Uncoupling of oxidative phosphorylation

Antimicrobial cetylpyridinium chloride causes functional inhibition of mitochondria as potently as canonical mitotoxicants, nanostructural disruption of mitochondria, and mitochondrial Ca2+ efflux in living rodent and primary human cells

People are exposed to high concentrations of antibacterial agent cetylpyridinium chloride (CPC) via food and personal care products, despite little published information regarding CPC effects on eukaryotes. Here, we show that low-micromolar CPC exposure, which does not cause cell death, inhibits mitochondrial ATP production in primary human keratinocytes, mouse NIH-3T3 fibroblasts, and rat RBL-2H3 immune mast cells. ATP inhibition via CPC (EC50 1.7 μM) is nearly as potent as that caused by canonical mitotoxicant CCCP (EC50 1.2 μM). CPC inhibition of oxygen consumption rate (OCR) tracks with that of ATP: OCR is halved due to 1.75 μM CPC in RBL-2H3 cells and 1.25 μM in primary human keratinocytes. Mitochondrial [Ca2+] changes can cause mitochondrial dysfunction. Here we show that CPC causes mitochondrial Ca2+ efflux from mast cells via an ATP-inhibition mechanism. Using super-resolution microscopy (fluorescence photoactivation localization) in live cells, we have discovered that CPC causes mitochondrial nanostructural defects in live cells within 60 min, including the formation of spherical structures with donut-like cross section. This work reveals CPC as a mitotoxicant despite widespread use, highlighting the importance of further research into its toxicological safety.

Pyrazinoic acid, the active form of the anti-tuberculosis drug pyrazinamide, and aromatic carboxylic acid analogs are protonophores

Pyrazinoic acid is the active form of pyrazinamide, a first-line antibiotic used to treat Mycobacterium tuberculosis infections. However, the mechanism of action of pyrazinoic acid remains a subject of debate, and alternatives to pyrazinamide in cases of resistance are not available. The work presented here demonstrates that pyrazinoic acid and known protonophores including salicylic acid, benzoic acid, and carbonyl cyanide m-chlorophenyl hydrazone all exhibit pH-dependent inhibition of mycobacterial growth activity over a physiologically relevant range of pH values. Other anti-tubercular drugs, including rifampin, isoniazid, bedaquiline, and p-aminosalicylic acid, do not exhibit similar pH-dependent growth-inhibitory activities. The growth inhibition curves of pyrazinoic, salicylic, benzoic, and picolinic acids, as well as carbonyl cyanide m-chlorophenyl hydrazone, all fit a quantitative structure-activity relationship (QSAR) derived from acid-base equilibria with R2 values > 0.95. The QSAR model indicates that growth inhibition relies solely on the concentration of the protonated forms of these weak acids (rather than the deprotonated forms). Moreover, pyrazinoic acid, salicylic acid, and carbonyl cyanide m-chlorophenyl hydrazone all caused acidification of the mycobacterial cytoplasm at concentrations that inhibit bacterial growth. Thus, it is concluded that pyrazinoic acid acts as an uncoupler of oxidative phosphorylation and that disruption of proton motive force is the primary mechanism of action of pyrazinoic acid rather than the inhibition of a classic enzyme activity.

Nanoparticle-Driven Controllable Mitochondrial Regulation through Lysosome-Mitochondria Interactome

Precise subcellular manipulation remains challenging in quantitative biological studies. After target modification and hierarchical assembly, nanoparticles can be functionalized for intracellular investigation. However, it remains unclear whether nanoparticles themselves can progressively manipulate subcellular processes, especially organellar networks. Mitochondria act as the energetic supply, whose fission dynamics are often modulated by molecular reagents. Here, using different-sized gold nanoparticles (AuNPs) as a model, we demonstrated the nanoparticle-driven controllable regulation on mitochondria. Compared with molecular reagents, AuNPs could induce size-dependent mitochondrial fission without detectable cell injury, and this process was reversible along with intracellular AuNPs' clearance. Mechanistically, it was attributed to the AuNPs-induced enhanced organelle interactome between lysosomes and mitochondria. Lysosomal accumulation of AuNPs induced lysosomal swelling and lysosomal motility alterations, promoting mitochondrial fission through the increased "kiss" events during the "kiss-and-run" moving of the lysosome-mitochondria interactome. This study highlights the fundamental understanding to fully explore the intrinsic capability of nanoparticles by engineering their basic properties. Also, it provides practical guidance to investigate the delicate nanolevel regulation on biological processes.

In silico to In vivo development of a polyherbal against Haemonchus contortus

Haemonchus contortus is a major constraint in the development of small ruminant subsector due to significant production losses incurred by it. The present study explores the antiparasitic potential of three anthelmintic plants (Butea monosperma, Vitex negundo and Catharanthus roseus (L.) G.Don) against H. contortus taking albendazole as the standard. In silico molecular docking and pharmacokinetic prediction studies were conducted with known bioactive molecules of these plants (palasonin, vinblastine, vincristine, betulinic acid and ursolic acid) against Glutamate Dehydrogenase (GDH) and tubulin molecules of the parasite. Methanolic extracts of these herbs were fractionated (hexane, ethyl acetate, chloroform and methanol) and used in in vitro larvicidal studies. Based on the in vitro data, two herbal prototypes were developed and clinically tested. All the 5 ligand molecules showed better binding affnity for GDH and tubulin protein as compared with albendazole and shared similar binding site in the core of the GDH hexamer with slight variations. Albendazole approximately stacked against GLY190A residue, showing hydrophobic interactions with PRO157A and a Pi-cation electrostatic interaction with ARG390 along with four hydrogen bonds. Vincristine formed 2 pi-anionic electrostatic bonds with ASP158 of B and C subunits alongwith hydrogen bonding and hydrophobic interaction and an additional pi-anion electrostatic interaction at ASP158A for vinblastine. Albendazole bound to α-tubulin next to colchicine site whereas vinblastine is bound at the nearby laulimalide/peloruside site of the dimer. Betulinic acid showed lateral interaction between the H2-H3 loop of one alpha subunit and H10 of the adjacent alpha subunit of two tubulin dimers. Ursolic acid and palasonin bound at the intradimer N site of microtubulin involving the H1-H7 and H1-H2 zone, respectively. The in vitro studies demonstrated good dose dependent anthelmintic potential. Both the prototypes were quite efficacious in clearing the infection, keeping it to a minimal for more than 5 months, probably, through direct anthelmintic effect through GDH, tubulin depolymerization and uncoupling as well as indirectly through immunomodulation along with antioxidant and anti-inflammatory properties.

A protet-based, protonic charge transfer model of energy coupling in oxidative and photosynthetic phosphorylation

Textbooks of biochemistry will explain that the otherwise endergonic reactions of ATP synthesis can be driven by the exergonic reactions of respiratory electron transport, and that these two half-reactions are catalyzed by protein complexes embedded in the same, closed membrane. These views are correct. The textbooks also state that, according to the chemiosmotic coupling hypothesis, a (or the) kinetically and thermodynamically competent intermediate linking the two half-reactions is the electrochemical difference of protons that is in equilibrium with that between the two bulk phases that the coupling membrane serves to separate. This gradient consists of a membrane potential term Δψ and a pH gradient term ΔpH, and is known colloquially as the protonmotive force or pmf. Artificial imposition of a pmf can drive phosphorylation, but only if the pmf exceeds some 150-170mV; to achieve in vivo rates the imposed pmf must reach 200mV. The key question then is 'does the pmf generated by electron transport exceed 200mV, or even 170mV?' The possibly surprising answer, from a great many kinds of experiment and sources of evidence, including direct measurements with microelectrodes, indicates it that it does not. Observable pH changes driven by electron transport are real, and they control various processes; however, compensating ion movements restrict the Δψ component to low values. A protet-based model, that I outline here, can account for all the necessary observations, including all of those inconsistent with chemiosmotic coupling, and provides for a variety of testable hypotheses by which it might be refined.

Characterization of cometabolic degradation of p-cresol with phenol as growth substrate by Chlorella vulgaris

To investigate the potential application of Chlorella vulgaris in the treatment of coal gasification wastewater, the characteristics of phenol and p-cresol cometabolism by Chlorella vulgaris were studied, including phenol degradation, ammonia nitrogen removal, antioxidant enzyme activities, and phenol hydroxylase activity. The results showed that the highest tolerable concentrations of phenol and p-cresol for Chlorella vulgaris were 800 and 400 mg/L, respectively. During cometabolism, phenol at low concentrations (100 mg/L) significantly promoted the degradation of p-cresol. Meanwhile, the removal efficiency of ammonia nitrogen was approximately 60% and was not affected by variations in phenol concentration. Furthermore, the cometabolism of phenol and p-cresol was enhanced by improvement of phenol hydroxylase activity of Chlorella vulgaris after the addition of NaHCO₃ as an exogenous nutrient. Therefore, Chlorella vulgaris has a great potential for the biochemical treatment of coal gasification wastewater.

Acute Effects of Drugs on Caenorhabditis elegans Movement Reveal Complex Responses and Plasticity

Many drugs act very rapidly - they can turn on or off their targets within minutes in a whole animal. What are the acute effects of drug treatment and how does an animal respond to these? We developed a simple assay to measure the acute effects of drugs on C. elegans movement and examined the effects of a range of compounds including neuroactive drugs, toxins, environmental stresses and novel compounds on worm movement over a time period of 3 hr. We found a wide variety of acute responses. Many compounds cause rapid paralysis which may be permanent or followed by one or more recovery phases. The recoveries are not the result of some generic stress response but are specific to the drug e.g., recovery from paralysis due to a neuroactive drug requires neurotransmitter pathways whereas recovery from a metabolic inhibitor requires metabolic changes. Finally, we also find that acute responses can vary greatly across development and that there is extensive natural variation in acute responses. In summary, acute responses are sensitive probes of the ability of biological networks to respond to drug treatment and these responses can reveal the action of unexplored pathways.

Comparative toxic potency ranking of chlorophenols

Chlorophenols are prevalent in all media of the environment. The most common environmental source of pentachlorophenol (PCP) and other chlorinated phenols are via the lumber industry as a wood preservative and as a pesticide in plant production. The US Environmental Protection Agency’s (EPA) contaminant candidate list (CCL) includes a majority of these compounds as unregulated contaminants. Except for pentachlorophenol, there is a lack of human or animal data base which can be used for human health risk assessment. The specific aim of this study is to develop a rationale to use in vivo nonmammalian, in vitro mammalian and nonmammalian, micro-organism toxicity data base, structural activity, mechanistic and toxicokinetic data bases for developing a relative toxic potency ranking scheme of chlorophenols. Although the toxic potency of chlorophenols was found to increase with the number of chlorines, the potency decreases if the chlorines are attached in the ortho position of the molecules. Based on the LOAELs and mammalian in vitro data, the relative potency of chlorophenols determined to be best estimated by the ratios of log Kow to the 0.55 power. The relationship of the toxic potency derived from such an approach is largely presumptive.

Antimicrobial agent triclosan is a proton ionophore uncoupler of mitochondria in living rat and human mast cells and in primary human keratinocytes

Triclosan (TCS) is an antimicrobial used widely in hospitals and personal care products, at ~10 mm. Human skin efficiently absorbs TCS. Mast cells are ubiquitous key players both in physiological processes and in disease, including asthma, cancer and autism. We previously showed that non-cytotoxic levels of TCS inhibit degranulation, the release of histamine and other mediators, from rat basophilic leukemia mast cells (RBL-2H3), and in this study, we replicate this finding in human mast cells (HMC-1.2). Our investigation into the molecular mechanisms underlying this effect led to the discovery that TCS disrupts adenosine triphosphate (ATP) production in RBL-2H3 cells in glucose-free, galactose-containing media (95% confidence interval EC50 = 7.5-9.7 µm), without causing cytotoxicity. Using these same glucose-free conditions, 15 µm TCS dampens RBL-2H3 degranulation by 40%. The same ATP disruption was found with human HMC-1.2 cells (EC50 4.2-13.7 µm), NIH-3 T3 mouse fibroblasts (EC50 4.8-7.4 µm) and primary human keratinocytes (EC50 3.0-4.1 µm) all with no cytotoxicity. TCS increases oxygen consumption rate in RBL-2H3 cells. Known mitochondrial uncouplers (e.g., carbonyl cyanide 3-chlorophenylhydrazone) previously were found to inhibit mast cell function. TCS-methyl, which has a methyl group in place of the TCS ionizable proton, affects neither degranulation nor ATP production at non-cytotoxic doses. Thus, the effects of TCS on mast cell function are due to its proton ionophore structure. In addition, 5 µm TCS inhibits thapsigargin-stimulated degranulation of RBL-2H3 cells: further evidence that TCS disrupts mast cell signaling. Our data indicate that TCS is a mitochondrial uncoupler, and TCS may affect numerous cell types and functions via this mechanism. Copyright © 2015 John Wiley & Sons, Ltd.

Triclosan is a mitochondrial uncoupler in live zebrafish

Triclosan (TCS) is a synthetic antimicrobial agent used in many consumer goods at millimolar concentrations. As a result of exposure, TCS has been detected widely in humans. We have recently discovered that TCS is a proton ionophore mitochondrial uncoupler in multiple types of living cells. Here, we present novel data indicating that TCS is also a mitochondrial uncoupler in a living organism: 24-hour post-fertilization (hpf) zebrafish embryos. These experiments were conducted using a Seahorse Bioscience XF^e 96 Extracellular Flux Analyzer modified for bidirectional temperature control, using the XF96 spheroid plate to position and measure one zebrafish embryo per well. Using this method, after acute exposure to TCS, the basal oxygen consumption rate (OCR) increases, without a decrease in survival or heartbeat rate. TCS also decreases ATP-linked respiration and spare respiratory capacity and increases proton leak: all indicators of mitochondrial uncoupling. Our data indicate, that TCS is a mitochondrial uncoupler in vivo, which should be taken into consideration when assessing the toxicity and/or pharmaceutical uses of TCS. This is the first example of usage of a Seahorse Extracellular Flux Analyzer to measure bioenergetic flux of a single zebrafish embryo per well in a 96-well assay format. The method developed in this study provides a high-throughput tool to identify previously unknown mitochondrial uncouplers in a living organism. Copyright © 2016 John Wiley & Sons, Ltd.

Novel method for real-time monitoring of ATP release reveals multiple phases of autocrine purinergic signalling during immune cell activation

AIMS

The activation of immune cells must be tightly regulated to allow an effective immune defence while limiting collateral damage to host tissues. Cellular ATP release and autocrine stimulation of purinergic receptors are recognized as critical regulators of immune cell activation. However, the study of purinergic signalling has been hampered by the short half-life of the released ATP and its breakdown products as well as the lack of real-time imaging methods to study spatiotemporal dynamics of ATP release.

METHODS

To overcome these limitations, we optimized imaging methods that allow monitoring of ATP release with conventional microscopy using the recently developed small molecular ATP probes 1-2Zn(II) and 2-2Zn(II) for imaging of ATP in the extracellular space and release at the surface of living cells.

RESULTS

1-2Zn(II) allowed imaging of <1 μm ATP in the extracellular space, while 2-2Zn(II) provided unprecedented insights into the spatiotemporal dynamics of ATP release from neutrophils and T cells. Stimulation of these cells caused virtually instantaneous ATP release, which was followed by a second phase of ATP release that was localized to the immune synapse of T cells and the leading edge of polarized neutrophils. Imaging these ATP signalling processes along with mitochondrial probes provided evidence for a close spatial relationship between mitochondrial activation and localized ATP release in T cells and neutrophils.

CONCLUSION

We believe that these novel live cell imaging methods can be used to define the roles of purinergic signalling in immune cell activation and in the regulation of other complex physiological processes.

Mono- and dicationic Re(I)/(99m)Tc(I) tricarbonyl complexes for the targeting of energized mitochondria

The enhanced negative mitochondrial membrane potential of tumor cells can increase the cell accumulation of triphenylphosphonium (TPP) derivatives, which prompted us to investigate TPP-containing Re(I)/(99m)Tc organometallic compounds as probes for in vivo targeting of energized mitochondria. Novel compounds (Re1-Re4/Tc1-Tc4) were obtained with bifunctional chelators of the pyrazole-diamine (N,N,N-donors) and pyrazole-aminocarboxylic (N,N,O-donors) type, functionalized with TPP pharmacophores that have been introduced at the central amine of the chelators using different spacers. In this way, dicationic (Re1-Re2, Tc1-Tc2) and monocationic (Re3-Re4, Tc3-Tc4) complexes with variable lipophilicity were synthesized. The (99m)Tc complexes (Tc1-Tc4) are highly stable under physiological conditions and their chemical identification was done by HPLC comparison with the Re congeners (Re1-Re4), which were fully characterized by common analytical techniques (electrospray ionization mass spectrometry (ESI-MS), IR, multinuclear NMR). The in vitro biological evaluation of Tc1-Tc4 was performed in a panel of human tumor cell lines (PC-3, MCF-7 and H69), including cell lines overexpressing P-glycoprotein (MCF-7/MDR1 and H69/Lx4), and in isolated mitochondria. All the tested complexes showed a low to moderate cellular and mitochondrial uptake and did not undergo significant P-glycoprotein (Pgp)-mediated efflux processes. In particular, the dication Tc2 and the monocation Tc4 presented the highest cellular and mitochondrial uptake. Their cellular uptake was shown to depend on the mitochondrial (Δψm) and plasma membrane (Δψp) potentials. Altogether, the biological properties of these compounds suggest that they might be relevant for the design of radioactive metalloprobes for in vivo targeting of mitochondria.

Narcotic mechanisms of acute toxicity of chlorinated anilines in Folsomia candida (Collembola) revealed by gene expression analysis

In order to clarify the mechanisms of reproductive toxicity in a QSAR approach, the transcriptional signatures upon the 2 day exposure to the 28 days EC₅₀ of a series of increasingly chlorinated aniline compounds and 1,2,3,4-tetrachlorobenzene were measured in Folsomia candida. In general, the transcriptional patterns associated with all compounds revealed toxicity at the cellular membranes and hence components of narcosis type I, but a principal component analysis revealed a deviating response by the pentachloroaniline and 2,3,5,6-tetrachloroaniline exposure. Moreover the expression of a subset of mainly biotransformation related genes showed a significant relationship with the logK(ow,) which stresses the presence of narcosis type I. This was confirmed by GO term enrichment at the level of cellular component. Genes involved in the three phases of xenobiotic biotransformation exhibited strict compound specific transcription patterns, which may reflect biotransformation processes in F. candida. Additional toxic mechanisms were especially observed for the 2,3,5,6-tetrachloroaniline, which possible works as an uncoupler or inhibitor of electron transport systems, which is revealed by the up-regulation of genes that encode different members of the electron transport chain. The aniline and 2,3,4-trichloroaniline exposure caused the induction of genes in the ROS defense system. Additional toxicity mechanisms were less clear, but they include the attack of microbial pathogens for the six other compounds and for 2,3,5,6-tetrachloroaniline an effect on mitochondrial protein folding.

Identification of differential hepatic proteins in rare minnow (Gobiocypris rarus) exposed to pentachlorophenol (PCP) by proteomic analysis

Pentachlorophenol (PCP) is a ubiquitous contaminant that has been shown to lead to hepatoxicity and is implicated in the incidence of liver tumors in human. A number of previous studies have described the toxic effects of PCP based on conventional toxicological indices. However, little evidence on protein levels is available at present. For further understanding of mechanisms of action and identifying the potential protein biomarkers for PCP exposure, two-dimensional electrophoresis coupled with mass spectrometry has been used to identify proteins differentially expressed in the livers of rare minnow (Gobiocypris rarus) following PCP exposure of 0.5, 5, 50 μg/L. After comparison of the protein profiles from treated and control groups, 39 protein spots were found altered in abundance (>2-fold) from male and female PCP-treated groups. Matrix-assisted laser desorption/ionization (MALDI) tandem time-of-flight mass spectrometry (TOF/MS) analysis allowed the unambiguous identification, and 18 protein spots were identified successfully, 12 proteins in females and 6 proteins in males, respectively. These proteins were involved in transport, metabolism, response to oxidative stress and other biological processes. Of these proteins, four differentially expressed mRNA encoding proteins underwent quantitative analysis by quantitative real-time PCR (QRT-PCR). The consistent and discrepant results between mRNA and protein levels suggested that complicated regulatory mechanisms of gene expression were implicated in the response to PCP exposure. In addition, marked gender differences in response to PCP have been described from the comparison of the male and female liver protein profiles.

Expression profile of rat hippocampal neurons treated with the neuroprotective compound 2,4-dinitrophenol: up-regulation of cAMP signaling genes

2,4-Dinitrophenol (DNP) is classically known as a mitochondrial uncoupler and, at high concentrations, is toxic to a variety of cells. However, it has recently been shown that, at subtoxic concentrations, DNP protects neurons against a variety of insults and promotes neuronal differentiation and neuritogenesis. The molecular and cellular mechanisms underlying the beneficial neuroactive properties of DNP are still largely unknown. We have now used DNA microarray analysis to investigate changes in gene expression in rat hippocampal neurons in culture treated with low micromolar concentrations of DNP. Under conditions that did not affect neuronal viability, high-energy phosphate levels or mitochondrial oxygen consumption, DNP induced up-regulation of 275 genes and down-regulation of 231 genes. Significantly, several up-regulated genes were linked to intracellular cAMP signaling, known to be involved in neurite outgrowth, synaptic plasticity, and neuronal survival. Differential expression of specific genes was validated by quantitative RT-PCR using independent samples. Results shed light on molecular mechanisms underlying neuroprotection by DNP and point to possible targets for development of novel therapeutics for neurodegenerative disorders.

Effects of carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone on the growth inhibition in human pulmonary adenocarcinoma Calu-6 cells

Carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP) is an uncoupler of mitochondrial oxidative phosphorylation in eukaryotic cells. Here, we evaluated the in vitro effects of FCCP on the growth of Calu-6 lung cancer cells. FCCP inhibited the growth of Calu-6 cells with an IC(50) of approximately 6.64+/-1.84 microM at 72 h, as shown by MTT. DNA flow cytometric analysis indicated that FCCP induced G1 phase arrest below 20 microM of FCCP. Treatment with FCCP decreased the level of CDKs and cyclines in relation to G1 phase. In addition, FCCP not only increased the p27 level but also enhanced its binding with CDK4, which was associated with hypophosphorylation of Rb protein. While transfection of p27 siRNA inhibited G1 phase arrest in FCCP-treated cells, it did not enhance Rb phosphorylation. FCCP also efficiently induced apoptosis. The apoptotic process was accompanied with an increase in sub-G1 cells, annexin V staining cells, mitochondria membrane potential (MMP) loss and cleavage of PARP protein. All of the caspase inhibitors (caspase-3, -8, -9 and pan-caspase inhibitor) markedly rescued the Calu-6 cells from FCCP-induced cell death. However, knock down of p27 protein intensified FCCP-induced cell death. Moreover, FCCP induced the depletion of GSH content in Calu-6 cells, which was prevented by all of the caspase inhibitors. In summary, our results demonstrated that FCCP inhibits the growth of Calu-6 cells in vitro. The growth inhibitory effect of FCCP might be mediated by cell cycle arrest and apoptosis via decrease of CDKs and caspase activation, respectively. These findings now provide a better elucidation of the mechanisms involved in FCCP-induced growth inhibition in lung cancer.

Characterization of membrane potential-dependent uptake of the novel PET tracer 18F-fluorobenzyl triphenylphosphonium cation

PURPOSE

Mitochondrial dysfunction has been attributed a critical role in the etiology and pathogenesis of numerous diseases, and is manifested by alterations of the organelle's membrane potential (Deltapsi(m)). This suggests that Deltapsi(m) measurement can be highly useful for diagnostic purposes. In the current study, we characterized the capability of the novel PET agent (18)F-fluorobenzyl triphenylphosphonium ((18)F-FBnTP) to assess Deltapsi(m), compared with the well-established voltage sensor (3)H-tetraphenylphosphonium ((3)H-TPP).

METHODS

(18)F-FBnTP and (3)H-TPP uptake under conditions known to alter Deltapsi(m) and plasma membrane potential (Deltapsi(p)) was assayed in the H345 lung carcinoma cell line. (18)F-FBnTP biodistribution was assessed in CD1 mice using dynamic PET and ex vivo gamma well counting.

RESULTS

(18)F-FBnTP and (3)H-TPP demonstrated similar uptake kinetics and plateau concentrations in H345 cells. Stepwise membrane depolarization resulted in a linear decrease in (18)F-FBnTP cellular uptake, with a slope (-0.58+/-0.06) and correlation coefficient (0.94+/-0.07) similar (p>0.17) to those measured for (3)H-TPP (-0.63+/-0.06 and 0.96+/-0.05, respectively). Selective collapse of Deltapsi(m) caused a substantial decrease in cellular uptake for (18)F-FBnTP (81.6+/-8.1%) and (3)H-TPP (85.4+/-6.7%), compared with control. Exposure to the proapoptotic staurosporine, known to collapse Deltapsi(m), resulted in a decrease of 68.7+/-10.1% and 71.5+/-8.4% in (18)F-FBnTP and (3)H-TPP cellular uptake, respectively. (18)F-FBnTP accumulated mainly in kidney, heart and liver.

CONCLUSION

(18)F-FBnTP is a mitochondria-targeting PET radiopharmaceutical responsive to alterations in membrane potential with voltage-dependent performance similar to that of (3)H-TPP. (18)F-FBnTP is a promising new voltage sensor for detection of physiological and pathological processes associated with mitochondrial dysfunction, such as apoptosis, using PET.

Mitochondrial ATPase

Considerable progress has been made in recent years in our understanding of the phosphorylating apparatus in mitochondria, chloroplasts, and bacteria. It has become clear that the structure and the function of the ATP synthesizing apparatus in these widely divergent organisms is similar if not virtually identical. The subunit composition of F1, its molecular architecture, the location and function of substrate binding sites, as well as putative control sites, understanding of the component parts of the oligomycin-sensitive ATPase complex, and the role of these components in the function of the complex all are under active investigation in many laboratories. The developing information and the new insights provided have begun to permit experimental approaches, at the molecular level, to the mode of action of the ATPase in electron-transport-coupled ATP synthesis.

Metabolic effects of carbenoxolone in rat liver

The action of carbenoxolone on hepatic energy metabolism was investigated in the perfused rat liver and isolated mitochondria. In perfused livers, carbenoxolone (200-300 microM) increased oxygen consumption, glucose production and glycolysis from endogenous glycogen. Gluconeogenesis from lactate or fructose, an energy-dependent process, was inhibited. This effect was already evident at a concentration of 25 microM. The cellular ATP levels and the adenine nucleotide content were decreased by carbenoxolone, whereas the AMP levels were increased. In isolated mitochondria, carbenoxolone stimulated state IV respiration and decreased the respiratory coefficient with the substrates beta-hydroxybutyrate and succinate. The ATPase of intact mitochondria was stimulated, the ATPase of uncoupled mitochondria was inhibited, and the ATPase of disrupted mitochondria was not altered by carbenoxolone. These results indicate that carbenoxolone acts as an uncoupler of oxidative phosphorylation and, possibly, as an inhibitor of the ATP/ADP exchange system. The inhibitory action of carbenoxolone on mitochondrial energy metabolism could be contributing to induce the mitochondrial permeability transition (MPT), a key phenomenon in apoptosis. The results of the present study can explain, partly at least, the in vivo hepatotoxic actions of carbenoxolone that were found in a previous clinical evaluation.

Effects of the Kielmeyera coriacea extract on energy metabolism in the rat liver

Kielmeyera coriacea Mart is a medicinal plant of the Clusiacea (Guttiferae) family used by the native population of Brazil in the treatment of several tropical diseases such as malaria, schistosomiasis, leishmaniasis, and fungal or bacterial infections. Kielmeyera coriacea is also effective as an antidepressant drug. Extracts of the plant are rich in xanthones. Compounds of this class have been reported to inhibit mitochondrial energy metabolism. For this reason the action of the Kielmeyera coriacea extract on hepatic energy metabolism was investigated in the present work, using isolated rat liver mitochondria and the perfused rat liver. In perfused livers the extract (20-80 microg/ml) caused stimulation of oxygen consumption, inhibition of gluconeogenesis and stimulation of glycogenolysis and glycolysis. In isolated mitochondria the Kielmeyera coriacea extract (5-20 microg/ml) stimulated state IV respiration, reduced the ADP/O ratio and decreased the respiratory coefficient. The activities of succinate-oxidase, NADH-oxidase, NADH dehydrogenase and succinate dehydrogenase were inhibited. The ATPase of intact mitochondria was stimulated and the ATPase of uncoupled mitochondria was inhibited. The results of this investigation suggest that the Kielmeyera coriacea extract impairs the hepatic energy metabolism by acting as mitochondrial uncoupler and inhibitor of enzymatic activities linked to the respiratory chain. The impairment of mitochondrial energy metabolism could lead to adverse metabolic effects by the use of the crude extract, but it could equally be the basis of its antiprotozoan and antifungal effects.

Effects of uncoupling of mitochondrial energy conservation on the ultradian clock-driven oscillations in Saccharomyces cerevisiae continuous culture

Protonophores have several different perturbative effects on dissolved O2 concentrations in continuous cultures of Saccharomyces cerevisiae. As well as uncoupling energy conservation from mitochondrial electron transport in vivo, they reset ultradian clock-driven respiratory oscillations and produce cell cycle effects. Thus, additions at low concentration (1.25 microM) of either m-chlorocarbonyl-cyanide phenylhydrazone (CCCP) or 5-chloro-3-t-butyl-2-chloro-4(1)-nitrosalicylanilide (S13) led to phase resetting of the 48 min ultradian clock-driven respiratory oscillations. At 2.5 microM CCCP or 4 microM S13, transient inhibition of oscillatory respiration (for 5 h) preceded synchronisation of the cell division cycle seen as a slow (9 h period) wave that enveloped the 48 min oscillation. At still higher concentrations of CCCP (5 microM), the cell division cycle was prolonged by about 7 h, and during this phase, the respiratory oscillation became undetectable. The significance of these observations with respect to the time-keeping functions of the ultradian clock is discussed.

Ultradian metronome: timekeeper for orchestration of cellular coherence

Dynamic intracellular spatial and temporal organization emerges from spontaneous synchronization of a massive array of weakly coupled oscillators; the majority of subcellular processes are implicated in this integrated expression of cellular physiology. Evidence for this view comes mainly from studies of Saccharomyces cerevisiae growing in self-synchronized continuous cultures, in which a temperature-compensated ultradian clock (period of approximately 40 min) couples fermentation with redox state in addition to the transcriptome and cell-division-cycle progression. Functions for ultradian clocks have also been determined in other yeasts (e.g. Schizosaccharomyces pombe and Candida utilis), seven protists (e.g. Acanthamoeba castellanii and Paramecium tetraurelia), as well as cultured mammalian cells. We suggest that ultradian timekeeping is a basic universal necessity for coordinated intracellular coherence.

Isolation and characterization of an uncoupler-resistant mutant of Methanothermobacter thermautotrophicus

A spontaneous mutant of Methanothermobacter thermautotrophicus resistant to the protonophorous uncoupler TCS was isolated. The mutant strain exhibited increased CH(4) formation and elevated level of ATPase activity under non-growing conditions. ATP synthesis driven by methanogenic electron transport as well as by potassium diffusion potential in the presence of either H(+) or Na(+) ions was markedly diminished in the mutant strain. An abundant membrane-associated protein complex with molecular mass approximately 670 kDa was detected in the mutant strain after native PAGE. The results indicate that TCS resistance in this mutant has arisen as a consequence of mutation(s) that affects a specific locus coding for an uncoupler binding protein(s) and/or modulate the activity of unidentified ATPase.

Biochemical characteristics of a mutant of the methanoarchaeon Methanothermobacter thermautotrophicus resistant to the protonophoric uncoupler TCS

In an attempt to more closely define a protein basis of differences in ATPase and ATP synthase activities in a mutant of the methanoarchaeon Methanothermobacter thermautotrophicus resistant to the protonophoric uncoupler TCS (3,3',4',5-tetrachlorosalicylanilide), the composition of membrane associated proteins from the wild-type and mutant strains has been compared. The uncoupler-resistance in the mutant strain was not accompanied by changes in a protein size or changes in the level of subunits A, B and c (proteolipid) of the A1A0-type ATPase-synthase. On the other hand, we revealed a 670-kDa membrane-associated protein complex that is abundantly present only in the mutant strain; it is composed of at least 5 different subunits of 95, 52, 42, 29 and 22 kDa.

Effect of Stryphnodendron adstringens (barbatimão) on energy metabolism in the rat liver

The action of a barbatimão extract on hepatic energy metabolism was investigated using isolated mitochondria and the perfused rat liver. In mitochondria the barbatimão extract inhibited respiration in the presence of ADP and succinate. Stimulation occurred, however, after ADP phosphorylation (state IV respiration). The ADP/O and respiratory control ratios were reduced. The activities of succinate-oxidase, NADH-oxidase and the oxidation of ascorbate were inhibited. The ATPase of intact mitochondria was stimulated, but the ATPases of uncoupled and disrupted mitochondria were inhibited. In perfused livers the extract caused stimulation of oxygen consumption, inhibition of gluconeogenesis and stimulation of glycolysis. Glucose release due to glycogenolysis was stimulated shortly after the introduction of the extract, but inhibition gradually developed as the infusion was continued. Apparently the barbatimão extract impairs the hepatic energy metabolism by three mechanisms: (1) uncoupling of oxidative phosphorylation, (2) inhibition of mitochondrial electron transport, and (3) inhibition of ATP-synthase.

Cycles of mitochondrial energization driven by the ultradian clock in a continuous culture of Saccharomyces cerevisiae

A continuous culture of Saccharomyces cerevisiae IFO 0233, growing with glucose as the major carbon and energy source, shows oscillations of respiration with a period of 48 min. Samples taken at maxima and minima indicate that (i) periodic changes do not occur as a result of carbon depletion, (ii) intrinsic differences in respiratory activity occur in washed organisms and (iii) a respiratory inhibitor accumulates during respiratory oscillations. Plasma membrane and inner mitochondrial membranes generate transmembrane electrochemical potentials; changes in these can be respectively assessed using anionic or cationic fluorophores. Thus flow cytometric analyses indicated that an oxonol dye [DiBAC(4)(3); bis(1,3-dibutylbarbituric acid)trimethine oxonol] was excluded from yeasts to a similar extent (in >98% of the population) at all stages, showing that the plasma membrane potential was maintained at a steady value. However, uptake of Rhodamine 123 was greatest at that phase characterized by a low respiratory rate. Addition of uncouplers of energy conservation [CCCP (m-chlorocarbonylcyanide phenylhydrazone) or S-13(5-chloro-3-t-butyl-2-chloro-4(1)-nitrosalicylanilide)] to the continuous cultures increased the respiration, but had only a transient effect on the period of the oscillation. Electron microscopy showed changes in mitochondrial ultrastructure during the respiratory oscillation. At low respiration the cristae were more clearly defined due to swelling of the matrix; this corresponds to the 'orthodox' conformation. When respiration was high the mitochondrial configuration was 'condensed'. It has been shown previously that a temperature-compensated ultradian clock operates in S. cerevisiae. It is proposed that mitochondria undergo cycles of energization in response to energetic demands driven by this ultradian clock output.

Biochemical evidence for transcytotic absorption of polyaspartamide from the rat lung: effects of temperature and metabolic inhibitors

Airway-to-perfusate polyhydroxyethylaspartamide (PHEA) absorption was studied in the isolated perfused rat lung at a reduced temperature and by the use of metabolic inhibitors, to kinetically clarify the mechanisms and cellular pathways of its active absorption. Fluorophore-labeled PHEA (F-PHEA; 7.4 kDa) was administered into the airways, and its absorption followed with time at 25 degrees C and in the presence of 2,4-dinitrophenol (DNP), ouabain (OUA), monensin (MON), and nocodazole (NOC). Across-dose absorption profiles were analyzed using a kinetic model incorporating active (V(max,P) and K(m,P)) and passive (k(a,P)) absorption from the pulmonary lung region alongside the competing, pulmonary-to-bronchial mucociliary escalator (k(E)). The model was validated at 25 degrees C and a lack of perturbation on the k(a,P) and k(E) values for passively absorbed solutes confirmed by studying the disposition of sodium fluorescein and 4.4 kDa fluorescein isothiocyanate-labeled dextran. F-PHEA absorption was significantly suppressed at 25 degrees C, compared with 37 degrees C, because of a significant decrease in the value of the maximum rate of active absorption, V(max,P) (4.37 --> 0.67 microg/min; p < 0.05), whereas the carrier-affinity term, K(m,P), was statistically unchanged. F-PHEA's active absorption was also significantly inhibited by DNP (> or =0.5 mM), OUA (> or =50 microM), MON (> or =10 microM), and NOC (> or =1 microM), whereas these inhibitors had no significant effect on the values for k(a,P) and k(E). Thus, F-PHEA's pulmonary active absorption in the rat lung was temperature- and adenosine 5'-triphosphate-derived intracellular energy-dependent (DNP and OUA inhibition) and apparently mediated via transcytosis through cytoplasmic endosomes and microtubules (MON and NOC inhibition).

Inhibition of oxygen consumption by pentachlorophenol and tetrachloroguaiacol in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) were exposed for 24 h to concentrations representing 100, 50 and 25% of the 96 h-LC50 of pentachlorophenol (PCP) or tetrachloroguaiacol (TCG), and their oxygen consumption, cardiac output, heart rate and stroke volume were measured at regular intervals. Oxygen consumption either remained stable at basal levels (PCP), or increased to 130% of basal levels (TCG) when fish were exposed to the 96 h-LC50 of each chemical. However, oxygen consumption decreased to about 50-60% of basal levels when fish were exposed to concentrations of PCP or TCG representing 50 and 25% of the 96 h-LC50. This decrease in oxygen consumption did not appear to affect cardiac function since cardiac output, heart rate and stroke volume remained stable. PCP is best known for its capacity to uncouple oxidative phosphorylation and increase oxygen consumption. However, this study showed that it can also decrease oxygen consumption, and that the effects of PCP and TCG on fish metabolism are similar.

Probenecid interferes with renal oxidative metabolism: a potential pitfall in its use as an inhibitor of drug transport

The anionic drug probenecid has been traditionally used as an inhibitor of renal organic anion transport. More recently the drug was found to inhibit organic cation transport as well, and it is used to retain intracellularly loaded fluorophores. In these investigations it is implicitly assumed that probenecid performs its activity through competition for transport. Here we studied the possibility that probenecid provokes its effect through inhibition of cellular oxidative metabolism. Oxygen consumption was measured in isolated rat kidney cortex mitochondria. At concentrations of 1 mM or higher, probenecid increased the resting state (state 4) and decreased the ADP-stimulated respiration (state 3). A complete loss in respiratory control was observed at 10 mM probenecid. After incubating isolated rat kidney proximal tubular cells (PTC) for 30 min with probenecid a concentration-dependent reduction in ATP content was observed, which was significant at concentrations of 1 mM and higher. Using digital image fluorescence microscopy the membrane potential in PTC was measured with bisoxonol. The mitochondrial effects of probenecid were paralleled by a depolarization of the plasma membrane, immediately after drug addition. All events are likely to be a result of membrane disordering due to the lipophilic character of probenecid, and may explain, at least in part, the various inhibitory effects found for the drug. We recommend to be cautious with applying probenecid in cellular research.

Insight into the uncoupling mechanism of sarcoplasmic reticulum ATPase using the phosphorylating substrate UTP

Ca(2+) transport and UTP hydrolysis catalyzed by sarcoplasmic reticulum Ca(2+)-ATPase from skeletal muscle was studied. A passive Ca(2+) load inside microsomal vesicles clearly decreased the net uptake rate and the final accumulation of Ca(2+) but not the UTP hydrolysis rate, causing energy uncoupling. In the absence of passive leak, the Ca(2+)/P(i) coupling ratio was 0.7-0.8. UTP hydrolysis did not maintain a rapid component of Ca(2+) exchange between the cytoplasmic and lumenal compartments as occurs with ATP. The uncoupling process in the presence of UTP is associated with: (i) the absence of a steady state accumulation of ADP-insensitive phosphoenzyme; (ii) the cytoplasmic dissociation of Ca(2+) bound to the ADP-sensitive phosphoenzyme; and (iii) the absence of enzyme inhibition by cyclopiazonic acid. All these characteristics confirm the lack of enzyme conformations with low Ca(2+) affinity and point to the existence of an uncoupling mechanism mediated by a phosphorylated form of the enzyme. Suboptimal coupling values can be explained in molecular terms by the proposed functional model.

Quantitative structure-activity relationships for the toxicity of chlorophenols to mammalian submitochondrial particles

The toxicity of a series of chlorophenols, determined by a short-term in vitro assay utilizing mammalian submitochondrial particles, was related to the physicochemical and structural properties of these compounds. Quantitative Structure-Activity Relationships were defined by correlating EC50 values with six molecular descriptors, chosen to represent lipophilic, electronic and steric effects: the n-octanol/water partition coefficient (log Kow), the constant of Hammett (sigma sigma), the acid dissociation constant (pKa), the first order valence molecular connectivity index (1 chi v), the perimeter of the efficacious section (sigma D) and the melting point (m.p.). The results of regression analysis showed that log Kow is the most successful descriptor, indicating that the ability of chlorophenols to partition into the lipid bilayer of the mitochondrial membrane has an important role in determining their toxic effects. These results are consistent with a molecular mechanism of uncoupling action based on the chemiosmotic theory and on the protonophoric properties of chlorophenols. The quality of the QSAR models confirms the suitability of the SMP assay as a short-term prediction tool for aquatic toxicity of environmental pollutants acting on respiratory functions.

Effect of MI-D, a new mesoionic compound, on energy-linked functions of rat liver mitochondria

MI-D (4-phenyl-5-(4-nitro-cinnamoyl)-1,3,4-thiadiazolium-2-phenylami ne chloride), a new mesoionic compound, depressed the phosphorylation efficiency of liver mitochondria as deduced from an accentuated decrease of the respiratory control coefficient and ADP/O ratio. Analysis of segments of the respiratory chain suggested that the MI-D inhibition site is further on than complex I and between complexes II and III. The transmembrane electrical potential (delta psi) was collapsed dependent on MI-D concentration. ATPase activity was dramatically increased by MI-D in intact mitochondria, but inhibited in carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP)-uncoupled mitochondria. These results suggest that MI-D acts as an uncoupler agent, a property closely related to its structural characteristics.

Flux-force relationships in intact cells: a helpful tool for understanding the mechanism of oxidative phosphorylation alterations?

On isolated mitochondria, numerous studies of the relationships between fluxes and their associated forces have led to the description of some properties of the oxidative phosphorylation pathway. However whether such an approach can be applied to understanding the actual situation in intact living cells needs further consideration. In this study on isolated hepatocytes, we describe the dependence of the respiratory rate on the three thermodynamic forces linked to oxidative phosphorylation (i.e. the redox span over the respiratory chain, the electrical potential difference across the inner mitochondrial membrane and the free energy of ATP synthesis reaction). Even if this description is phenomenological and some objections may be raised regarding the relevance of such a bulk-phase force estimation, we present some results showing that the study of flux-force relationships in intact cells may be a helpful approach for understanding the mechanisms by which oxidative phosphorylation activity is changed.

Effects of the nonsteroidal anti-inflammatory drug piroxicam on rat liver mitochondria

1. The effects of piroxicam, a nonsteroidal anti-inflammatory drug, on rat liver mitochondria were investigated in order to obtain direct evidence about a possible uncoupling effect, as suggested by a previous work with the perfused rat liver. 2. Piroxicam increased respiration in the absence of exogenous ADP and decreased respiration in the presence of exogenous ADP, the ADP/O ratios and the respiratory control ratios. 3. The ATPase activity of intact mitochondria was increased by piroxicam. With 2,4-dinitrophenol uncoupled mitochondria, inhibition was observed. The ATPase activity of freeze-thawing disrupted mitochondria was insensitive to piroxicam. 4. Swelling driven by the oxidation of several substrates and safranine uptake induced by succinate oxidation were inhibited. 5. The results of this work represent a direct evidence that piroxicam acts as an uncoupler, thus, decreasing mitochondrial ATP generation.

Octanoate affects 2,4-dinitrophenol uncoupling in intact isolated rat hepatocytes

When intact isolated rat hepatocytes, either incubated or perifused, were uncoupled by 2,4-dinitrophenol, we found that the effect on glucose and lactate+pyruvate fluxes, cytosolic and mitochondrial redox states and ATP/ADP ratios were dependent on the nature of the exogenous substrate added. 2,4-Dinitrophenol addition (0.25 mmol/l) to cells perifused with dihydroxyacetone (10 mmol/l) resulted in a modest and transient activation of oxygen uptake accompanied by a surprising rise in lactate/pyruvate ratio indicating an increase in the cytosolic NADH/NAD+ ratio. In addition, such uncoupling, fully abolished glucose production, enhanced lactate+pyruvate flux, and strongly decreased cytosolic and mitochondrial ATP/ADP ratios. In these steady-state conditions, further addition of octanoate (0.4 mmol/l) induced a large and sustained enhancement of respiration with a concomitant decrease in the lactate/pyruvate ratio, whereas glucose flux was restored to some extent and cytosolic and mitochondrial ATP/ADP ratios increased. Inhibition of the malate-aspartate shuttle by the transaminase inhibitor aminooxyacetate (0.3 mmol/l) did not modify the effect of 2,4-dinitrophenol with dihydroxyacetone alone whereas it decreased the maximal stimulation of oxygen uptake after octanoate addition. In view of these results we propose the following conclusions. The uncoupling of intact cells by 2,4-dinitrophenol inhibits the translocation of reducing equivalents into the mitochondrial matrix probably by impairing the malate-aspartate shuttle. This explains the increase in the cytosolic NADH/NAD+ ratio and the transient activation of respiration with dihydroxyacetone. Fatty acid addition to cells uncoupled with 2,4-dinitrophenol appears to restore a mitochondrial membrane potential, probably by providing the respiratory chain with reduced cofactors directly in the matrix, thus allowing the transfer of reducing equivalents across the mitochondrial membrane. The restoration, to some extent, of a protonmotive force to uncoupled cells by fatty acid addition is also supported by an increase in ATP synthesis as evidenced by a glucose synthesis with dihydroxyacetone as gluconeogenic substrate.

Understanding cellular responses to toxic agents: a model for mechanism-choice in bacterial metal resistance

Bacterial resistances to metals are heterogeneous in both their genetic and biochemical bases. Metal resistance may be chromosomally-, plasmid- or transposon-encoded, and one or more genes may be involved: at the biochemical level at least six different mechanisms are responsible for resistance. Various types of resistance mechanisms can occur singly or in combination and for a particular metal different mechanisms of resistance can occur in the same species. To understand better the diverse responses of bacteria to metal ion challenge we have constructed a qualitative model for the selection of metal resistance in bacteria. How a bacterium becomes resistant to a particular metal depends on the number and location of cellular components sensitive to the specific metal ion. Other important selective factors include the nature of the uptake systems for the metal, the role and interactions of the metal in the normal metabolism of the cell and the availability of plasmid (or transposon) encoded resistance mechanisms. The selection model presented is based on the interaction of these factors and allows predictions to be made about the evolution of metal resistance in bacterial populations. It also allows prediction of the genetic basis and of mechanisms of resistance which are in substantial agreement with those in well-documented populations. The interaction of, and selection for resistance to, toxic substances in addition to metals, such as antibiotics and toxic analogues, involve similar principles to those concerning metals. Potentially, models for selection of resistance to any substance can be derived using this approach.

Effect of Tordon 2,4-D 64/240 triethanolamine BR on the energy metabolism of rat liver mitochondria

Tordon herbicide, which is a mixture of 4-amino-3,5,6-trichloropicolinic acid (picloram) and 2,4-dichlorophenoxyacetic acid (2,4-D), depresses the phosphorylation efficiency of the rat liver mitochondria, as inferred from the decrease of the respiratory control coefficient and the ADP/O ratios when NAD(+)-dependent substrates were used; NADH oxidase and NADH cytochrome c reductase were also inhibited, without any effect on the other enzymatic complexes of the respiratory chain. Tordon (66.2 nmol picloram + 270 nmol 2,4-D mg-1 protein) affected the amplitude of swelling induced by glutamate, succinate, (N,N,N',N'-tetramethyl-p-phenyldiamine + sodium ascorbate and ATP. These results characterize an interaction of Tordon with complex I of the respiratory chain and also a partial collapse of the proton motive force of the mitochondrial inner membrane without affecting its elasticity.

Transport, distribution space and intracellular concentration of the anti-inflammatory drug niflumic acid in the perfused rat liver

Transport and distribution space of niflumic acid in the perfused rat liver were investigated employing the multiple-indicator dilution technique with constant infusion of the drug (step input). Niflumic acid permeated the cell membrane in both directions at very high rates and its distribution in the cellular space was flow-limited; at least at 37 degrees, the rates of influx and efflux could not be measured. Dissociation of the niflumic acid-albumin complex also occurred at very high rates. The apparent space of distribution of niflumic acid in the liver depended on the concentration of the drug and varied between 4.37 (1 mM) and 43.5 (10 microM) times the water space; even with 90% extracellular binding to albumin, the apparent space of distribution of niflumic acid was 5.1 times greater than the water space. The high apparent spaces of distribution reflected the high intracellular concentrations. The ratio of intracellular bound plus free concentration to the extracellular bound plus free concentration (Ci/Ce) varied between 6.62 (1 mM portal niflumic acid) and 71.0 (10 microM portal niflumic acid). Metabolic transformation depended on the concentration of the free form. Intracellular binding is probably the major reason for the high concentration of the drug in the hepatic tissue.

Respiratory control induced by ATP in human term placental mitochondria

Oxygen uptake in human placental mitochondria was stimulated by ATP addition. ATP-induced respiration was supported by malate, alpha-keto glutarate, and succinate, and inhibited by oligomycin and carboxytractyloside. This phenomenon was not caused by contamination with unspecific phosphatases or alkaline phosphatase, since NaF, L-phenyl alanine, or P1, P5-di-(adenosine-5') pentaphosphate failed to inhibit oxygen uptake induced by ATP. The stimulation of respiration was caused by an ATPase activity tightly bound to mitochondria, which yields ADP that is responsible for the oxygen uptake. The stimulation was not an uncoupling effect because ATP addition produced a transition between state 3 and 4 of respiration, indicating that ATP was not released from mitochondria.

Aneurysm of the azygos pericallosal artery. One case

The Authors describe a case of aneurysmal rupture of the azygos pericallosal artery, a variant of the anterior cerebral artery. The association between aneurysm and this anatomical anomaly is of interest because of its rarity and clinical-therapeutic implications.

Characterization of a mitochondrial inorganic pyrophosphatase in Saccharomyces cerevisiae

We have studied a mitochondrial inorganic pyrophosphatase (PPase) in the yeast Saccharomyces cerevisiae. The uncoupler FCCP (carbonyl cyanide p-trifluoromethoxyphenylhydrazone) and the ionophores valinomycin and nigericin stimulate the PPase activity of repeatedly washed yeast mitochondria 2-3-fold. We have previously cloned a yeast gene, PPA2, encoding the catalytic subunit of a mitochondrial PPase. Uncouplers stimulate the PPase activity several-fold in mitochondria from both cells that overexpress PPA2 from a high copy number plasmid and cells with normal expression. These results indicate that the PPA2 polypeptide functions as an energy linked and membrane associated PPase. The stimulation of mitochondrial PPase activity by FCCP, but not by valinomycin and nigericin, was greatly enhanced by the presence of DTT. The antibiotics Dio-9, equisetin and the F0F1-ATPase inhibitor oligomycin also increase mitochondrial PPase activity several fold. This stimulation is much higher, whereas basal PPase activity is lower, in isotonic than in hypotonic solution, which indicates that intact membranes are a prerequisite for maximal effects.