteins are located in mitochondria, cytochrome b558 similar to the one described for the neutrophil NADPH oxidase can be visualized in the cell membrane of HepG2 cells by immunohistochemistry. Incubation with cobalt (100 microM/24 hr) interacts predominantly with cytochrome b558 and cytochrome b558. The interaction of cobalt with the respiratory chain results in an increased oxygen consumption of HepG2 cells as revealed by PO2 microelectrode measurements. Desferrioxamine (130 microM/24 hr), however has no influence on the cytochromes. In response to an external application of NADH (1 mM), the membrane bound cytochrome b558 produces two times more O2- than to the external NADPH (1 mM) application. Neither desferrioxamine not cobalt has any influence on the NADH stimulated O2- generation. Incubation with cobalt or with desferrioxamine, however, leads to a decrease of the intracellular H2O2 level as revealed by the dihydrorhodamine 123 technique, perhaps causing the well-known enhanced erythropoietin production. The cobalt-induced H2O2 decrease seems to be caused by an increased activity of the glutathion peroxidase that is also induced under hypoxia. Desferrioxamine, however, leads to an apparent H2O2 decrease only because it seems to inhibit the iron catalyzed reaction of H2O2 with dihydrorhodamine 123, hinting at the occurrence of the Fenton reaction in HepG2 cells. Therefore, it must be determined whether or not degradation products of H2O2 by the Fenton reaction suppress erythropoietin production under normoxia.

The hepatotoxicity of rhein involves impairment of mitochondrial functions

Metabolism of rhein (4,5-dihydroxyanthraquinone-2-carboxylic acid) in primary cultures of rat hepatocytes caused production of oxygen-derived free radicals by redox cycling; this was shown as an increased rate of superoxide-dismutasesensitive NAD(P)H oxidation and NAD(P)H-cytochrome c reduction. Furthermore, rhein caused a depletion of intracellular reduced glutathione and an immediate, almost 10-fold increase in intracellular free Ca2+. Exposure to rhein also induced the following: a decrease in the mitochondrial membrane potential, as analyzed by uptake of rhodamine 123 (Rh 123); initiation of lipid peroxidation, measured as accumulation of malondialdehyde and 4-hydroxyalkenals; and cell death (LD50 = 20 microM). Pretreatment of cell cultures with dithiothreitol (DTT), nifedipin or N',N'-diphenyl-p-phenylenediamine (DPPD) increased the intracellular free Ca2+ concentration 5-fold but inhibited rhein-induced cytotoxicity. Moreover, addition of these protecting substances maintained the level of ATP and glutathione (GSH) and prevented accumulation of lipid peroxidation products. Depletion of intracellular glutathione by pretreatment with buthionine sulfoximine (BSO), or inhibition of glutathione reductase with 1,3-bis-2-chloroethyl-1-nitrosourea (BCNU) decreased cell viability (LD50 = 2.5 microM). On the other hand, increasing GSH by pretreatment with L-2-oxothiazolidine-4-carboxylic acid (OTC) did not provide complete protection. In summary, rhein undergoes redox cycling that gives rise to oxygen metabolites that affect the mitochondrial membranes (recorded as a decreased membrane potential) and after the plasma membrane (i.e. induced the formation of surface blebs). Mitochondrial malfunction also causes changes in Ca2+ homeostasis and depletion of ATP, which eventually lead to cell death.

CD18/ICAM-1-dependent nitric oxide production of Kupffer cells as a cause of mitochondrial dysfunction in hepatoma cells: influence of chronic alcohol feeding

The present study was designed to monitor the process for hepatoma cell injury induced by Kupffer cells. The non-activated Kupffer cells isolated from male Wistar rats reduced the mitochondrial membrane potential in the cocultured AH70 cells, which was indicated by the decreased rhodamine 123 (Rh123) fluorescence. Increased level of nitrite and nitrate in the medium and induction of iNOS in Kupffer cells were observed after coculture with AH70 cells. Incubation with either NG-monomethyl-L-arginine or aminoguanidine attenuated the increased nitric oxide (NO) production of Kupffer cells and the decreased Rh123 fluorescence of AH70 cells. Fluo-3, a calcium-sensitive probe, fluorescence in Kupffer cells increased after coculture with AH70 cells. Addition of TMB-8, a calcium inhibitor, or monoclonal antibody directed against ICAM-1 or CD18 prevented the increases in fluo-3 fluorescence and NO production of Kupffer cells and Kupffer cell-induced mitochondrial dysfunction in AH70 cells, suggesting the involvement of calcium mobilization and CD18/ICAM-1. It is therefore suggested that the Kupffer cell-mediated mitochondrial dysfunction of hepatoma cells largely depends on NO production by iNOS, and that the NO production by Kupffer cells is triggered by CD18/ICAM-1-dependent interaction with hepatoma cells and subsequent calcium mobilization. In other series of experiments, male Wistar rats fed ethanol for 4 weeks were used. The NO production and calcium mobilization of Kupffer cells and reduction of the mitochondrial membrane potential in cocultured hepatoma cells were diminished in the case of Kupffer cells isolated from chronically ethanol-fed rats, while CD18 and ICAM-1 expression was still observed. Thus, the present study further suggests that NO-dependent anti-hepatoma cell activity of Kupffer cells is suppressed in chronically ethanol-fed animals.

Voltage-dependent translocation of R18 and DiI across lipid bilayers leads to fluorescence changes

We show that the lipophilic, cationic fluorescent dyes R18 and Dil translocate from one monolayer of a phospholipid bilayer membrane to the other in a concentration and voltage-dependent manner. When the probes were incorporated into voltage-clamped planar membranes and potentials were applied, displacement currents resulted. The charged probes sensed a large fraction of the applied field. When these probes were added to only one monolayer, displacement currents were symmetrical around 0 mV, indicating that the probes distributed equally between the two monolayers. Charge translocation required that the bilayer be fluid. When membranes were in a condensed gel phase, displacement currents were not observed; raising the temperature to above the gel-liquid crystalline transition restored the currents. Translocation of R18 was also shown by fluorescence measurements. When R18 was in the bilayer at high, self-quenching concentrations, voltage pulses led to voltage-dependent fluorescence changes. The kinetics of the fluorescence changes and charge translocations correlated. Adding the quencher I- to one aqueous phase caused fluorescence to decrease or increase when voltage moved R18 toward or away from the quencher at low, nonquenching concentrations of R18. In contrast to R18, Dil incorporated into bilayers was a carrier fo I-, and hence I- altered Dil currents. Voltage-driven translocations allow R18 and Dil to be used to probe membrane potential changes.

Sphingosine-induced inhibition of capacitative calcium influx in CFPAC-1 cells

Sphingosine (10 microM) induced mobilization of intracellular Ca2+ stores in the pancreatic duct adenocarcinoma cell line CFPAC-1. The effect was specific for sphingosine, since the sphingosine analog C2-ceramide had no effect. Sphingosine did not cause Ca2+ entry from extracellular medium, as also shown by following Mn2+ quenching of Fura-2 fluorescence. Furthermore, sphingosine, similarly to the mitochondrial inhibitors rotenone and oligomycin, strongly inhibited the rate of Mn2+ entry triggered by both thapsigargin- and agonist-induced depletion of intracellular stores. The uptake of rhodamine 123, a lipophilic cation which estimates mitochondrial energy level, was reduced by sphingosine to an extent similar to that observed in the presence of mitochondrial inhibitors. It is suggested that impairment of mitochondrial function might be responsible for inhibition of capacitative Ca2+ entry caused by sphingosine.

Dynamical change of mitochondrial DNA induced in the living cell by perturbing the electrochemical gradient

Digital-imaging microscopy was used in conditions that allowed the native state to be preserved and hence fluorescence variations of specific probes to be followed in the real time of living mammalian cells. Ethidium bromide was shown to enter into living cells and to intercalate stably into mitochondrial DNA (mtDNA), giving rise to high fluorescence. When the membrane potential or the pH gradient across the inner membrane was abolished by specific inhibitors or ionophores, the ethidium fluorescence disappeared from all mtDNA molecules within 2 min. After removal of the inhibitors or ionophores, ethidium fluorescence rapidly reappeared in mitochondria, together with the membrane potential. The fluorescence extinction did not result from an equilibrium shift caused by leakage of free ethidium out of mitochondria when the membrane potential was abolished but was most likely due to a dynamical mtDNA change that exposed intercalated ethidium to quencher, either by weakening the ethidium binding constant or by giving access of a proton acceptor (such as water) to the interior of mtDNA. Double labeling with ethidium and with a minor groove probe (4',6-diamino-2-phenylindole) indicated that mtDNA maintains a double-stranded structure. The two double-stranded DNA states, revealed by the fluorescence of mitochondrial ethidium, enhanced or quenched in the presence of ethidium, seem to coexist in mitochondria of unperturbed fibroblast cells, suggesting a spontaneous dynamical change of mtDNA molecules. Therefore, the ethidium fluorescence variation allows changes of DNA to be followed, a property that has to be taken into consideration when using this intercalator for in vivo as well as in vitro imaging studies.

A critical evaluation of in situ measurement of mitochondrial electrical potentials in single hepatocytes

The range of applicability and the critical parameters involved in the assessment of mitochondrial electrical potential (delta psi mit) using epifluorescence microscopy were evaluated based on both theoretical and experimental analysis. Rat hepatocytes loaded with the potential-dependent fluorescent dye rhodamine 123 exhibited the expected heterogeneity of fluorescence distribution with dark regions corresponding to the nucleus and bright regions corresponding to the mitochondria-rich cytosol. Calibration of the signal was performed by permeabilizing the cell membrane for monovalent cations using nystatin and gramicidin, and equilibrating the cell with a K(+)-free bath solution. A voltage-clamp at defined delta psi mit was then achieved after addition of valinomycin in the presence of different K+ concentrations in the bath. Theoretical analysis indicated that the ratio of fluorescence intensity measured in mitochondria-rich and mitochondria-poor regions of cell was related with delta psi mit and yielded quantitative estimates of electrical potential with an accuracy of 10-20 mV. The ratio tended to plateau at potentials more negative than-140 mV, showing a limitation of the technique. Manoeuvres such as imposing a heavy ATP demand or interfering with the mitochondrial respiration depolarized mitochondria, while delta psi mit was not altered in a measurable manner during Ca2+ oscillations consecutive to alpha 1-agonist stimulation.

Renal oxidant injury and oxidant response induced by mercury

The role of oxidative stress in mercuric chloride (HgCl2)-induced nephrotoxicity is uncertain and controversial. We demonstrate that I.L.C-PK1 cells, exposed to HgCl2, generate massive amounts of hydrogen peroxide, the latter completely quenched by the hydrogen peroxide scavenger, pyruvate. HgCl2 exerts a dose-dependent cytotoxicity which is attenuated by pyruvate and catalase. Cellular generation of hydrogen peroxide arises, at least in part, from mitochondria since mitochondrial rates of generation of hydrogen peroxide increase in response to HgCl2; HgCl2 also provokes a shift in absorbance spectra in rhodamine 123 loaded-mitochondria and stimulates mitochondrial state 4 respiration. HgCl2, applied for one hour, impairs cellular vitality as demonstrated by the MTT assay, an assay dependent in part on mitochondrial function. HgCl2 impairs function in other organelles such as lysosomes that maintain a transmembrane proton gradient; these latter effects are partially attenuated by pyruvate. We complement these in vitro findings with in vivo evidence demonstrating that HgCl2 stimulates renal generation of hydrogen peroxide. The functional significance of such generation of hydrogen peroxide was evaluated in rats deficient in selenium and vitamin E, a nutrient deficiency that impairs the scavenging of hydrogen peroxide and promotes the toxicity of this oxidant. In these rats serum creatinine values were significantly higher on sequential days following the administration of HgCl2. To probe the renal response to oxidative stress induced by HgCl2, we examined hydrogen peroxide-scavenging enzymes and redox-sensitive genes. Catalase activity was unaltered whereas glutathione peroxidase activity was decreased, effects that may contribute to the net renal generation of hydrogen peroxide. The redox sensitive enzyme, heme oxygenase, was markedly up-regulated in the kidney in response to HgCl2. HgCl2 also induced members of the bcl family, bcl2 and bclx, genes that protect against apoptosis and oxidant injury. In another model of oxidant-induced renal injury, the glycerol model, bcl2 mRNA was not induced at 6 and 24 hours after the administration of glycerol. In summary, we demonstrate that HgCl2 potently stimulates renal generation of hydrogen peroxide in vitro and in vivo and such generation of peroxide contributes to renal dysfunction in vitro and in vivo. We also demonstrate that in response to HgCl2, redox sensitive genes are expressed including heme oxygenase and members of the bcl family.

ATP synthase of yeast mitochondria. Isolation of the subunit h and disruption of the ATP14 gene

A new subunit of the yeast ATP synthase (termed subunit h) has been isolated. Amino acid composition and N-terminal sequencing were determined by chemical methods. These data were in agreement with the sequence of the hypothetical protein L8003.20 whose primary structure was deduced from DNA sequencing of the yeast chromosome XII. The amino acid sequence encoded by ATP14 gene is 32 amino acids longer than the mature protein, which contains 92 amino acids corresponding to a calculated mass of 10,408 Da. The protein is hydrophilic and acidic with a calculated pHi of 4.08. It is not apparently related to any subunit described in other ATP synthases. A null mutant was constructed. The mutation was recessive and the mutant strain was unable to grow on glycerol medium. A high percentage of rho- cells arose spontaneously. The mutant mitochondria had no detectable oligomycin-sensitive ATPase activity, but still contained ATPase activity with a catalytic sector dissociated from the membranous components. The mutant mitochondria did not contain subunit h, and the mitochondrially encoded hydrophobic subunit 6 was not present.

Energy metabolism of adult astrocytes in vitro

In this study we established cultures of astrocytes from the forebrain of the adult rat. The homeostatic regulatory mechanisms of the aerobic and anaerobic pathways of energy metabolism in these cells showed that adult astrocytes express many of the regulatory properties previously demonstrated in neonatal astrocytes. Changes in mitochondrial respiration and ATP production were readily evident upon incubation with the relevant substrates. Inhibition of mitochondrial respiration led to a compensatory increase in anaerobic glycolysis as evidenced by an increased release of lactate. We assessed the role of cytosolic calcium in the regulation of the mitochondrial energy metabolism. Increases in cytosolic calcium concentration in response to ATP or stimulation of mechanical receptors were followed by depolarizations of the mitochondrial membrane potential, whose magnitude reflected the amplitude of the cytosolic calcium response. The changes in mitochondrial membrane potential were largely dependent on the presence of external calcium. These results provide the first evidence of a signalling mechanism in astrocytes by which changes in cytosolic calcium mediate changes in respiration, possibly through mitochondrial calcium uptake and subsequent activation of several mitochondrial dehydrogenases. This signalling pathway would thus ensure that energy demands due to changes in cytosolic calcium concentrations are met by increases in energy production through increases in mitochondrial oxidative phosphorylation.

Slow fluorescent indicators of membrane potential: a survey of different approaches to probe response analysis

Basic tenets related to the use of three main classes of potentiometric redistribution fluorescent dyes (carbocyanines, oxonols, and rhodamines) are discussed in detail. They include the structure/function relationship, formation of nonfluorescent (H-type) and fluorescent (J-type) dimers and higher aggregates, probe partitioning between membranes and medium and binding to membranes and intracellular components (with attendant changes in absorption and emission spectra, fluorescence quantum yield and lifetime). The crucial importance of suitable probe-to-cell concentration ratio and selection of optimum monitored fluorescence wavelength is illustrated in schematic diagrams and possible artifacts or puzzling results stemming from faulty experimental protocol are pointed out. Special attention is paid to procedures used for probe-response calibration (potential clamping by potassium in the presence of valinomycin, use of gramicidin D in combination with N-methylglucamine, activation of Ca-dependent K-channels by A23187, the null-point technique). Among other problems treated are dye toxicity, interaction with mitochondria and other organelles, and possible effects of intracellular pH and the quantity of cytosolic proteins and/or RNA on probe response. Individual techniques using redistribution dyes (fluorescence measurements in cuvettes, flow cytometry and microfluorimetry of individual cells including fluorescence confocal microscopy) are discussed in terms of reliability, limitations and drawbacks, and selection of suitable probes. Up-to-date examples of application of slow dyes illustrate the broad range of problems in which these probes can be used.

Toxicity of dichloropropanols in rat hepatocyte cultues

Exposure of humans to dichloropropanols has been shown to result in fulminant hepatic necrosis. These compounds have also been shown to be hepatotoxic in rats. In this study, 1,3-dichloropropanol, but not 2,3-dichloropropanol, was shown to be toxic to 24 h cultures of rat hepatocytes. The toxicity was inhibited by pre-treatment of cultures with a cytochrome P450 inhibitor and enhanced by prior depletion of cellular glutathione. In addition, at equimolar concentrations both isomers were shown to deplete glutathione, although the extent of depletion was greater with the 1,3-isomer. 1,3-Dichloropropanol also depleted ATP and reduced the mitochondrial membrane potential. The effects on ATP, glutathione and membrane potential could be inhibited by the cytochrome P450 inhibitor. It is concluded that the toxicity of 1,3-dichloropropanol is mediated by cytochrome P450 and involves depletion of glutathione and loss of mitochondrial function.

Continuous monitoring of mitochondrial membrane potential in hepatocyte cell suspensions

We report a simple fluorometric method for the continuous monitoring of mitochondrial membrane potential and cell viability in suspensions of hepatocytes exposed in vitro to cytotoxic agents. Suspensions of freshly isolated hepatocytes (10(6) cells/mL) preloaded with rhodamine 123 (Rh 123, 100 mumol/L) are transferred to a thermostatically controlled mixed cuvette to which the desired cytotoxic agent is added. Rh 123 is a cationic fluorophore that is actively accumulated by cells in direct proportion to the mitochondrial membrane potential. Cell viability was estimated by monitoring propidium iodide (PI) fluorescence. Exposure of cell suspensions to the mitochondrial uncoupling agent FCCP caused an immediate and titratable increase in Rh 123 fluorescence. Subsequent treatment with digitonin did not change Rh 123 fluorescence, suggeseting that Rh 123 equilibrates rapidly across the intact cell membrane. Likewise, treatment of hepatocyte suspensions with inhibitors of mitochondrial respiration (rotenone, cyanide, or menadione) caused an immediate increase in Rh 123 fluorescence. This was accompanied by a progressive increase in PI fluorescence, suggesting a causal relationship between mitochondrial depolarization and cell injury. In contrast, 1,4-benzoquinone caused a time-dependent and linear increase in PI fluorescence that paralleled changes in Rh 123 fluorescence. Comparing the time courses for changes in PI and Rh 123 fluorescence suggests that for benzoquinone, the depolarization of the mitochondria is a consequence rather than a cause of the cell injury. This modified procedure provides a simple and specific technique for continuously monitoring mitochondrial membrane potential and cell viability in suspensions of freshly isolated hepatocytes. The advantage is that there is no need to separate cells from the incubation medium, making it possible to record real-time changes in mitochondrial membrane potential and cell viability throughout the in vitro exposure period.

Temporal correlation between maximum tetanic force and cell death in postischemic rat skeletal muscle

To gain insight into the mechanisms responsible for muscle dysfunction after ischemia-reperfusion, a rat spinotrapezius muscle preparation was developed which enabled sequential measurements of in vivo maximum tetanic force production and cell death assessed using digital microfluorographic determination of propidium iodide (PI) staining. After 60 min of no-flow ischemia, maximum tetanic force fell significantly during 90 min of reperfusion compared with control, nonischemic muscles. The most striking fall was evident within 30 min of reperfusion and occurred concomitant with an explosive increase in PI-positive myocyte nuclei. Treatment with the oxygen radical scavenger, dimethylthiourea, attenuated both the fall in force and increased PI staining. Indeed, the rise in PI-positive nuclei correlated closely (r= 0.728) with the reduction of maximum tetanic force developed following ischemia and reperfusion under all conditions. Superoxide dismutase also attenuated the rise in PI-positive nuclei. Assessment of mitochondrial inner membrane potential (deltapsi) using Rhodamine 123 fluorescence revealed that myocytes with the lowest initial mitochondrial membrane potential were subject to the greatest injury after 90 min of reperfusion (r= 0.828). These results support the hypothesis that myocyte injury, as visualized by PI-staining, reflects an impaired contractile function in fibers with a low oxidative potential which is likely mediated by oxygen radicals.

Changes in adult rat liver mitochondrial populations at different energy states analyzed by flow cytometry

The present work studies the changes in green fluorescence intensity after Rh-123 staining of the low (LFP) and the high fluorescence populations (HFP) in isolated mitochondria from rat liver. The results show that the HFP represents a mitochondrial compartment less sensitive to changes in energy states. In addition, it is concluded that the use of Rh-123 to monitor changes in mitochondrial membrane potential should be undertaken with caution because, under certain circumstances, there is no correlation between the Rh-123 intensity of fluorescence due to its uptake by mitochondria and previously reported changes in the mitochondrial membrane potential.

Bile acid-induced depolarization of mitochondrial membrane potential preceding cell injury in cultured gastric mucosal cells

Changes in energy metabolism elicited by sodium taurocholate and their relation to cell viability were determined in gastric mucosal cells. Cultured mucosal cells were labelled with rhodamine-123, a mitochondrial energization-sensitive fluorescence probe, or by propidium iodide, a fluorochrome which labels the nuclei of non-viable cells. The cells were observed under a fluorescence microscope with a laser scanning confocal imaging system. After the addition of sodium taurocholate at concentrations > 5 mol/L, mucosal cells showed a rapid and significant decrease in rhodamine-123 fluorescence. A decrease to 40% of the pretreated values at 30 min was seen with a concentration of sodium taurocholate of 7.5mmol/L. A marked increase in the percentage of propidium iodide-positive cells was noted when the concentration of sodium taurocholate exceeded 5mmol/L. However, the extent of the decrease in rhodamine-123 fluorescence was always greater than the increase in the percentage of propidium iodide-positive cells, suggesting that most of these gastric mucosal cells remained viable. It is therefore suggested that the decrease in rhodamine-123 fluorescence is largely due to the disturbed oxidative phosphorylation of mitochondria. Pretreatment of gastric mucosal cells with low concentrations of ethanol resulted in a significant cytoprotective effect against sodium taurocholate injury with significant prevention of a decrease in rhodamine-123 fluorescence. It is concluded that sodium taurocholate induces a depolarization of the mitochondrial membrane potential preceding cell injury and that the cytoprotective effect of ethanol relates to its attenuation of the uncoupling effect.

Decoupling of the bc1 complex in S. cerevisiae; point mutations affecting the cytochrome b gene bring new information about the structural aspect of the proton translocation

Four mutations in the mitochondrial cytochrome b of S. cerevisiae have been characterized with respect to growth capacities, catalytic properties, ATP/2e- ratio, and transmembrane potential. The respiratory-deficient mutant G137E and the three pseudo-wild type revertants E137 + I147F, E137 + C133S, and E137 + N256K were described previously (Tron and Lemesle-Meunier, 1990; Di Rago et al., 1990a). The mutant G137E is unable to grow on respiratory substrates but its electron transfer activity is partly conserved and totally inhibited by antimycin A. The secondary mutations restore the respiratory growth at variable degree, with a phosphorylation efficiency of 12-42% as regards the parental wild type strain, and result in a slight increase in the various electron transfer activities at the level of the whole respiratory chain. The catalytic efficiency for ubiquinol was slightly (G137E) or not affected (E137 + I147F, E137 + C133S, and E137 + N256K) in these mutants. Mutation G137E induces a decrease in the ATP/2e- ratio (50% of the W.T. value) and transmembrane potential (60% of the W.T. value) at the bc1 level, whereas the energetic capacity of the cytochrome oxidase is conserved. Secondary mutations I147F, C133S, and N256K partly restore the ATP/2e- ratio and the transmembrane potential at the bc1 complex level. The results suggest that a partial decoupling of the bc1 complex is induced by the cytochrome b point mutation G137E. In the framework of the protonmotive Q cycle, this decoupling can be explained by the existence of a proton wire connecting centers P and N in the wild type bc1 complex which may be amplified or uncovered by the G137E mutation when the bc1 complex is functioning.

Modification of rhodamine staining allows identification of hematopoietic stem cells with preferential short-term or long-term bone marrow-repopulating ability

We have developed a modified rhodamine (Rho) staining procedure to study uptake and efflux in murine hematopoietic stem cells. Distinct populations of Rho++ (bright), Rho+ (dull), and Rho- (negative) cells could be discriminated. Sorted Rho- cells were subjected to a second Rho staining procedure with the P-glycoprotein blocking agent verapamil (VP). Most cells became Rho positive [Rho-/Rho(VP)+ cells] and some remained Rho negative [Rho-/Rho(VP)- cells]. These cell fractions were characterized by their marrow-repopulating ability in a syngeneic, sex-mismatch transplantation model. Short-term repopulating ability was determined by recipient survival for at least 6 weeks after lethal irradiation and transplantation--i.e., radioprotection. Long-term repopulating ability at 6 months after transplantation was measured by fluorescence in situ hybridization with a Y-chromosome-specific probe, by graft function and recipient survival. Marrow-repopulating cells were mainly present in the small Rho- cell fraction. Transplantation of 30 Rho- cells resulted in 50% radioprotection and > 80% donor repopulation in marrow, spleen, and thymus 6 months after transplantation. Cotransplantation of cells from both fractions in individual mice directly showed that within this Rho- cell fraction, the Rho-/Rho(VP)+ cells exhibited mainly short-term and the Rho-/Rho(VP)- cells exhibited mainly long-term repopulating ability. Our results indicate that hematopoietic stem cells have relatively high P-glycoprotein expression and that the cells responsible for long-term repopulating ability can be separated from cells exhibiting short-term repopulating ability, probably by a reduced mitochondrial Rho-binding capacity.

Nitric oxide mediates mitochondrial dysfunction in hepatoma cells induced by non-activated Kupffer cells: evidence implicating ICAM-1-dependent process

The metabolic changes in a rat hepatoma cell line, AH70 cells, after co-culture with rat Kupffer cells (KC) were visualized and analysed using a fluorescence microscope equipped with a silicon intensified target camera and a laser scanning confocal microscopic system. Kupffer cells were isolated from male Wistar rats, and cultured without any stimuli. The non-activated KC reduced the mitochondrial energization in the cocultured AH70 cells within 2 h, which was indicated by decreased rhodamine 123 (Rh123) fluorescence. Either NG-monomethyl-L-arginine or dexamethasone significantly attenuated the KC-induced mitochondrial dysfunction in AH70 cells, suggesting the involvement of nitric oxide (NO) derived from inducible-type nitric oxide synthase (iNOS). Administration of monoclonal antibody (mAb) directed against rat ICAM-1 also prevented the decrease in Rh123 fluorescence. Electron microscopy revealed that the membrane-to-membrane attachment between KC and AH70 cells occurred within 2 h. A laser scanning confocal microscopic observation using mAb against ICAM-1 presented that the ICAM-1 expression on AH70 cells and KC increased after the co-culture. It is therefore concluded that the KC-mediated mitochondrial dysfunction of hepatoma cells largely depends on NO production by iNOS. Furthermore, the present study supports a scenario that the NO production and release from KC is triggered by the close contact with hepatoma cells through adhesion molecules such as ICAM-1.

Effects of the anaesthetic propofol on the calcium-induced permeability transition of rat heart mitochondria: direct pore inhibition and shift of the gating potential

Mitochondrial calcium exchanges are involved in intracellular calcium homeostasis and in the contraction-relaxation process in myocytes. The calcium-induced permeability transition of the heart mitochondria inner membrane appears to be an important calcium efflux mechanism involved in some physiological and pathological situations. The negative inotropic effect of the anaesthetic propofol results in part from a decrease in intracellular calcium availability. Thus, this study evaluates the effects of propofol on calcium transport and permeability transition of heart mitochondria. The propofol-inhibition of the permeability transition of liver mitochondria was previously investigated [Eriksson, O. (1991) FEBS Lett. 279, 45-48] in such conditions that its uncoupling effect was not taken into account. We show here that propofol uncoupling results in a decrease in calcium uptake rate which could in part explain the decreased permeability transition rate. However, comparison of equipotent uncoupling concentrations of propofol and carbonylcyanide m-chlorophenylhydrazone reveals that beyond this uncoupling effect, propofol has a direct inhibitory action on the permeability transition pore, concomittant with a shift of its gating potential.

Chimeric green fluorescent protein as a tool for visualizing subcellular organelles in living cells

BACKGROUND

It has recently been demonstrated that the green fluorescent protein (GFP) of the jellyfish Aequorea victoria retains its fluorescent properties when recombinantly expressed in both prokaryotic (Escherichia coli) and eukaryotic (Caenorhabditis elegans and Drosophila melanogaster) living cells; it can therefore be used as a powerful marker of gene expression in vivo. The specific targeting of recombinant GFP within cells would allow it to be used for even more applications, but no information is yet available on the possibility of targeting GFP to intracellular organelles.

RESULTS

In this study, we show that the GFP cDNA can be expressed at high levels in cultured mammalian cells; the recombinant polypeptide is highly fluorescent and is exclusively localized in the cytosol. Furthermore, we have modified the GFP cDNA to include a mitochondrial targeting sequence (and a strong immunological epitope at the amino terminus of the encoded polypeptide). When transiently transfected into mammalian cells, this construct drives the expression of a strongly fluorescent GFP chimera which selectively localizes to the mitochondria. We also describe two of the many possible applications of this recombinant GFP in physiological studies. The targeted chimera allows the visualization of mitochondrial movement in living cells. Also, unlike dyes such as rhodamine, it reveals morphological changes induced in mitochondria by drugs that collapse the organelle membrane potential. Moreover, when GFP is cotransfected with a membrane receptor, such as the alpha 1-adrenergic receptor, the fluorescence of the GFP in intact cells can be used in recognizing the transfected cells. Thus, specific changes in intracellular Ca2+ concentration that occur in cells expressing the recombinant receptor can be identified using a classical fluorescent Ca2+ indicator.

CONCLUSION

GFP is an invaluable new tool for studies of molecular biology and cell physiology. As a marker of transfection in vivo, it provides a simple means of identifying genetically modified cells to be used in physiological studies. More importantly, chimeric GFP, which in principle can be targeted to any subcellular location, can be used to monitor complex phenomena in intact living cells, such as changes in shape and distribution of organelles, and it has the potential to be used as a probe of physiological parameters.

ATP opens an electrophoretic potassium transport pathway in respiring yeast mitochondria

In the presence of KCl and only at low phosphate concentrations, ATP stimulated state 4 of the respiration of isolated yeast mitochondria. This effect could be related to a partial collapse of the transmembrane potential which was created by the respiratory chain or the F0F1-ATPase. Sodium and lithium could not replace potassium ion. Atractyloside prevented the opening of this K+ pathway, suggesting that only matricial ATP operated. All these effects were inhibited by increasing phosphate concentration, or by adding propranolol, quinine, Zn2+ or Mg2+.

Inhibition of plasma membrane and mitochondrial transmembrane potentials by ethanol

The actions of ethanol and its primary oxidative metabolite, acetaldehyde, on plasma membrane and mitochondrial transmembrane potentials were examined in rat brain using fluorescence techniques. Subchronic treatment of adult rats with ethanol resulted in a significant depolarization of both the plasma and mitochondrial membranes when the mean blood ethanol level of the rats was 59 +/- 11 mM (mean +/- SEM, n = 6). Acute dosing of animals (4.5 g/kg, i.p.) failed to show any significant alterations. Various concentrations of ethanol, added in vitro to a crude synaptosomal preparation isolated from the rat cerebrocortex (P2) from untreated animals, depolarized both the plasma and mitochondrial transmembrane potentials in a dose-related manner. Addition of acetaldehyde in vitro did not reveal any significant effects on plasma or mitochondrial transmembrane potential.

Microvascular responses to inhibition of nitric oxide production. Role of active oxidants

The objective of this study was to assess the potential contribution of hydrogen peroxide (H2O2) to the leukocyte-endothelial cell adhesion and increased microvascular permeability observed in rat mesenteric venules after inhibition of nitric oxide synthesis with NG-nitro-L-arginine methyl ester (L-NAME). Leukocyte adherence and emigration and leakage of fluorescein isothiocyanate-labeled albumin were monitored in postcapillary venules before and after exposure of the tissue to L-NAME. H2O2 production in mesenteric tissue was monitored by using dihydrorhodamine 123 (DHR), the H2O2-sensitive fluorochrome. L-NAME elicited a rapid increase in both the rate of albumin extravasation and oxidation of DHR, which was followed by an increased adherence and emigration of leukocytes in postcapillary venules. Treatment with either catalase or dimethylthiourea attenuated the L-NAME-induced oxidative stress, albumin leakage, and leukocyte-endothelial cell adhesion. Oxidation of DHR was enhanced in animals treated with either 3-amino-1,2,4-triazole (ATZ), an inhibitor of endogenous catalase, or a combination of ATZ and maleic acid diethyl ester, which depletes intracellular glutathione. Animals receiving a CD11/CD18-specific antibody to prevent leukocyte adhesion/emigration exhibited a reduced oxidation of DHR in response to L-NAME. These findings indicate that most of the H2O2 (and secondarily derived oxidants) generated in mesenteric tissue exposed to an inhibitor of nitric oxide production is due to accumulation of activated leukocytes.

The role of redox cycling versus arylation in quinone-induced mitochondrial dysfunction: a mechanistic approach in classifying reactive toxicants

In an attempt to distinguish between the mechanisms by which electrophilic and redox cycling quinones induce the cyclosporine A (CyA)-sensitive mitochondrial membrane permeability transition, the ability of a series of quinones that span a broad range of electrophilic and redox cycling reactivities has been examined. The order of potency of quinone-induced Ca2+ release was 1,4-naphthoquinone (NQ) > 1,4-benzoquinone (BQ) > 2-methyl-1,4-naphthoquinone (MQ) > 2,3-dimethoxy-1,4-naphthoquinone (DiOMeNQ) > 2,3-dimethyl-1,4-naphthoquinone (DiMeNQ). Quinones with predominantly redox cycling reactivity, NQ ( < or = 4 microM), MQ, DiOMeNQ and DiMeNQ, induced the CyA-sensitive membrane permeability transition. In contrast, NQ ( > 4 microM) and BQ, induced rapid and complete Ca2+ release and membrane depolarization, but not swelling. Furthermore, BQ and NQ ( > 4 microM)-induced effects were not prevented by CyA. Therefore, we maintain that, unlike MQ, DiOMeNQ, DiMeNQ and NQ ( < or = 4 microM), effects of BQ and NQ( > 4 microM) on calcium flux and membrane potential are manifest via a mechanism independent of altering the regulation of the cyclosporine A-sensitive PTP. These findings suggest that stereoelectronic descriptors for soft electrophilicity and one electron reduction potential may be useful in differentiating and predicting mechanisms of quinone toxicity.

Scanning microspectrofluorometry of rhodamine 123 in multidrug-resistant cells

Scanning microspectrofluorometry has been developed to perform the mapping of fluorescence spectra from all locations in a living cell. This new method has been applied to study the molecular environment of rhodamine 123 (R123) in sensitive (K562, CEM) and multidrug-resistant (K562-R, CEM/VLB100) tumor cells. All cells exposed to R123 showed a similar distribution of fluorescence in the perinuclear region. A lower cytoplasmic fluorescence intensity corresponding to a reduced drug accumulation was observed in resistant cells, as expected in the multidrug resistance process. Fluorescence emission spectra of R123 are useful to probe the polarity of the R123 environment. Thus, fluorescence spectra of R123-treated cells have been analyzed as a linear combination of model spectra: R123 in water and R123 in tensio-active Triton X-100. In sensitive cells, emission spectra of R123 underwent a red shift, equivalent to those observed in isolated coupled mitochondria. This suggests the formation of a complex in hydrophobic sites. In contrast, R123 spectra were less shifted in resistant cells, showing two types of both hydrophobic and hydrophilic binding sites. This could be related to an intracellular redistribution of R123 in resistant cells.

Antibacterial peptides and mitochondrial presequences affect mitochondrial coupling, respiration and protein import

Cecropins A and P1, antibacterial peptides from insects and from pig and some related peptides released respiratory control, inhibited protein import and at higher concentrations also inhibited respiration. However, PR-39, an antibacterial peptide from pig intestine, was found to be almost inert towards mitochondria. The concentrations at which the three mitochondrial functions were effected varied for different peptides. Melittin, magainin and Cecropin-A-(1,13)-Melittin(1,13)-NH2, a hybrid between cecropin A and melittin, were most potent, while the two cecropins acted at higher concentrations. The biosynthesis of cecropin A is known and the intermediates are synthesized. We have used four peptides from this pathway to investigate their effects on coupling, respiration and protein import into mitochondria. Mature cecropin A followed by the preproprotein were most aggressive whereas the intermediates were less active or inert. The efficiency of different derivatives of cecropin A as uncouplers correlates well with their capacity to release membrane potential measured as fluorescence quenching of Rhodamine 123. Inhibition of respiration was found to be dependent on membrane potential and was most pronounced with mature cecropin A, less so with its three precursors. We also found that three peptides derived from mitochondrial presequences showed antibacterial activity. It is concluded that, there are similarities in the functions of antibacterial peptides and mitochondrial presequences, uncoupling activity in mitochondria cannot be correlated with the antibacterial activity (contrary to a previous suggestion), the processing of preprocecropin A may have evolved in such a way that there is a minimum of membrane damage from the intermediates in the pathway, and peptides produced for delivery outside of an animal have evolved to be more aggressive against mitochondria than peptides for delivery inside of the animal.

Antibodies against subunits of F0 sector of ATP synthase from Saccharomyces cerevisiae. Stimulation of ATP synthase by subunit-8-reactive antibodies and inhibition by subunit-9-reactive antibodies

Polyclonal antibodies against the three purified proteolipids of the F0 sector [subunit 6 (Su6), subunit 8 (Su8), subunit 9 (Su9)] and against the beta subunit (F1) of ATP synthase were raised in rabbits. All antisera showed ELISA reactivities with F0F1-ATPase. Antisera used to immunoblot partially purified ATP synthase labeled a single band migrating with the same molecular mass as that of the purified protein. Mitochondria were incubated with IgG of each antiserum and oxidative phosphorylation was measured. Anti-Su6 IgG, as anti-Su beta IgG, was without effect whereas anti-Su9 IgG decrease both respiration and ATP-synthesis rates, resulting in a decrease of ATP/O. In contrast, anti-Su8 IgG enhanced respiratory control and stimulated the ATP-synthesis rate, resulting in an increase of ATP/O. In the same manner, anti-Su9 IgG inhibited ATP hydrolysis whereas anti-Su8 IgG stimulated this activity. Antimycin titration of phosphorylation and respiration rates demonstrated that anti-Su9 IgG decreased the H+/ATP ratio and promoted a H+ leak, whereas anti-Su8 IgG increased H+/ATP without modification of the proton permeability. Anti-Su9 IgG decreased proton-motive force whereas anti-Su8 IgG did not. It is proposed that both antibodies promoted opposite mechanistic changes of the H+/ATP stoichiometry of the ATP synthase, and that in vivo Su8 could have a negative regulatory role in the oxidative phosphorylation process.

Unidirectional fluxes of rhodamine 123 in multidrug-resistant cells: evidence against direct drug extrusion from the plasma membrane

P-glycoprotein (Pgp), a plasma membrane protein overexpressed in multidrug-resistant tumor cells, is an ATPase thought to actively export cytotoxic drugs. It has been proposed that Pgp transports drugs directly from the lipid bilayer to the external medium ("vacuum cleaner" hypothesis). A possible mechanism for this model is that the Pgp is a flippase--i.e., it catalyzes the translocation of hydrophobic substrates from the inner to the outer leaflet of the cell membrane. Two immediate predictions of the vacuum cleaner and flippase hypotheses are that the apparent unidirectional influx of substrate should be less in Pgp-expressing than in Pgp-lacking cells and that this difference should be abolished by inhibition of the Pgp. We used Chinese hamster fibroblasts with different levels of Pgp expression to measure true unidirectional fluxes of rhodamine 123 (R123), a Pgp-transported fluorescent dye that accumulates in mitochondria (hence, its cytosolic concentration remains low at short times after external addition). The unidirectional efflux of R123 was proportional to the level of Pgp expression and was reduced by Pgp inhibitors. The unidirectional influx of R123 was the same in sensitive and resistant cells--i.e., independent of the level of Pgp expression and insensitive to inhibitors of R123 efflux. From these results, we rule out the vacuum cleaner and flippase hypotheses and conclude that Pgp extracts the actively transported substrates from the cytosol and not from the plasma membrane.

Postnatal changes in rhodamine-123 stained mitochondrial populations are sensitive to protein synthesis inhibitors but mimicked in vitro by ATP

The incubation of term fetus mitochondria with ATP mimicked in vitro the increase in the respiratory control index and in the percentage of the rhodamine-123-low fluorescence population that occurred in vivo immediately after birth, suggesting that both phenomena are closely associated. The administration of streptomycin inhibited the increase in the percentage of the low fluorescence population that occurred immediately after birth, while the administration of cycloheximide even reversed these changes. These results suggest that the in vivo interconversion between mitochondrial forms depends on both cytosolic and mitochondrial protein synthesis.

Distribution of electrical potential, pH, free Ca2+, and volume inside cultured adult rabbit cardiac myocytes during chemical hypoxia: a multiparameter digitized confocal microscopic study

Exploiting the optical sectioning capabilities of laser scanning confocal microscopy and using parameter-specific fluorescent probes, we determined the distribution of pH, free Ca2+, electrical potential, and volume inside cultured adult rabbit cardiac myocytes during ATP depletion and reductive stress with cyanide and 2-deoxyglucose ("chemical hypoxia"). During normoxic incubations, myocytes exhibited a cytosolic pH of 7.1 and a mitochondrial pH of 8.0 (delta pH = 0.9 units). Sarcolemmal membrane potential (delta psi) was -80 mV, and mitochondrial delta psi was as high as -100 mV, yielding a mitochondrial protonmotive force (delta p) of -155 mV (delta P = delta psi - 60 delta pH). After 30 min of chemical hypoxia, mitochondrial delta pH decreased to 0.5 pH units, but mitochondrial delta psi remained essentially unchanged. By 40 min, delta pH was collapsed, and mitochondrial and cytosolic free Ca2+ began to increase. Mitochondrial and sarcolemmal delta psi remained high. as Ca2+ rose, myocytes shortened, hypercontracted, and blebbed with a 30% decrease of cell volume. After hypercontraction, extensive mitochondrial Ca2+ loading occurred. After another few minutes, mitochondrial depolarized completely and released their load of Ca2+. After many more minutes, the sarcolemmal permeability barrier broke down, and viability was lost. These studies demonstrate a sequence of subcellular ionic and electrical changes that may underlie the progression to irreversible hypoxic injury.

A fast kinetic method for assessing mitochondrial membrane potential in isolated hepatocytes with rhodamine 123 and flow cytometry

Rhodamine 123 (Rh123) is widely used as a flow cytometric probe for mitochondrial membrane potential (MMP) in metabolic, pharmacologic, and toxicological studies. However, the use of relatively high concentrations of Rh123 (up to 10 micrograms/ml) and prolonged incubation times (up to 1 h), including washing steps, may be inconvenient for certain applications in which labile cells are used or which demand rapid or repeated analysis. In this paper we describe a rapid kinetic assay of MMP in isolated rat hepatocytes, based upon the quantitation of the initial rate of Rh123 uptake by living cells, selected by their scattering properties. The results indicate that at an appropriate dye-to-cell ratio (in our experiments, 50 ng Rh123/ml for 250,000-300,000 cells/ml), the initial rate of Rh123 uptake is a highly reproducible and sensitive parameter for estimation of MMP, as demonstrated by the effects of substrates and inhibitors of the glycolytic pathway and mitochondrial respiration. Because of its simplicity, rapidity (about 5 min) and metabolic implications, this assay would be also suitable for the routine evaluation of metabolic state of cell suspensions, as a complementary test to the standard dual-staining tests of viability. Other possible applications in screening pharmacologic and toxicological analysis are discussed.

The antiviral activity of RNA-dye combinations

The results of our previous studies (Jamison et al. 1988, 1989, 1990 a, b, c, d, e) have shown that the ability of intercalative dyes to modulate the antiviral activity of poly r(A-U) is related to the groove through which the dyes intercalate into the poly r(A-U). When poly r(A-U) is combined with the minor groove intercalating dyes or the minor/major groove intercalating dyes, optimum enhancement of antiviral activity is observed at the dye/ribonucleotide ratio predicted by the neighbor exclusion model (usually 1/4 or 1/6). No enhancement is observed when poly r(A-U) is combined with major groove intercalating dyes. When poly r(A-U) is combined with additional intercalative dyes to produce a dye/ribonucleotide ratio of 1/4 and a ribonucleotide concentration of 200 microM, the antiviral activity of poly r(A-U) is enhanced 8- to 20-fold, while 50% effective doses of the poly r(A-U) and the dyes decreases 18- to 347-fold. Interferon neutralization assays demonstrate that the interferon-inducing capability of the dye/poly r(A-U) combinations approximates the sum of the interferon-inducing capabilities of the poly r(A-U) and the dyes employed and suggests that the dyes potentiate the antiviral activity of poly r(A-U) without affecting the amount of interferon induced. Direct viral inactivation studies demonstrate that the dyes, poly r(A-U), and the dye/poly r(A-U) combinations do not inactivate VSV at concentrations near the 50% viral inhibitory dose. Assessment of cytotoxicity by microscope examination of HSF cell morphology and trypan blue exclusion indicates that the dye/poly r(A-U) combinations exhibit antiviral activity at concentrations well below those that induce cyto-toxicity. Several of the dyes and the dye/poly r(A-U) combinations exhibit anti-HIV-1 activity, suggesting that the enhancement phenomenon is not virus-specific nor host cell-specific. The enhancement phenomenon is sensitive to the base sequence of the polynucleotide with dye/poly r(A-U) and dye/poly r(G-C) combinations displaying enhanced antiviral activity, while dye/poly (rI).poly (rC) and dye/poly d(A-T) combinations do not. These results suggest that while intercalation of the dye and interferon induction are necessary for enhanced antiviral activity, neither intercalation nor interferon induction alone is sufficient to potentiate the antiviral activity of polyribonucleotides.

Prostaglandin E1 abrogates early reductive stress and zone-specific paradoxical oxidative injury in hypoperfused rat liver

This study was designed to investigate the effects of prostaglandin E1 on reductive stress and the subsequent oxidative cell injury in hypoperfused rat liver. The intralobular heterogeneity of hepatocellular redox state, mitochondrial dysfunction, and intracellular hydroperoxide formation were visually monitored by digital microfluorography of pyridine nucleotide autofluorescence, rhodamine 123, and dichlorofluorescein fluorescence, respectively. Under the 25% low flow perfusion, pyridine nucleotide autofluorescence increased time-dependently and reached a steady state at 10 min among the entire lobules. The decrease in mitochondrial membrane potential was > 20 mV in all portions of the lobules at 60 min. The onset of hydroperoxide formation was observed at 40 min in the marginally oxygenated proximal portion of anoxic pericentral regions and the oxidative impact reached a maximum level at 60 min. Sodium (-)-8-(3-methoxy-4-phenylsulfinylphenyl) pyrazo [1,5-a]-1,3,5-triazine-4-olate monohydrate (BOF 4272), a novel xanthine oxidase inhibitor, suppressed the zone-specific oxidative changes without attenuating the increase in pyridine nucleotide autofluorescence and mitochondrial dysfunction. Pretreatment with prostaglandin E1 not only abrogated an early increase in pyridine nucleotide fluorescence and mitochondrial dysfunction induced by hypoperfusion but also diminished the subsequent midzonal oxidative injury. Since prostaglandin E1 has no oxyradical-scavenging action, the preventive effect of this reagent on the hypoxia-induced oxidative cell injury is attributable to the attenuation of mitochondrial dysfunction. These results suggest that, in low flow hypoxia, early reductive stress plays a key role in the initiation of xanthine oxidase-mediated midzonal oxidative changes, which may lead to subsequent centrilobular necrosis.

The TF1-ATPase and ATPase activities of assembled alpha 3 beta 3 gamma, alpha 3 beta 3 gamma delta, and alpha 3 beta 3 gamma epsilon complexes are stimulated by low and inhibited by high concentrations of rhodamine 6G whereas the dye only inhibits the alpha 3 beta 3, and alpha 3 beta 3 delta complexes

The ATPase activity of the F1-ATPase from the thermophilic bacterium PS3 is stimulated at concentrations of rhodamine 6G up to about 10 microM where 70% stimulation is observed at 36 degrees C. Half maximal stimulation is observed at about 3 microM dye. At rhodamine 6G concentrations greater than 10 microM, ATPase activity declines with 50% inhibition observed at about 75 microM dye. The ATPase activities of the alpha 3 beta 3 gamma and alpha 3 beta 3 gamma delta complexes assembled from isolated subunits of TF1 expressed in E. coli deleted of the unc operon respond to increasing concentrations of rhodamine 6G nearly identically to the response of TF1. In contrast, the ATPase activities of the alpha 3 beta 3 and alpha 3 beta 3 delta complexes are only inhibited by rhodamine 6G with 50% inhibition observed, respectively, at 35 and 75 microM dye at 36 degrees C. The ATPase activity of TF1 is stimulated up to 4-fold by the neutral detergent, LDAO. In the presence of stimulating concentrations of LDAO, the ATPase activity of TF1 is no longer stimulated by rhodamine 6G, but rather, it is inhibited with 50% inhibition observed at about 30 microM dye at 30 degrees C. One interpretation of these results is that binding of rhodamine 6G to a high-affinity site on TF1 stimulates ATPase activity and unmasks a low-affinity, inhibitory site for the dye which is also exposed by LDAO.

Assessment of ram sperm mitochondrial function by quantitative determination of sperm rhodamine 123 accumulation

A simple procedure is described for determining the functional state of ram sperm mitochondria by quantitative measurement of sperm rhodamine 123 (R 123) accumulation. Sperm were incubated with 1 microgram/ml R 123, and the accumulated R 123 was measured fluorimetrically after release from washed sperm by detergent lysis. Ram sperm R 123 uptake was maximal after 30 min of incubation and responded to changes in both sperm (P < 0.01) and R 123 (P < 0.01) concentration. There was a linear relationship (r = 0.98) between R 123 uptake and the proportion of cold-shocked sperm present in a sperm sample. R 123 uptake was unaffected by 20 mM 2-deoxyglucose or by 10 mM malonate (the latter being sufficient to reduce O2 uptake; P < 0.01). R 123 accumulation in ram sperm was reduced by 6 mg/ml sodium pentobarbitone (P < 0.05), by 1 microM 2,4-dinitrophenol (P < 0.01), and by 0.05% Triton X-100 (P < 0.01). It is concluded that quantitative estimation of R 123 uptake complements oxygen uptake in detecting mitochondrial dysfunction in ram sperm. While it is largely unaffected by inhibition of glycolysis, and is less sensitive than oxygen uptake to trichloroacetic acid cycle inhibition, R 123 uptake is sensitive to factors directly reducing the mitochondrial membrane potential of ram sperm. It may therefore by useful in the evaluation of the effects of such membrane-mediated injuries as cold shock and freezing damage on ram sperm mitochondria.