Enhancing Escherichia coli abiotic stress resistance through ornithine lipid formation

Escherichia coli is a common host for biotechnology and synthetic biology applications. During growth and fermentation, the microbes are often exposed to stress conditions, such as variations in pH or solvent concentrations. Bacterial membranes play a key role in response to abiotic stresses. Ornithine lipids (OLs) are a group of membrane lipids whose presence and synthesis have been related to stress resistance in bacteria. We wondered if this stress resistance could be transferred to bacteria not encoding the capacity to form OLs in their genome, such as E. coli. In this study, we engineered different E. coli strains to produce unmodified OLs and hydroxylated OLs by expressing the synthetic operon olsFC. Our results showed that OL formation improved pH resistance and increased biomass under phosphate limitation. Transcriptome analysis revealed that OL-forming strains differentially expressed stress- and membrane-related genes. OL-producing strains also showed better growth in the presence of the ionophore carbonyl cyanide 3-chlorophenylhydrazone (CCCP), suggesting reduced proton leakiness in OL-producing strains. Furthermore, our engineered strains showed improved heterologous violacein production at phosphate limitation and also at low pH. Overall, this study demonstrates the potential of engineering the E. coli membrane composition for constructing robust hosts with an increased abiotic stress resistance for biotechnology and synthetic biology applications. KEY POINTS: • Ornithine lipid production in E. coli increases biomass yield under phosphate limitation. • Engineered strains show an enhanced production phenotype under low pH stress. • Transcriptome analysis and CCCP experiments revealed reduced proton leakage.

Divergent Roles of Escherichia Coli Encoded Lon Protease in Imparting Resistance to Uncouplers of Oxidative Phosphorylation: Roles of marA, rob, soxS and acrB

Uncouplers of oxidative phosphorylation dissipate the proton gradient, causing lower ATP production. Bacteria encounter several non-classical uncouplers in the environment, leading to stress-induced adaptations. Here, we addressed the molecular mechanisms responsible for the effects of uncouplers in Escherichia coli. The expression and functions of genes involved in phenotypic antibiotic resistance were studied using three compounds: two strong uncouplers, i.e., Carbonyl cyanide m-chlorophenyl hydrazone (CCCP) and 2,4-Dinitrophenol (DNP), and one moderate uncoupler, i.e., Sodium salicylate (NaSal). Quantitative expression studies demonstrated induction of transcripts encoding marA, soxS and acrB with NaSal and DNP, but not CCCP. Since MarA and SoxS are degraded by the Lon protease, we investigated the roles of Lon using a lon-deficient strain (Δlon). Compared to the wild-type strain, Δlon shows compromised growth upon exposure to NaSal or 2, 4-DNP. This sensitivity is dependent on marA but not rob and soxS. On the other hand, the Δlon strain shows enhanced growth in the presence of CCCP, which is dependent on acrB. Interestingly, NaSal and 2,4-DNP, but not CCCP, induce resistance to antibiotics, such as ciprofloxacin and tetracycline. This study addresses the effects of uncouplers and the roles of genes involved during bacterial growth and phenotypic antibiotic resistance. Strong uncouplers are often used to treat wastewater, and these results shed light on the possible mechanisms by which bacteria respond to uncouplers. Also, the rampant usage of some uncouplers to treat wastewater may lead to the development of antibiotic resistance.

Varicella zoster virus glycoprotein E facilitates PINK1/Parkin-mediated mitophagy to evade STING and MAVS-mediated antiviral innate immunity

Viruses have evolved to control mitochondrial quality and content to facilitate viral replication. Mitophagy is a selective autophagy, in which the damaged or unnecessary mitochondria are removed, and thus considered an essential mechanism for mitochondrial quality control. Although mitophagy manipulation by several RNA viruses has recently been reported, the effect of mitophagy regulation by varicella zoster virus (VZV) remains to be fully determined. In this study, we showed that dynamin-related protein-1 (DRP1)-mediated mitochondrial fission and subsequent PINK1/Parkin-dependent mitophagy were triggered during VZV infection, facilitating VZV replication. In addition, VZV glycoprotein E (gE) promoted PINK1/Parkin-mediated mitophagy by interacting with LC3 and upregulating mitochondrial reactive oxygen species. Importantly, VZV gE inhibited MAVS oligomerization and STING translocation to disrupt MAVS- and STING-mediated interferon (IFN) responses, and PINK1/Parkin-mediated mitophagy was required for VZV gE-mediated inhibition of IFN production. Similarly, carbonyl cyanide m-chlorophenyl hydrazone (CCCP)-mediated mitophagy induction led to increased VZV replication but attenuated IFN production in a three-dimensional human skin organ culture model. Our results provide new insights into the immune evasion mechanism of VZV gE via PINK1/Parkin-dependent mitophagy.

Cultured Rat Hippocampal Neurons Exposed to the Mitochondrial Uncoupler Carbonyl Cyanide Chlorophenylhydrazone Undergo a Rapid, Presenilin-Dependent Change in Neuronal Properties

Presenilin 1 (PS1) is a transmembrane proteolytic subunit of γ-secretase that cleaves amyloid precursor proteins. Mutations in PS1 (mPS1) are associated with early-onset familial Alzheimer's disease (AD). The link between mutated PS1, mitochondrial calcium regulation, and AD has been studied extensively in different test systems. Despite the wide-ranging role of mPS1 in AD, there is a paucity of information on the link between PS1 and neuronal cell death, a hallmark of AD. In the present study, we employed the selective mitochondrial uncoupler carbonyl cyanide chlorophenylhydrazone (CCCP) and compared the reactivity of mPS1-transfected cultured rat hippocampal neurons with PS1 and control neurons in a situation of impaired mitochondrial functions. CCCP causes a slow rise in cytosolic and mitochondrial calcium in all three groups of neurons, with the mPS1 neurons demonstrating a faster rise. Consequently, mPS1 neurons were depolarized by CCCP and measured with TMRM, a mitochondrial voltage indicator, more than the other two groups. Morphologically, CCCP produced more filopodia in mPS1 neurons than in the other two groups, which were similarly affected by the drug. Finally, mPS1 transfected neurons tended to die from prolonged exposure to CCCP sooner than the other groups, indicating an increase in vulnerability associated with a lower ability to regulate excess cytosolic calcium.

Where Are the Children? A Thematic Analysis of State, Territory, and Tribal Organization Comprehensive Cancer Control Plans

BACKGROUND

The Center for Disease Control's Comprehensive Cancer Control Program (CCCP) funds initiatives in fifty states, the District of Columbia, seven U.S. territories, and seven tribal organizations to prevent and control cancer. These initiatives influence policy, care, research, and advocacy for cancer treatment. We performed an analysis of CCCP plans for states, U.S. territories, and tribal organizations to understand the extent of inclusion of pediatric cancer care.

METHODS

We conducted a thematic and quantitative analysis of CCCP plans for states, U.S. territories, and tribal organizations. Plans were assessed by two reviewers and scored for discussion of cancer prevention, risk factors, early detection and screening, treatment and innovation, access, barriers to care, and survivorship in childhood cancer.

RESULTS

Plans from fifty states, the District of Columbia, seven territories, seven tribal organizations, and one Pacific Regional (USAPI) plan were reviewed, for a total of sixty-six plans. Up-to-date CCCP plans were available through the CDC or state websites for 74% of states, 57% of territories, and 71% of tribal organizations; older plans were available for all groups without up-to-date CCCP plans. While all plans referenced children, most did so in the context of childhood exposures influencing adult cancer risks (e.g., sun, tobacco, HPV). Few plans contained a section dedicated to childhood cancer (30% states, 14.3% territories, 14.3% tribes). A minority of plans specifically discussed early detection and screening (14% states, 0% territories, 14.3% tribes), treatment and innovation (32% states, 0% territories, 28.6% tribes), access to cancer care (38% states, 28.6% territories, 28.6% tribes), reducing barriers to cancer care (28% states, 42.9% territories, 28.6% tribes), and pediatric cancer survivorship (42% states, 0% territories, 28.6% tribes).

CONCLUSIONS

Promoting inclusion of pediatric cancer in CCPs will help to standardize pediatric cancer care, eliminate treatment disparities across state lines, and allow for comprehensive understanding of pediatric oncology.

LEVEL OF EVIDENCE

Level IV.

TRIM28 promotes porcine epidemic diarrhea virus replication by mitophagy-mediated inhibition of the JAK-STAT1 pathway

Porcine epidemic diarrhea virus (PEDV) infection causes immunosuppression and clinical symptoms such as vomiting, watery diarrhea, dehydration, and even death in piglets. TRIM28, an E3 ubiquitin ligase, is involved in the regulation of autophagy. However, the role of TRIM28 in PEDV infection is unknown. This study aimed to determine whether TRIM28 acts as a host factor for PEDV immune escape. We found that depletion of TRIM28 inhibited PEDV replication, whereas overexpression of TRIM28 promoted the viral replication in host cells. Furthermore, knockdown of TRIM28 reversed PEDV-induced downregulation of the JAK/STAT1 pathway. Treatment with the mitophagic activator carbonyl cyanide 3-chlorophenylhydrazone (CCCP) attenuated the activating effect of TRIM28 depletion on the expression of the STAT1 pathway-related proteins. Treatment with CCCP also reduced the nuclear translocation of pSTAT1. Moreover, TRIM28, via its RING domain, interacted with PEDV N. Overexpression of TRIM28 induced mitophagy, which could be enhanced by co-expression with PEDV N. The results indicate that PEDV infection upregulates the expression of TRIM28, which induces mitophagy, leading to inhibition of the JAK-STAT1 pathway. This research unveils a new mechanism by which PEDV can hijack host cellular TRIM28 to promote its own replication.

Multidrug Efflux System-mediated resistance in Staphylococcus aureus under a One Health approach

The aim of the study was to track the spread of antimicrobial resistance among the different sectors of One Health through the detection of Multidrug-Efflux-System in multidrug-resistant Staphylococcus aureus isolates. Multidrug-resistant (MDR) and methicillin-resistant (MRSA) S. aureus isolates were selected: 25 of human, one of animal and eight of food origin. The efflux system genes norA, norB, norC, LmrS, tet38 and msrA were screened by PCR. The activity of the efflux systems was determined by the minimum inhibitory concentration (MIC) of tetracycline and ciprofloxacin in the presence and absence of CCCP and in the quantification of ethidium bromide efflux. Furthermore, biofilm formation was determined in the presence and absence of the CCCP. The molecular epidemiology of the isolates was traced with the aid of PFGE. The gene norC was the most prevalent, detected in all isolates and msrA was the least prevalent, detected in only two isolates from humans. There was no difference in the MICs of tetracycline and ciprofloxacin in the presence of CCCP, but 55.9% of isolates showed ethidium bromide efflux. The presence of CCCP decreased the biofilm formation. Regarding the molecular epidemiology, in three clusters was a mixture of the isolates from different origins. Therefore, S. aureus MDR with active multidrug efflux systems are circulating between One Health domains and it is necessary to consider strategies to decrease this circulation in order to prevent the dissemination of resistance mediated by MES.

Gastric Neuroendocrine Tumor Treatment and Survival Outcome Depends on Facility Type

BACKGROUND

Gastric neuroendocrine tumors (gNETs) are rare cancers for which surgery may improve survival. We aim to determine if facility type affects treatment and survival outcomes.

METHODS

The NCDB was queried for patients with gNET from 2004-2016 and stratified into Academic/Research Program (ARP), Community Cancer Program (CCP), Comprehensive Community Cancer Program (CCCP), or Integrated Network Cancer Program (INCP). Overall survival along with clinical and demographic features was compared.

RESULTS

Median survival was improved in patients treated at an academic program: 137.3 months versus 88.0, 96.3, and 100.2 for CCP, CCCP, INCP, respectively (P < .0001). Patients treated at academic centers were more likely to have surgery (64.2% vs 59.1%, 57.5%, 51.4%, P < .0001). After propensity matching for age, race, grade, stage, insurance status, and comorbidity score, survival benefit from treatment at an academic center remained (P = .03), particularly for patients undergoing surgery (P < .0001) and chemotherapy (P = .04).

CONCLUSION

Patients with gNET treated at an academic hospital had improved median survival after propensity matching and may benefit from treatment at academic rather than community medical centers.

Exposure of Cultured Hippocampal Neurons to the Mitochondrial Uncoupler Carbonyl Cyanide Chlorophenylhydrazone Induces a Rapid Growth of Dendritic Processes

A major route for the influx of calcium ions into neurons uses the STIM-Orai1 voltage-independent channel. Once cytosolic calcium ([Ca2+]i) elevates, it activates mitochondrial and endoplasmic calcium stores to affect downstream molecular pathways. In the present study, we employed a novel drug, carbonyl cyanide chlorophenylhydrazone (CCCP), a mitochondrial uncoupler, to explore the role of mitochondria in cultured neuronal morphology. CCCP caused a sustained elevation of [Ca2+]i and, quite surprisingly, a massive increase in the density of dendritic filopodia and spines in the affected neurons. This morphological change can be prevented in cultures exposed to a calcium-free medium, Orai1 antagonist 2APB, or cells transfected with a mutant Orai1 plasmid. It is suggested that CCCP activates mitochondria through the influx of calcium to cause rapid growth of dendritic processes.

AZD5438 a GSK-3a/b and CDK inhibitor is antiapoptotic modulates mitochondrial activity and protects human neurons from mitochondrial toxins

We previously reported that kenpaullone, which inhibits GSK-3a/b and CDKs inhibited CCCP mediated mitochondrial depolarisation and augments the mitochondrial network. To investigate the actions of this class of drug further, we compared the ability of kenpaullone, alsterpaullone, 1-azakenapaullone, AZD5438, AT7519 (CDK and GSK-3a/b inhibitors) and dexpramipexole and olesoxime (mitochondrial permeability transition pore inhibitors) to prevent CCCP mediated mitochondrial depolarisation and found that AZD5438 and AT7519, were the most effective. Furthermore, treatment with AZD5438 alone increased the complexity of the mitochondrial network. We also found that AZD5438 prevented the rotenone induced decrease in PGC-1alpha and TOM20 levels and that it mediated powerful anti-apoptotic effects and promoted glycolytic respiration. Importantly, experiments in human iPSC derived cortical and midbrain neurons showed AZD5438 mediated significant protective effects, preventing the neuronal cell death, and collapse in the neurite and mitochondrial network associated with rotenone treatment. These results suggest drugs that target GSK-3a/b and CDKs should be developed and assessed further as they may have significant therapeutic potential.

[Effects of four efflux pump inhibitors on the activities of clarithromycin against Mycobacterium abscessus]

Objective: To detect the effects of four efflux pump inhibitors on the minimum inhibitory concentration of clarithromycin (CLA) against Mycobacterium abscessus (M. abscessus) in vitro, and to explore the role of efflux pump in CLA resistance of M. abscessus. Methods: Four frequently-used efflux pump inhibitors (Carbonyl Cyanide 3-chlorophenylhydrazone, CCCP, N, N'-dicyclohexylcarbodiimide, DCC, Verapamil, VP, Reserpine, RSP) were evaluated in this study. The minimum inhibitory concentration (MIC) values of clarithromycin against M. abscessus reference strain and 60 clinical strains with or without efflux pump inhibitors were detected by Alamar Blue method. Sequence analysis of erm(41) and rrl genes known to be associated with CLA resistance in M. abscessus was performed to analyze the correlation between the effect of efflux pump inhibitors on MIC and mutation of resistance-related genes. Results: CCCP, DCC, VP and RSP could reduce the MIC of M. abscessus to CLA, and the effect of RSP was weaker than the other three efflux pump inhibitors. Among the sixty M. abscessus clinical strains, ten strains were resistant to clarithromycin, seven of which had rrl gene mutation. The CLA resistance rate of smooth phenotype isolates was higher than that of rough phenotype isolates. At 3 day of clarithromycin incubation, the MICs of resistant strains were all reduced by efflux pump inhibitors. Compared with the strains with rrl gene mutation, efflux pump inhibitors had a greater effect on the strains without rrl gene mutation. At 14 day of clarithromycin incubation, 83% of M. abscessus subsp. abscessus, were induced to be resistant, and all of them were T28 sequence type of erm(41). With the occurrence of induced drug resistance, the effect of efflux pump inhibitor on CLA MIC decreased. Efflux pump inhibitors had no statistically significant diffence in the effect of effcux pump inhibitors on CLA MIC levels in different phenotypes of isolates. Conclusions: Efflux pump is involved in the resistance process of M. abscessus to CLA. Efflux pump inhibitors reduce the drug resistance to clarithromycin against M. abscessus in different degrees. The use of efflux pump inhibitors may provide a new way to alleviate the drug resistance of M. abscessus.

CHCHD2 and CHCHD10 regulate mitochondrial dynamics and integrated stress response

Mitochondrial dysfunction is becoming one of the main pathology factors involved in the etiology of neurological disorders. Recently, mutations of the coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2) and 10 (CHCHD10) which encode two homologous proteins that belong to the mitochondrial CHCH domain protein family, are linked to Parkinson's disease and amyotrophic lateral sclerosis (ALS)/frontotemporal dementia (FTD), respectively. However, the physiological and pathological roles of these twin proteins have not been well elaborated. Here, we show that, in physiological conditions, CHCHD2 and CHCHD10 interact with OMA1 and suppress its enzyme activity, which not only restrains the initiation of the mitochondrial integrated response stress (mtISR), but also suppresses the processing of OPA1 for mitochondrial fusion. Further, during mitochondria stress-induced by carbonyl cyanide m-chlorophenylhydrazone (CCCP) treatment, CHCHD2 and CHCHD10 translocate to the cytosol and interacte with eIF2a, which attenuates mtISR overactivation by suppressing eIF2a phosphorylation and its downstream response. As such, knockdown of CHCHD2 and CHCHD10 triggers mitochondrial ISR, and such cellular response is enhanced by CCCP treatment. Therefore, our findings demonstrate the first "mtISR suppressor" localized in mitochondria for regulating stress responses in mammalian cells, which has a profound pathological impact on the CHCH2/CHCH10-linked neurodegenerative disorder.

Mitochondrial modulation-induced activation of vagal sensory neuronal subsets by antimycin A, but not CCCP or rotenone, correlates with mitochondrial superoxide production

Inflammation causes nociceptive sensory neuron activation, evoking debilitating symptoms and reflexes. Inflammatory signaling pathways are capable of modulating mitochondrial function, resulting in reactive oxygen species (ROS) production, mitochondrial depolarization and calcium release. Previously we showed that mitochondrial modulation with antimycin A, a complex III inhibitor, selectively stimulated nociceptive bronchopulmonary C-fibers via the activation of transient receptor potential (TRP) ankyrin 1 (A1) and vanilloid 1 (V1) cation channels. TRPA1 is ROS-sensitive, but there is little evidence that TRPV1 is activated by ROS. Here, we used dual imaging of dissociated vagal neurons to investigate the correlation of mitochondrial superoxide production (mitoSOX) or mitochondrial depolarization (JC-1) with cytosolic calcium (Fura-2AM), following mitochondrial modulation by antimycin A, rotenone (complex I inhibitor) and carbonyl cyanide m-chlorophenyl hydrazone (CCCP, mitochondrial uncoupling agent). Mitochondrial modulation by all agents selectively increased cytosolic calcium in a subset of TRPA1/TRPV1-expressing (A1/V1+) neurons. There was a significant correlation between antimycin A-induced calcium responses and mitochondrial superoxide in wild-type 'responding' A1/V1+ neurons, which was eliminated in TRPA1-/- neurons, but not TRPV1-/- neurons. Nevertheless, antimycin A-induced superoxide production did not always increase calcium in A1/V1+ neurons, suggesting a critical role of an unknown factor. CCCP caused both superoxide production and mitochondrial depolarization but neither correlated with calcium fluxes in A1/V1+ neurons. Rotenone-induced calcium responses in 'responding' A1/V1+ neurons correlated with mitochondrial depolarization but not superoxide production. Our data are consistent with the hypothesis that mitochondrial dysfunction causes calcium fluxes in a subset of A1/V1+ neurons via ROS-dependent and ROS-independent mechanisms.

Farnesol, a potential efflux pump inhibitor in Mycobacterium smegmatis

The active multidrug efflux pump (EP) has been described as one of the mechanisms involved in the natural drug resistance of bacteria, such as mycobacteria. As a result, the development of efflux pumps inhibitors (EPIs) is an important topic. In this study, a checkerboard synergy assay indicated that farnesol both decreased the minimum inhibitory concentration (MIC) of ethidium bromide (EtBr) 8-fold against Mycobacterium smegmatis (M. smegmatis) mc²155 ATCC 700084 when incorporated at a concentration of 32 μg/mL (FICI = 0.625) and decreased MIC 4-fold at 16 μg/mL (FICI = 0.375). Farnesol also showed synergism when combined with rifampicin. A real-time 96-well plate fluorometric method was used to assess the ability of farnesol to inhibit EPs in comparison withfour positive EPIs: chlorpromazine, reserpine, verapamil, and carbonyl cyanide m-chlorophenylhydrazone (CCCP). Farnesol significantly enhanced the accumulation of EtBr and decreased the efflux of EtBr in M. smegmatis; these results suggest that farnesol acts as an inhibitor of mycobacterial efflux pumps.

Calcium ionophore A23187 action on cardiac myocytes is accompanied by enhanced production of reactive oxygen species

We show that rat neonatal cardiac myocytes exposed to 1 micromol/l of the calcium ionophore A23187 respond with an enhanced production of reactive oxygen species (ROS). This dose is not cytotoxic to the myocytes. A higher concentration (10 micromol/l) evokes less ROS production and is significantly cytotoxic 24 h after exposure, but not immediately after removal of the A23187, when ROS are measured. Both cell death and the decrease in mitochondrial potential are only partially sensitive to MPT inhibitor cyclosporin A. Experiments performed to elucidate the sources of ROS included use of the nitric oxide synthase (NOS) inhibitor L-NAME; NOS involvement was excluded. Experiments with the oxidative phosphorylation uncoupler CCCP revealed that mitochondria are at least partially responsible for the observed effect. Further studies with cyclooxygenase (COX) and lipoxygenase (LOX) inhibitors (indomethacin and MK886, respectively) showed that these enzymes could also be sources of ROS when the calcium level is elevated. Their effect appeared to be independent of phospholipase A(2) inhibition, suggesting that COX and LOX stimulation is not due to elevated substrate (arachidonic acid) concentration but rather to a direct effect of calcium.

Binding, Aggregation and Photochemical Properties of Methylene Blue in Mitochondrial Suspensions

Methylene Blue (MB) has well-established photochemical properties and has been used in a variety of photochemical applications including photodynamic therapy. Despite the fact that most of MB's cytotoxic effects in cells are attributed to mitochondrial damage, the interactions of this dye with mitochondria and the consequent effects on photochemical properties have not yet been fully determined. We monitored MB binding, aggregation and its ability to release singlet oxygen (1O2) on irradiation when interacting with mitochondrial suspensions. MB actively binds to mitochondria and enters the matrix in a manner stimulated by the mitochondrial proton potential and by the increase in mitochondrial concentrations. The greater accumulation of MB in mitochondria with elevated proton potentials or those treated with high concentrations of MB results in the formation of MB dimers, previously shown to be less effective generators of 1O2. Accumulation of MB within mitochondria with high membrane potentials also results in the reduction of MB to the photochemically inactive leuco-MB. Indeed, irradiation of mitochondria with high proton potentials in the presence of MB results in the generation of approximately half the quantity of 1O2 compared with 1O2 generated in mitochondria with low proton potentials. These differences in photochemical properties should influence the cytotoxic effects of photodynamic treatment in the presence of MB.

Metalloproteinase inhibitors improve the recovery and hemostatic function of in vitro-aged or -injured mouse platelets

Platelet transfusions are a crucial component of support for patients with severe thrombocytopenia. Storage of platelet concentrates, however, is associated with a reduction in platelet posttransfusion recovery and hemostatic function. In this study, we established a model of mitochondrial injury that resembles platelet storage lesion. Mitochondrial injury, provoked by incubation of platelets with carbonyl cyanide m-chlorophenylhydrazone (CCCP), led to reduced posttransfusion recovery in mice, an effect that directly correlated with the duration of treatment. Damaged platelets were characterized by shape change, disruption of membrane asymmetry, surface expression of P-selectin, and profound proteolysis of GPIbalpha. Using our model, we identified a key role for endogenous metalloproteinase(s) in platelet clearance, as their inhibition markedly improved posttransfusion recovery of both the mitochondria-injured and in vitro-aged mouse platelets. Metalloproteinase inhibition also prevented proteolysis of GPIbalpha on damaged platelets, thereby improving the hemostatic function of these cells in vivo. We propose that inhibition of metalloproteinase activity during storage could significantly improve the effectiveness of platelet transfusions. Surface expression of GPIbalpha might be a powerful marker to determine the quality of platelet concentrates, because it reflects metalloproteinase activity in vitro.

Staining of cellular mitochondria with LDS-751

We have found the dye LDS-751 to bind almost exclusively to mitochondria when incubated with viable, nucleated cells. Treatment of cells with the nuclear stain acridine orange and LDS-751 revealed little colocalization when the cells were examined by confocal microscopy. Staining with the dye rhodamine 123, which is known to bind polarized mitochondria, was virtually identical to the pattern observed with LDS-751. This staining pattern was observed to be consistent over a range of 0.02-20 microg/ml LDS-751 and was consistent between both fibroblasts and monocytes. Depolarization of mitochondria with the mitochondrial depolarizing agents phenyl arsine oxide and carbonyl cyanide m-chlorophenylhydrazone (CCCP) dramatically reduced both LDS-751 staining, and rhodamine 123 fluorescence. Taken together, these results suggest that LDS-751 is excluded from the nucleus and binds the polarized membranes of mitochondria. Given this, interpretation of LDS-751 fluorescence as being indicative of nuclear status, as is commonly done to discriminate between leukocytes and erythrocytes, is unwarranted and may lead to erroneous conclusions if mitochondria become depolarized upon processing.

Glucose induces a Na(+),K(+)-ATPase-dependent transient hyperpolarization in human sperm. I. Induction of changes in plasma membrane potential by the proton ionophore CCCP

When human sperm was incubated in medium deprived of glucose, glucose restoration caused a transient hyperpolarization of the plasma membrane. This hyperpolarization was also induced by fructose but not by 2-deoxyglucose, a substrate that cannot be metabolized. The hyperpolarization was inhibited by NaF, a glycolysis inhibitor, but not by mitochondrial inhibitors (cyanide, rotenone and antimycin), suggesting that it depended on glycolysis. Furthermore, the hyperpolarization was still induced in medium containing a high concentration of KCl and was insensitive to the K(+) channel blocker TEA and the Cl(-) channel blocker niflumic acid, but it was blocked by ouabain. This suggested that upon glucose addition, there was an increase in the concentration of ATP, that in turns increased the Na(+),K(+)-ATPase activity. Since this pump is electrogenic (2K(+)/3Na(+)) the plasma membrane hyperpolarized. On the other hand, CCCP, a proton ionophore, inhibited the hyperpolarization induced by glucose. When CCCP was added to glucose-treated hyperpolarized sperm, it caused a depolarization that triggered a Ca(2+) influx sensitive to nickel, an inhibitor of voltage-dependent calcium channels. Moreover, CCCP caused hyperpolarization in sperm incubated in medium without calcium, a known condition that depolarizes sperm. This indicated that CCCP induced proton permeability in the plasma membrane that was able to change the membrane potential to a value corresponding to the E(H) and that was also able to clamp it, so that it prevented the hyperpolarization induced by glucose.

Growth of the yeast Saccharomyces cerevisiae on a non-fermentable substrate: control of energetic yield by the amount of mitochondria

The purpose of this study was to investigate the long-term control of ATP synthesis during the course of Saccharomyces cerevisiae batch grown on lactate, a purely respiratory substrate. For this, we used a respirometric and on-line calorimetric approach to analyse the energetic balances and the control of energetic metabolism during growth. Enthalpic growth yields assessed by enthalpy balance (taking account of substrate consumption, by-product accumulation, biomass formation and heat dissipation) remained constant during the entire exponential growth. Moreover, at the same time, a parallel decrease in basal respiratory rate and enthalpy flux occurred. It is shown that the decrease in respiration corresponds to a decrease in the amount of mitochondria per cell but not to a change of steady state of oxidative phosphorylation. Taking into account the part of energy used for maintenance, it can be concluded that mitochondria by themselves are the major heat dissipative system in a fully aerobic metabolism, and that the decrease in the amount of mitochondria when growth rate decreases leads to an enthalpic growth yield constant.

The use of chloromethyl-X-rosamine (Mitotracker red) to measure loss of mitochondrial membrane potential in apoptotic cells is incompatible with cell fixation

BACKGROUND

A recent report by Macho et al. (Cytometry 25: 333-340, 1996) described the use of chloromethyl-X-rosamine (CMX-Ros) as a fixable probe for detection of loss of mitochondrial membrane potential (psi(mit)), an early event in many models of apoptosis. However, this previous report lacked a description of any direct comparisons between pre- and post-fixation analyses of normal and apoptotic cells stained with CMX-Ros.

METHODS

Using a variety of cell types, we investigated the effect of paraformaldehyde fixation on cellular retention of CMX-Ros and the implications of this for the subsequent analysis of changes in psi(mit) in cells undergoing apoptosis.

RESULTS

We found that following fixation, the resolution between normal cells with polarized mitochondria and apoptotic cells with depolarized mitochondria is reduced to the extent that accurate discrimination between the cell types is no longer possible.

CONCLUSIONS

Overall, our results are consistent with CMX-Ros being a valid probe for psi(mit) in intact cells but only when the cells are stained and analyzed immediately. Thus, our results suggest that the proposed applications for CMX-Ros in multiple parameter analysis of fixed cells are inappropriate and will lead to spurious results.

Clearance of large Ca2+ loads in a single smooth muscle cell: examination of the role of mitochondrial Ca2+ uptake and intracellular pH

Redistribution of cytosolic free Ca2+ following Ca2+ influx into the cytoplasm was studied in single smooth muscle cells isolated from guinea-pig urinary bladder. Voltage-clamped cells were loaded with a low-affinity fluorophore Indo-1FF. A decay of free intracellular Ca2+ ([Ca2+]i) after the termination of the depolarizing pulse (1 s from -50 mV to +20 mV) was fitted with a single exponential and the effect of various substances on the time constant was compared. At a holding potential of +80 mV the [Ca2+]i decay was 1.56 times slower compared to that at -50 mV suggesting the presence of a voltage-dependent process redistributing Ca2+. In the presence of cyclopiazonic acid (CPA, 10 microM), an inhibitor of sarco(endo)plasmatic Ca2+ pump (SERCa), the [Ca2+]i decay was 3.93 times slower than that in the absence of the inhibitor. Introduction of a polycation Ruthenium Red (RR) (20 microM), an inhibitor of the mitochondrial Ca2+ uniporter, into a cell or collapsing a transmitochondrial H+ gradient with the protonophore CCCP (2 microM) slowed down the [Ca2+]i decay 6.05-fold and 9.78-fold, respectively. The apparent amplitude of [Ca2+]i increments was also increased by CCCP. Increasing H+ buffering power in the intracellular solution from 10 mM to 40 mM of HEPES greatly reduced the effect of CCCP on [Ca2+]i decay. A further increase in HEPES concentration to 100 mM eliminated the effects of CCCP both on the time course of [Ca2+]i decay and on the amplitude of [Ca2+]i increment. Perfusion of RR together with 100 mM HEPES into the cytoplasm was without effect on the decay time course of [Ca2+]i. The effect of CPA on [Ca2+]i decay was also reduced in cells loaded with 100 mM HEPES; the time constant in the presence of CPA was slowed down by a factor of 2.18. Application of 10 mM Na(+)-butyrate to the cells loaded with 10 mM HEPES resulted in a slowing down of [Ca2+]i decay: the time constant was increased by a factor of 5.84. Measurement of intracellular pH with SNARF-1 confirmed cytoplasmic acidification during application of Na(+)-butyrate and CCCP. It is concluded that the contribution of mitochondrial Ca2+ uptake to the rapid [Ca2+]i decay is much less than could be extrapolated from action of protonophores in these smooth muscle cells. The results also demonstrate the importance of intracellular pH for Ca2+ handling in the cytoplasm of smooth muscle cells.

Identification of a sequence motif that confers SecB dependence on a SecB-independent secretory protein in vivo

SecB is a cytosolic chaperone which facilitates the transport of a subset of proteins, including membrane proteins such as PhoE and LamB and some periplasmic proteins such as maltose-binding protein, in Escherichia coli. However, not all proteins require SecB for transport, and proteins such as ribose-binding protein are exported efficiently even in SecB-null strains. The characteristics which confer SecB dependence on some proteins but not others have not been defined. To determine the sequence characteristics that are responsible for the SecB requirement, we have inserted a systematic series of short, polymeric sequences into the SecB-independent protein alkaline phosphatase (PhoA). The extent to which these simple sequences convert alkaline phosphatase into a SecB-requiring protein was evaluated in vivo. Using this approach we have examined the roles of the polarity and charge of the sequence, as well as its location within the mature region, in conferring SecB dependence. We find that an insert with as few as 10 residues, of which 3 are basic, confers SecB dependence and that the mutant protein is efficiently exported in the presence of SecB. Remarkably, the basic motifs caused the protein to be translocated in a strict membrane potential-dependent fashion, indicating that the membrane potential is not a barrier to, but rather a requirement for, translocation of the motif. The alkaline phosphatase mutants most sensitive to the loss of SecB are those most sensitive to inhibition of SecA via azide treatment, consistent with the necessity for formation of a preprotein-SecB-SecA complex. Furthermore, the impact of the basic motif depends on location within the mature protein and parallels the accessibility of the location to the secretion apparatus.

Dissociation of colonic apical Na/H exchange activity from bulk cytoplasmic pH

Intracellular acidification by stimuli rather than CO2 fails to stimulate colonic apical Na/H ex-change and Na absorption. We examined whether Na absorption could be stimulated in the absence of changes in cytoplasmic pH (pHi). Distal colon of male Sprague-Dawley rats was used for pHi measurements with 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein and for flux measurements in Ussing chambers. In 21 mM HCO3-Ringer, increasing PCO2 from 20 to 70 mmHg decreased pHi from 7.51 to 7.03 and increased net Na flux (JnetNa) from 4.2 +/- 0.4 to 6.8 +/- 0.6 mu eq.cm-2.h-1. Similar increases in JnetNa occurred in the absence of mucosal CI and in the presence of phalloidin to inhibit microfilaments or penzolamide to inhibit membrane-bound carbonic anhydrase. sohydric increases in Pco2 did not alter pHi but stimulated JnetNa from 5.1 +/- 0.6 to 7.2 +/- 0.8 mu eq.cm-2.h-1. Carbonyl cyanide m-chlorophenylhydrazone (CCCP) decreased pHi from 7.45 to 7.35 but did not stimulate JnetNa. Butyrate (25 mM) decreased pHi from 7.15 to 7.02 with recovery to baseline within 6 min; however, JnetNa increased by 2.2 mu eq.cm-2.h-1 for 60 min. We conclude that apical Na/H exchange activity is unresponsive to changes in bulk pHi and is independent of Cl/HCO3 exchange, microfilaments, and membrane-bound carbonic anhydrase. The presence of an H-tight, CO2, and butyrate-permeable subapical domain is postulated.

Effect of the spin-trapping compound N-tert-butyl-alpha-phenylnitrone on protein oxidation and life span

N-tert-Butyl-alpha-phenylnitrone (PBN), a lipophilic spin-trapping compound, has been reported to decrease the concentration of protein carbonyls, the products of protein oxidation, in the brain of old gerbils to virtually the level found in the young gerbils (Carney, J. M., et al. (1991) Proc. Natl. Acad. Sci. USA 88, 3633-3636). The validity of this finding as well as that of the commonly used 2,4-dinitrophenylhydrazine procedure for the measurement of protein carbonyls was recently called into question by Cao and Cutler ((1995) Arch. Biochem. Biophys. 320, 106-114). The objective of the present study was to examine some of the relevant issues such as (a) whether the original findings on the effects of PBN can be confirmed, (b) whether similar effects of PBN occur in other species and tissues, and (c) whether PBN affects the life span of animals. Results of this study provide confirmation of the original finding that PBN indeed causes a decrease in protein carbonyl content in the gerbil brain cortex. However, a similar effect is not observed in the gerbil heart or the mouse brain cortex. Effects of PBN on protein carbonyls are thus variable depending upon tissue and species. PBN administration did not extend the life span of houseflies and at relatively high concentrations it was found to be toxic.

The effect of pH on the growth and motility of Rhodobacter sphaeroides WS8 and the nature of the driving force of the flagellar motor

Rhodobacter sphaeroides WS8 grew, and swam vigorously, over the pH range 6 to 9. Sustained motility was, however, observed in populations of cells resuspended at pH values between 4.9 and 10.4, although the mean run speed was reduced at the extremes of pH. The ability of R. sphaeroides to swim in strong alkaline conditions prompted the question of whether motility at alkaline pH was powered by a sodium motive force, as has been found in the facultative alkalophilic Bacillus and Vibrio species, particularly as motility was found to be sensitive to the sodium channel inhibitor amiloride. The nature of the driving force of the flagellar motor was therefore investigated. It was found that R. sphaeroides was motile over the same pH range in the absence and presence of sodium ions. The protonophore CCCP was found to inhibit motility under all conditions, whereas monensin, an inhibitor of sodium pumps, had no effect upon motility in the presence or absence of sodium. It was concluded that the delta p is the driving force for the flagellar motor in R. sphaeroides at all values of pH. Amiloride, a specific inhibitor of the sodium-driven flagellar motor in alkalophilic Bacillus and Vibrio was shown to act non-specifically on the proton driven motor of R. sphaeroides, reducing the swimming speed of this organism in media with and without sodium to the same extent and over the complete pH range. Measurement of the delta p by using the electrochromic absorbance change of the carotenoid pigments to measure delta psi and 31P-NMR to measure delta pH showed that the maximum delta p was about -215 mV. At pH 10 the cells swam more slowly and the delta p was about -90 mV. These data suggest that the flagellar motor of R. sphaeroides is proton-driven under all conditions with a threshold for motor rotation below -90 mV and saturation at above -90 mV and below -215 mV.

Confocal laser scanning microscopy of mitochondria within microspore tetrads of plants using rhodamine 123 as a fluorescent vital stain

The present study demonstrates that rhodamine 123 penetrates the callose walls surrounding plant microspores before they are released from tetrads. The stain accumulates in active mitochondria due to the electrical potential across the mitochondrial membrane. Accumulation of dye does not occur in mitochondria of fixed cells and fades quickly when mitochondrial activity is inhibited by exposure to carbonyl cyanide m-chlorophenyl hydrazone. Rhodamine can be used as a viability test for microspores still within tetrads, thus making it possible to determine when during development genes leading to pollen sterility are expressed. Rhodamine 123 is excited by blue (550 nm) light and can thus be used with confocal laser scanning microscopy. Anthers of Nicotiana tabacum, Oenothera villaricae, Silene dioica and Lycopersicum esculentum were studied here.

Effects of modulations of the energetic metabolism on the mortality of cultured cells

Since cells are open systems which exchange material with their surroundings, they can be considered as open systems far from equilibrium and in this way, they follow the principles of thermodynamics of open systems. This approach stresses the fact that cells optimize their use of energy according to their functions. However, with time and/or under environmental challenges, cells can reorganize themselves at other lower levels of energy production and utilization (Toussaint et al. (1991) Mech. Ageing Dev. 61, 45-64). Considered as optimized systems, cells can adapt their behaviours according to the balance between, on one side, their energetic potential and the level of their defence systems, and on the other side, the intensity of the stress. Mainly three types of behaviour can be theoretically predicted. If the stresses are very low, the damages generated are instantaneously repaired and the cellular system remains at its steady state of energy production and utilization. If the stresses are of an intermediary intensity, it is predicted that the cell can leave its steady state of energy production and utilization and find a new one characterized by a lower level of entropy production and a higher level of errors. Third, if the stresses are of a very high intensity which can be cytotoxic, the level of the energetic potential of the cell is directly related to cell survival. We tested the latter prediction in the present work in two ways. First, the level of energy production was lowered by partially uncoupling the mitochondria. Then the effect of stresses under tert-butylhydroperoxide or ethanol was investigated in order to look for a synergistic effect on cell death with the mitochondria uncoupling. Secondly, the effect of a modification of the energetic sources during the stress was tested. Besides a protective effect found with specific defence systems, the presence of energetic metabolites such as D-glucose, pyruvate/malate, glutamate/malate, was tested and found to be protective. The effect of a stimulator of the energetic metabolism, naftidrofuryl oxalate, was also investigated and found protective. The experimental data provide good evidence that energetic factors can modulate the resistance of cells to various stresses.

The ATP-driven Na(+)-pump in the plasma membrane of the marine unicellular alga, Platymonas viridis

The ATP-supported 22NA+ uptake by plasma membrane vesicles from the marine microalga, Platymonas viridis, was studied. At pH 7 in the medium, Na+ uptake did not occur in the presence of ATP although delta pH across the plasma membrane was generated. The ATP-dependent Na+ uptake was induced by adding the protonophore, ClCCP. At pH 8, Na+ uptake took place when ATP was added even without ClCCP. The delta pH generated across the plasma membrane was negligible under these conditions. The Na+ uptake at pH 8 was not affected by ClCCP and amiloride, an inhibitor of the Na+/H+ antiporter. It is concluded that the ATP-supported Na+ uptake by Pl. viridis vesicles is catalyzed by Na(+)-ATPase.

Role of the protonmotive force and of the state of the lipids in the in vivo protein secretion in Corynebacterium glutamicum, a gram-positive bacterium

PS1 is a protein translocated across the cytoplasmic membrane of Corynebacterium glutamicum, a Gram-positive bacterium. Western blots of whole cell extracts showed the presence of two bands associated with the mature and the precursor forms. Addition of chloramphenicol led to the disappearance of the precursor form while dissipation of the protonmotive force (delta microH) prior to the addition of chloramphenicol prevented the maturation of the precursor. Dissipation of delta microH prior to a pulse chase experiment resulted in a complete block on translocation; regeneration of delta microH allowed the translocation of PS1 synthesized in its absence. On the other hand, dissipation of delta microH immediately after a pulse period had little effect on PS1 secretion. Lowering the temperature to 10 degrees C at the end of the pulse period completely inhibited secretion. The efficiency of secretion as a function of increasing temperature followed closely the order-to-disorder transition of the membrane lipids as detected by fluorescence anisotropy of diphenylhexatriene. Taken together, the results show that delta microH and the state of the lipids affect different steps of PS1 secretion.

Quick and accurate method to convert BCECF fluorescence to pHi: calibration in three different types of cell preparations

A rapid, easy, and accurate method for converting the fluorescence of BCECF to pH, as an alternative to the nigericin method, is described. The ratio of the fluorescence intensities for BCECF can be converted to pH between 4 and 9 by a formula similar to the one used to calculate [Ca2+]i from the fluorescence of fura2. The formula is inverted because H+ binding to BCECF causes a decrease in fluorescence, whereas Ca2+ binding to fura2 causes an increase in fluorescence. The ratio of the fluorescence intensities is a sigmoidal function of the [H+] between pH 4 and 9 with an essentially linear mid region from pH 6 to 8. This calibration procedure in cells is similar to the popular method for fura2 where ionomycin, Ca2+, and an alkaline EGTA solution are added in succession to change the intracellular pCa from 4 to 9. For BCECF in cells, a protonophore, FCCP or CCCP, is added and the cells are titrated with acid to an intracellular pH of 4 and then back to pH 9 with base by observing the gradual change in fluorescence as it asymptotically reaches its limiting minimum and maximum values. This method does not require changing the medium to one with high KCl to depolarize the membrane potential nor does the proton concentration need to be equilibrated across the plasma membrane. The technique can be used to calibrate BCECF in sheets of cells, as well as suspensions of cells over a wide range of pH sensitivities.

Effect of phloretin on the carrier-mediated electrically silent ion fluxes through the bilayer lipid membrane: measurements of pH shifts near the membrane by pH microelectrode

The effect of phloretin on the carrier-mediated electrically silent ion fluxes through the bilayer lipid membrane (BLM) was studied. The measurements were carried out according to our conventional technique, i.e. electrical potential recording in the presence of a protonophore, and by a new method--direct measurements of pH shifts in the unstirred layers of the BLM by pH microelectrode. Both techniques gave similar results. It was shown that the addition of phloretin increased the rate of cation/H+ exchange induced by nigericin and decreased the rate of anion/OH(-)-exchange induced by tributyltin. The effect of phloretin was higher in the presence of cholesterol in the BLM. Cholesterol decreased the nigericin- and tributyltin-induced fluxes under our experimental conditions. The application of an external voltage to the membrane had no effect on the ion fluxes thereby showing that these fluxes were electroneutral. The most probable explanation of these results bases on the effect of the membrane dipole potential on the electroneutral fluxes of ions. The possible mechanism of the dipole potential effect on the carrier-mediated electrically silent ion fluxes was discussed in terms of two competing hypotheses--the translocation through the membrane or the reactions at the membrane surface being the rate-limiting steps of the whole transport process.

A novel mechanism of cation/substrate cotransport: Na+/H+/adenosine cotransport in Vibrio parahaemolyticus

Adenosine is actively transported with Na+ in Vibrio parahaemolyticus (Sakai, Y., Tsuda, M., Tsuchiya, T. (1987) Biochim, Biophys. Acta 893, 43-48). The proton conductor carbonylcyanide m-chlorophenylhydrazone, CCCP, strongly inhibited active transport of adenosine at pH 8.5 as well as at pH 7.0. This seemed peculiar because the driving force, an electrochemical potential of Na+, is established by the Na(+)-extruding respiratory chain at pH 8.5 in this organism, although it is established by the function of the Na+/H+ antiporter at pH 7.0. This suggested that H+ might be involved in the adenosine transport. We detected H+ uptake induced by adenosine influx in V. parahaemolyticus cells in the presence of Na+, but not in its absence, suggesting the occurrence of Na+/H+/adenosine cotransport. We isolated formycin A-resistant mutants which showed defective adenosine transport. The mutation resulted in simultaneous losses of Na+ uptake and H+ uptake induced by adenosine. In revertants from these mutants the Na+ uptake and H+ uptake were restored simultaneously. The frequencies of reversion were in the order of 10(-7), indicating that the mutations were single mutations; namely that Na+/adenosine cotransport and H+/adenosine cotransport took place via the same carrier. Thus, we conclude that adenosine is transported by the novel mechanism of Na+/H+/adenosine cotransport in V. parahaemolyticus.

Voltage-dependent conductance for alamethicin in phospholipid vesicles. A test for the mechanism of gating

The ion currents induced by alamethicin were investigated in unilamellar vesicles using electron paramagnetic resonance probe techniques. The peptide induced currents were examined as a function of the membrane bound peptide concentration, and as a function of the transmembrane electrical potential. Because of the favorable partitioning of alamethicin to membranes and the large membrane area to aqueous volume in vesicle suspensions, these measurements could be carried out under conditions where all the alamethicin was membrane bound. Over the concentration range examined, the peptide induced conductances increased approximately with the fourth power of the membrane bound peptide concentration, indicating a channel molecularity of four. When the alamethicin induced currents were examined as a function of voltage, they exhibited a superlinear behavior similar to that seen in planar bilayers. Evidence for the voltage-dependent conduction of alamethicin was also observed in the time dependence of vesicle depolarization. These observations indicate that the voltage-dependent behavior of alamethicin can occur in the absence of a voltage-dependent phase partitioning. That is, a voltage-dependent conformational rearrangement for membrane bound alamethicin leads to a voltage-dependent activity.

Ca(2+)-dependent and independent mitochondrial damage in hepatocellular injury

The alterations of mitochondrial membrane potential during the development of irreversible cell damage were investigated by measuring rhodamine-123 uptake and distribution in primary cultures as well as in suspensions of rat hepatocytes exposed to different toxic agents. Direct and indirect mechanisms of mitochondrial damage have been identified and a role for Ca2+ in the development of this type of injury by selected compounds was assessed by using extracellular as well as intracellular Ca2+ chelators. In addition, mitochondrial uncoupling by carbonylcyanide-m-chloro-phenylhydrazone (CCCP) resulted in a marked depletion of cellular ATP that was followed by an increase in cytosolic Ca2+ concentration, immediately preceding cell death. These results support the existence of a close relationship linking, in a sort of reverberating circuit, the occurrence of mitochondrial dysfunction and the alterations in cellular Ca2+ homeostasis during hepatocyte injury.

Proton flux in large unilamellar vesicles in response to membrane potentials and pH gradients

The transport of protons across liposomes composed of phosphatidylcholine in response to electrical potentials or pH gradients has been investigated. The results support three major conclusions. The first of these concerns the need for reliable measurements of electrical potentials and pH gradients. It is shown that the potential probe tetraphenylphosphonium and the pH probe methylamine provide accurate and self consistent measures of electrical potentials and pH gradients respectively in these systems. Second, it is shown by two independent techniques that the pH gradients induced in response to valinomycin and potassium dependent electrical potentials are significantly smaller than would be expected for electrochemical equilibrium. The pH gradients observed are stable over an 8 h time course and are sensitive to the ionic composition of the buffers employed, where the presence of external sodium results in the smallest induced pH gradients. These results are discussed in terms of current models of proton conductance across membranes. In a final area of investigation, it is shown that valinomycin and carbonyl cyanide m-chlorophenyl hydrazone (CCCP) can transport sodium ions in a synergistic manner.

A respiratory-driven and an artificially driven ATP synthesis in mutants of Vibrio parahaemolyticus lacking H+-translocating ATPase

Mutants of Vibrio parahaemolyticus lacking the H+-translocating ATPase were isolated to evaluate both the role of this enzyme and the possibility of the involvement of other cation-translocating ATPase in the energy transduction in this organism. Dicyclohexylcarbodiimide-sensitive ATPase activity which represents the H+-translocating ATPase was not detected either in the membrane vesicles or in the cytosol of the mutants. Three major subunits, alpha, beta and gamma, of the H+-translocating ATPase were missing in the membranes of the mutants. Although ATP was synthesized in wild type cells when an artificial H+ gradient was imposed, little ATP was synthesized in the mutants. However, we observed a large ATP synthesis driven by the respiration not only in the wild type but also in the mutants. The respiratory-driven ATP synthesis in wild type was inhibited by an H+ conductor, carbonylcyanide m-chlorophenylhydrazone, by about 50%. On the other hand, the ATP synthesis in the mutants was not affected by the H+ conductor. Since this organism possesses a respiratory Na+ pump, Na+-coupled ATP synthesis might take place. In fact, we observed some ATP synthesis driven by an artificially imposed Na+ gradient both in the wild type and the mutant.

Isolation, molecular characterization and expression of the ushB gene of Salmonella typhimurium which encodes a membrane-bound UDP-sugar hydrolase

The UDP-sugar hydrolase of Salmonella typhimurium has previously been reported to be located in both the inner and the outer membrane. We have cloned the gene, designated ushB, encoding this enzyme and determined its nucleotide sequence. No significant sequence homology with the periplasmic UDP-sugar hydrolase of Escherichia coli was found at either the DNA or protein level. However, a sequence is detectable, in the E. coli genome, which weakly hybridizes with a specific ushB probe. Polypeptide analysis has allowed the identification of the Salmonella hydrolase which has an Mr of 28,349 as compared to an Mr of 60,767 for the E. coli hydrolase. Most of the protein (approximately 90%) is located in the inner membrane. Two independent membrane fractionation procedures indicate that the remainder may be associated with the outer membrane. The deduced primary structure indicates the presence of an N-terminal signal peptide, although certain features of the region surrounding the putative processing site indicate that processing may be inefficient, or may not occur. Experiments with several inhibitors of signal peptidase function fail to demonstrate the appearance of a precursor form.

Cytochrome b is necessary for the assembly of subunit VII in the cytochrome b-c1 complex of yeast mitochondria

The synthesis and assembly of subunit VII, the Q-binding protein of the cytochrome b-c1 complex, into the inner mitochondrial membrane has been compared in wild-type yeast cells and in a mutant cell line lacking cytochrome b. Both immunoblotting and immunoprecipitation analysis with specific antiserum against subunit VII indicated that this subunit is not detectable in the mutant as compared to the wild-type mitochondria. However, labeling in vivo of the cytochrome b deficient yeast cells in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone clearly demonstrated that subunit VII was synthesized in the mutant cells to the same extent as in the wild-type cells. Incubation of subunit VII, synthesized in vitro in a reticulocyte lysate programmed with yeast RNA, with mitochondria isolated from both wild-type and cytochrome b deficient yeast cells revealed that the subunit VII was transported into the wild-type mitochondria into a compartment where it was resistant to digestion by exogenous proteinase K. By contrast, subunit VII was bound in lowered amounts to the cytochrome b deficient mitochondria where it remained sensitive to digestion by exogenous proteinase K, suggesting that the import of subunit VII may be impaired due to the lack of cytochrome b. Furthermore, subunit VII was synthesized both in vivo and in vitro with the same molecular mass as the mature form of this protein.

Temperature jump as a new technique to study the kinetics of fast transport of protons across membranes

Application of a temperature jump (2.5 degrees C) to a suspension of liposomes, having phosphate (delta pK/delta T approximately 0.005) as the internal buffer and tris(hydroxymethyl)aminomethane (delta pK/delta T approximately 0.031) as the external buffer, created a delta pH (pHin - pHout) of positive sign in ca. 5 microseconds. Decay of this delta pH was monitored by using the fluorescent pH indicator 8-hydroxy-1,3,6-pyrenetrisulfonic acid entrapped inside the liposome. This technique is useful to study transmembrane proton movement in the time range 5 microseconds-10 s at physiological pH values. The kinetics of proton transport aided by ion carriers such as nigericin, monensin, carbonyl cyanide m-chlorophenylhydrazone (CCCP), and valinomycin were studied by our method. The electrogenic nature of transport by CCCP and valinomycin and electroneutral ion transport by nigericin and monensin were shown. From the kinetics of proton transport aided by gramicidin, the time-averaged single-channel conductance of gramicidin channels was estimated to be (2.1 +/- 0.5) X 10(-16) S for H+ at pH 7.5.

Electrical stability of artificial membranes

The electrical breakdown potential of the planar lipid membranes has been shown to decrease following UV-induced lipid peroxidation, action of phospholipase A2, adsorption of protamine sulphate and expansion of the membrane by hydrostatic pressure. Membrane potential generated upon the addition of potassium acetate (or ammonium sulphate) and protonophore CCCP to liposomes, when large enough, was also able to break membranes; this was suggested by liposome swelling and a rapid decrease in suspension turbidity. UV-irradiation decreased liposomal membrane breakdown potential, while cholesterol increased it. Detergents and water-soluble products of lipid peroxidation decreased the breakdown potential. The possible role of the membrane electrical breakdown phenomenon in cell pathology is discussed.

Uptake of adriamycin into large unilamellar vesicles in response to a pH gradient

Previous work has shown that adriamycin can be accumulated into large unilamellar vesicle (LUV) systems in response to K+ diffusion potential established by valinomycin. It is demonstrated here that adriamycin can also be rapidly and efficiently accumulated into egg phosphatidylcholine (egg PC) and egg PC-cholesterol (1:1) LUVs in response to a transmembrane pH gradient (interior acidic) in the absence of ionophores. This 'active' loading gives rise to trapping efficiencies as high as 98%, interior drug concentrations as high as 100 mM and significantly enhances drug retention within the vesicles. This procedure may be of general utility for loading liposomal systems for in vivo drug delivery.

An electrical and structural characterization of H+/OH- currents in phospholipid vesicles

Paramagnetic amphiphiles have been utilized to measure and characterize electrogenic H+/OH- ion transport in a series of model membrane systems. Membrane conductivity to H+/OH- ions varies with the method of vesicle preparation and with the level of saturation of the membrane phospholipid. Small sonicated vesicles have the lowest conductivities by approximately an order of magnitude compared to reverse-phase or ether-injection vesicle systems. This conductivity is particularly sensitive to the presence of polyunsaturated lipids in the vesicle membrane. The current-delta pH dependence of the H+/OH- conductivity shows a nonideal behavior and renders the phenomenological membrane permeability dependent upon the experimental value of delta pH that is chosen. These factors can account for much, if not all, of the variability in the published values for the H+/OH- permeability of model membranes. A procedure has been developed to establish and estimate changes in the dipole potential of vesicle bilayers. Using this method, we demonstrate that H+/OH- currents are insensitive to alterations in the membrane dipole field, a result that suggests that these currents are not rate limited by diffusion over simple electrostatic barriers in the membrane interior. In addition, conduction in D2O has been examined, and we find that there is little difference in the magnitudes of D+/OD- currents compared to H+/OH- currents in vesicle systems.

Transient currents carried by the uncoupler, carbonyl cyanide m-chlorophenylhydrazone

The weak acid uncoupler, carbonyl cyanide m-chlorophenylhydrazone, carries protons across lipid membranes. As predicted by the carrier model, at low pH, the current changes immediately following a jump in applied potential and then remains constant. By contrast at high pH, the currents relax from an initial value to a lower value as the carrier anions redistribute in the membrane. These relaxations are slower than those seen with other lipid-soluble anions which presumably explains why they had not been detected previously.

Calcium-induced oscillations in K+ conductance and membrane potential of human erythrocytes mediated by the ionophore A23187

The time-dependence of ionophore A23187-induced changes in the conductance of the Ca2+-sensitive K+ channels of the human red cell has been monitored with ion-specific electrodes. The membrane potential was reflected in CCCP-mediated pH changes in a buffer-free extracellular medium, and changes in extracellular K+ activity and electrode potential of an extracellular Ca2+-electrode were recorded. Within a narrow range of ionophore-mediated Ca2+ influx, the above-mentioned parameters were found to oscillate when ionophore was added to a suspension of glucose-fed cells. The period of oscillation was about 2 min/cycle depending on ionophore concentration, and the amplitude of hyperpolarization was about 60 mV, corresponding to a maximal gK+ of the same magnitude as gCl-. Without CCCP present no oscillation in K+ conductance was observed. The Ca2+ affinity for the opening process was in the micromolar range. The closing of the K+ channels was a spontaneous process in that the depolarization was well under way before the Ca2+-ATPase-mediated Ca2+ net efflux started. Below the Ca2+ influx range for oscillations, no response was observed for up to 20 min after the addition of ionophore. Above the upper limit, a permanent hyperpolarization resulted with an extracellular K+ activity increasing monotonically as a function of time. In experiments with ATP-depleted cells, responses of the latter type ensued at all ionophore concentrations above the lower limit. Addition of surplus EGTA to suspensions of hyperpolarized cells restores the normal membrane potential in the case of glucose-fed cells, whereas the K+-channels in ATP-depleted cells remained open.

Proton permeability of liposomes from natural phospholipid mixtures

A method to determine the proton permeability coefficient of phospholipid membrane with the fluorescent probe pyranine is described. Very high proton permeability coefficients of liposomes from natural extracts are measured with great accuracy. The proton permeability appears to be linearly related to the fluidity of the bilayers. This relation as well as the comparison of the activation energies of proton permeability and fluidity support the hypothesis (Nichols J.W. and Deamer D.W. (1980) Proc. Natl. Acad. Sci. USA 77, 2038--2042) of a transfer process along a network of hydrogen bonded water molecules. It is suggested that the common lipid characteristics of biological membranes (net surface charge and unsaturation) favor a high proton permeability.