[Refinement of the French sociotropy-autonomy scale: Validation of a 20-item measure of social dependency among first-year students at the university]. / Révision de l'échelle française de mesure de la sociotropie et de l'autonomie : validation d'une échelle à 20 items mesurant de dépendance sociale de primo-entrants à l'université.

OBJECTIVE: Sociotropy and autonomy have been described as personality styles promoting the occurrence of stress in individuals. The SAS (for sociotropy-autonomy scale) corresponds to a 60-item instrument devoted to sociotropy and autonomy estimation in various populations. However, the different SAS versions display variations in item scoring, in scale structure and in factor composition. Furthermore, there is a lack of scale invariance analysis. Consistent with a larger work dedicated to understanding contributors of students' achievement during their trainings, the objective of this study was devoted to a refinement of French SAS item properties and to a measure of scale invariance in order to ensure that the French SAS be a trustable tool to measure sociotropy and autonomy among first- year students. Because a preliminary analysis invalidated several SAS items, a second objective has consisted of the definition and validation of a new scale estimating social dependency in students. METHODS: In all, 2365 students registered in first year of technological training (n=778) and health training (n=1587) were enrolled. They were asked to electronically answer the 60-item French SAS. The responses were collected between October and November 2017 for students registered in technological formation, and between March and April 2018 for health students. Item-score correlation coefficients (ritem-score) and anti-image correlation coefficients (AIC) were calculated for each item, and threshold values (ritem-score>0.3 ; AIC>0.6) were considered as acceptance criteria. Factor analyses were run in order to determine scale structure. Internal consistency was deduced from Cronbach's α, McDonald ω and Great Lower Bound (GLB) coefficients. Convergent and discriminant validities were analysed in considering construct reliability coefficient (CR>0.7), average variance extracted (AVE>0.4), mean shared variance and squared correlation coefficient calculated between two factors, as validity criteria. Configurational, metric and scalar levels of invariance were analysed prior to statistical comparisons of the scores obtained by different subgroups. RESULTS: In all, 1223 responses were collected and analysed. GLB and ω coefficients calculated for the full SAS indicated unacceptable internal consistency. Of the 60 items, 40 did not meet the acceptance criteria (i. e. ritem-score<0.3 and AIC<0.6). The remaining items had acceptable psychometric properties, and their composition defined a new scale reflecting the measure of social dependency. The overall scale internal consistency was good (ω=0.83, GLB=0.88). Factor analyses resulted in a replicable 5-factor structure including: need of affection (α=0.74, ω=0.74, GLB=0.77), fear of dropping out (α=0.67, ω=0.68, GLB=0.70), fear of loneliness (α=0.61, ω=0.61, GLB=0.67), attention to others (α=0.69, ω=0.69, GLB=0.71) and worry about the disapproval of others (α=0.71, ω=0.71, GLB=0.74). Discriminant validity was satisfied for all factors. Convergent validity was entirely satisfied for need of affection, fear of dropping out and for attention to others, but it was not optimal for fear of loneliness and worry about the disapproval of others. Invariance measurements identified non-invariant items that were discarded from score calculations. Following statistical comparison, it was observed that female students had higher social dependency and fear of dropping out than males. Furthermore, female students registered in health training had stronger attention to others than did their male equivalents. It was also observed that female health students scored better for social dependency, fear of dropping out, attention to others, and importance of others' gaze than their technology-educated counterparts. CONCLUSION: This work has invalidated the use of the overall 60-item French SAS to measure sociotropy and autonomy in first year students. By contrast, the refinement of the French SAS items led to a trustable 20-item instrument to investigate social dependency. Scale invariance characteristics allow confident statistical comparisons between sub-groups. This work shows that first-year female students registered in health or technological trainings exhibit a higher social dependency than males. Furthermore, first-year female health students show more social dependency than their technological counterparts. Because the conditions of recruitment of first-year students in heath formations in France are planned to change in September 2020, future studies will be warranted to analyse their social dependency.

Exploration of mental health of health students: Dental and medical formations promote anhedonia.

OBJECTIVES: Health students usually report to experience stress during their formation. This is due to their exposure to patient's disease or death, to their learning of interpersonal relationships, and to the discovery of health practitioner's responsibility. Anhedonia represents a deficit in experiencing pleasure that is promoted by stressful living conditions. We hypothesized that health formations promote anhedonia. Our objectives have consisted in measuring anhedonia and analyzing its variation and heterogeneity among health students. METHODS: The Temporal Experience of Pleasure Scale (TEPS) was used to assess anhedonia and its anticipatory and consummatory dimensions. TEPS corresponds to an 18-item questionnaire, the score of which is based on a 6-point Likert scale. Low score indicates a high anhedonia propensity. Score differences were analyzed by considering gender, curriculum and formation as independent variables. A cluster analysis was used to explore anhedonia heterogeneity among our sample. RESULTS: We collected 1231 responses. Our data confirm French TEPS as a reliable tool for anhedonia evaluation in dental and medical students. Statistical analyses reveal a significant effect of gender (male>female), curriculum (clinical>preclinical) and formation (dental>medical) on anhedonia propensity. Cluster analysis highlights four sub-groups of students characterized by increasing anhedonia traits and by different gender, formation and curriculum proportions. CONCLUSION: This work describes the first analysis of anhedonia manifestation during dental and medical studies in France. The consequences of our findings for the comprehension of dental and medical students' mental health during their formation are discussed.

Psychometric validation of the French version of the Connor-Davidson Resilience Scale.

OBJECTIVES: Resilience defines the ability to face adversity with positive outcomes. Different scales, including the 25-item Connor-Davidson Resilience Scale (CDRISC), have been elaborated in order to evaluate resilience among various populations. The evaluation of resilience in French populations was impossible until CDRISC was translated into French. In the present work, we aim to validate a French version of CDRISC (f-CDRISC). METHODS: The survey was conducted at Nantes University. Both dental and medical students were eligible. The factor structure of f-CDRISC was determined and its replicability was tested on two sub-samples by exploratory factor analysis (EFA) and parallel analysis (PA). A third student sample was used for confirmatory factorial analysis (CFA). RESULTS: We collected 1210 responses. Four items did not reach acceptance thresholds for reliability and were discarded from the f-CDRISC. EFA and PA of the remaining 21 items highlighted a replicable 3-factor structure that was further confirmed by CFA. Resilience factors included "tolerance to negative affects", "tenacity" and "self-confidence". All factors displayed acceptable to good internal consistency. They were characterized by positive medium to strong correlations with the overall f-CDRISC Scale. Significant positive correlations were also observed between the resilience factors. CONCLUSION: The present work constitutes the first study devoted to a French adaptation of the CDRISC questionnaire. We present evidence showing that the f-CDRISC is a reliable tool for resilience evaluation in French speaking populations.

Can osteopathic manipulative treatment modify the posture in elderly people? - a single-case study.

In this research, we have studied the consequences of three consecutive osteopathic manipulative sessions (OMS) on postural control by using a single-case research (SCR) design. The patient was a 77 years old woman complaining of altered balance and low-back pain. OMS were delivered by a single practitioner. The pain level was self-rated by using a visual Borg scale. The posture was monitored on a force platform. Postural parameters were deduced from the analysis of the centre of foot pressure (CoP) displacement. The statistical significance of the observed differences was established by using an SCR-related effect size indicator (i.e. Taunovlap). Our results indicate that OMS decrease the patient's pain, modify CoP mean position and decreased the length and velocity of the CoP displacement. Furthermore, modifications of the body oscillations were observed after OMS. This work indicates that OMS can improve body balance and that SCR allows the objective evaluation of the consequences of OMS.

Mitochondrial membrane permeabilization produced by PTP, Bax and apoptosis: a 1H-NMR relaxation study.

To analyze the involvement of structured water (bound to macromolecules) in apoptosis-induced mitochondrial outer-membrane permeability, we compared the dynamics of water protons from nuclear magnetic resonance (NMR) data in apoptotic liver mitochondria with that of control mitochondria incubated in vitro with free Ca(2+) (opening of the permeability transition pore, PTP) or with Bax alpha. Our results demonstrate that water molecules in apoptotic mitochondria exhibit an accelerated translational motion of structured water common with that induced by the opening of the PTP, but limited in amplitude. On the other hand, no significant quantitative change in structured water was observed in apoptotic mitochondria, a phenomenon also observed with Bax alpha-induced permeability. We conclude that the changes observed in the different water phases differ both quantitatively and qualitatively during the opening of the PTP and the Bax alpha-induced permeability, and that the apoptotic mitochondria exhibit mixed properties between these model situations.

Human Kv1.6 current displays a C-type-like inactivation when re-expressed in cos-7 cells.

The human Kv1.6K(+) channel was functionally re-expressed in COS-7 cells at different levels. Voltage-activated K(+) currents are recorded upon cell membrane depolarization independently of the level of Kv1.6 expression. The current acquires a fast inactivation when Kv1.6 expression is increased. Inactivation was not affected by divalent cations or by extracellular tetraethylammonium. We have characterized the inactivation properties in biophysical terms. The fraction of inactivated current and the kinetics of inactivation are increased as the cell becomes more depolarized. Inactivated current can be reactivated according to a bi-exponential function of time. Additional experiments indicate that Kv1.6 inactivation properties are close to those of a conventional C-type inactivation. This work suggests that the concentration of Kv1.6 channel in the cell membrane strongly modulates the kinetic properties of Kv1.6-induced K(+) current. The physiological implications of these modifications are discussed.

Unfolding affects insect cell permeabilization by Bacillus thuringiensis Cry1C toxin.

Bacillus thuringiensis Cry toxins are efficient, environment-friendly biological insecticides. Their molecular mode of action on target insect cells remains largely unknown. The aim of this study was to investigate the relation between the conformational state of the Cry1C toxin and its ionophoric activity on live Sf9 cells of Spodoptera frugiperda, a target insect for this protein. Potassium ion movement induced by Cry1C across the cell membrane was measured with a fluorescent assay developed previously and the conformation of the toxin was studied using tryptophan spectroscopy. Following treatment with 4 M guanidinium hydrochloride, which resulted in the unfolding of its N-terminal half, the toxin retained its full capacity to permeabilize the cells while the fully unfolded toxin did not induce potassium leakage. Therefore, permeabilization of Sf9 cells by Cry1C requires the integrity of the C-terminal half of the toxin and may depend on an initial unfolding step provided by the acidic environment of the cells.

Inactivating properties of recombinant ROMK2 channels expressed in mammalian cells.

Biophysical properties of ROMK2 channel were investigated at physiological temperature, after reexpression of the recombinant ROMK2 protein in a mammalian cell expression system (COS-7). We observed that ROMK2 induced an inwardly rectifying K(+) current whether polyvalent cations were present or not. Above +10 mV, ROMK2-induced current exhibited a voltage- and time-dependent decay, consistent with an inactivation process. Inactivation of ROMK2-induced current was also seen in inside out patch from ROMK2-expressing Xenopus oocyte. In COS-7 cells, inactivation was found to account for most of the inward rectification. Mg(2+) and spermine modulated rectification by accelerating inactivation kinetics independently of membrane potential. These results establish for the first time ROMK2 properties in a mammalian cell expression system.

Transgenic mice overexpressing human KvLQT1 dominant-negative isoform. Part I: Phenotypic characterisation.

OBJECTIVES: The KCNQ1 gene encodes the KvLQT1 potassium channel, which generates in the human heart the slow component of the cardiac delayed rectifier current, I(Ks). Mutations in KCNQ1 are the most frequent cause of the congenital long QT syndrome. We have previously cloned a cardiac KCNQ1 human isoform, which exerts a strong dominant-negative effect on KvLQT1 channels. We took advantage of this dominant-negative isoform to engineer an in vivo model of KvLQT1 disruption, obtained by overexpressing the dominant-negative subunit under the control of the alpha-myosin heavy chain promoter. RESULTS: Three different transgenic lines demonstrated a phenotype with increasing severity. Functional suppression of KvLQT1 in transgenic mice led to a markedly prolonged QT interval associated with sinus node dysfunction. Transgenic mice also demonstrated atrio-ventricular block leading to occasional Wenckebach phenomenon. The atrio-ventricular block was associated with prolonged AH but normal HV interval in His recordings. Prolonged QT interval correlated with prolonged action potential duration and with reduced K(+) current density in patch-clamp experiments. RNase protection assay revealed remodeling of K(+) channel expression in transgenic mice. CONCLUSIONS: Our transgenic mouse model suggests a role for KvLQT1 channels not only in the mouse cardiac repolarisation but also in the sinus node automaticity and in the propagation of the impulse through the AV node.

Ca2+-sensitive cytosolic nucleases prevent efficient delivery to the nucleus of injected plasmids.

BACKGROUND: Efficient gene delivery by synthetic vectors is a major challenge in gene therapy. However, inefficient nuclear delivery of cDNA is thought to be a major limiting step in gene transfer using non-viral vectors. It is commonly thought that, in the cytosol, cDNA has to be released from its vector before importation to the nucleus. The stability of naked cDNA in the cytoplasm is not well established. METHODS: cDNA plasmids, either free or complexed with poly(ethyleneimine) (PEI), were microinjected into the cytoplasm of mammalian cells and their turnover was assessed by fluorescence in situ hybridization (FISH). Incubations of cDNA plasmids in cytosolic extracts were also performed. RESULTS: FISH experiments showed that naked cDNA rapidly fade with time when injected into the cytosol. Fading was not observed when naked cDNA plasmids were injected into the nucleus. Incubation of naked cDNA in a cytosolic fraction isolated from mammalian cells reproduced cDNA degradation as observed in microinjection experiments. Nuclease inhibitors, including aurin tricarboxylic acid or Zn2+, prevented in vitro cDNA degradation. The cytosolic nuclease activity was optimal at physiological pH and physiological Ca2+ concentration. By contrast, it was insensitive to Mg2+ or Na+ concentrations. Finally, cDNA complexation with PEI or addition of oligonucleotides prevented in vitro cDNA degradation. CONCLUSION: Altogether, these experiments suggest that cDNA digestion by cytosolic nucleases occur when the decomplexed transgene is present in the cytosol. We propose that the inefficient transfer of cDNA into the nucleus during transfection with synthetic vectors may result from rapid digestion of naked cDNA by a Ca2+-sensitive cytosolic nuclease.

Patch-clamp study of liver nuclear ionic channels reconstituted into giant proteoliposomes.

Nuclear ionic channels (NICs) represent ubiquitous structures of living cells, although little is known about their functional properties and encoding genes. To characterize NICs, liver nuclear membrane vesicles were reconstituted into either planar lipid bilayers or proteoliposomes. Reconstitution of nuclear envelope (NE) vesicles into planar lipid bilayer proceeded with low efficiency. NE vesicle reconstitution into proteoliposomes led to NIC observations by the patch-clamp technique. Large conductance, voltage-gated, K(+)-permeant and Cl(-)-permeant NICs were characterized. An 80-105-pS K(+)-permeant NIC with conducting sub-state was also recorded. Our data establish that NICs can be characterized upon reconstitution into giant proteoliposomes and retain biophysical properties consistent with those described for native NICs.

Ca2+ depletion and inositol 1,4,5-trisphosphate-evoked activation of Ca2+ entry in single guinea pig hepatocytes.

Store-operated Ca(2+) entry was investigated by monitoring the Ca(2+)-dependent K(+) permeability in voltage-clamped guinea pig hepatocytes. In physiological conditions, intracellular Ca(2+) stores are discharged following agonist stimulation, but depletion of this stores can be achieved using Ca(2+)-Mg(2+)-ATPase inhibitors such as 2,5-di(tert-butyl)-1,4-benzohydroquinone and thapsigargin. The effect of internal Ca(2+) store depletion on Ca(2+) influx was tested in single cells using inositol 1,4,5-trisphosphate (InsP(3)) release from caged InsP(3) after treatment of the cells with 2, 5-di(tert-butyl)-1,4-benzohydroquinone or thapsigargin in Ca(2+)-free solutions. We show that the photolytic release of 1-d-myo-inositol 1,4-bisphosphate 5-phosphorothioate, a stable analog of InsP(3), and Ca(2+) store depletion have additive effects to activate a high level of Ca(2+) entry in single guinea pig hepatocytes. These results suggest that there is a direct functional interaction between InsP(3) receptors and Ca(2+) channels in the plasma membrane, although the nature of these Ca(2+) channels in hepatocytes is unclear.

Kinetic properties of the channels formed by the bacillus thuringiensis insecticidal crystal protein Cry1C in the plasma membrane of Sf9 cells.

Spectrofluorimetric measurements were conducted to quantify, in real-time, membrane permeability changes resulting from the treatment of Sf9 insect cells (Spodoptera frugiperda, Lepidoptera) with different Bacillus thuringiensis Cry insecticidal proteins. Coumarin-derived CD222 and Merocyanin-540 probes were respectively used to monitor extracellular K(+) and membrane potential variations upon Sf9 cells incubation with Cry toxins. Our results establish that Cry1C induces, after a delay, the depolarization of the cell membrane and the full depletion of intracellular K(+). These changes were not observed upon Sf9 cells treated with Cry1A family toxins. Both the rate of the K(+) efflux and the delay before its onset were dependent on toxin concentration. Both parameters were sensitive to temperature but only the delay was affected by pH. Cry1C-induced K(+) efflux was inhibited by lanthanum ions in a dose-dependent manner. This study provides the first kinetic and quantitative characterization of the ion fluxes through the channels formed by a Cry toxin in the plasma membrane of a susceptible insect cell line.

Real-time fluorimetric analysis of gramicidin D- and alamethicin-induced K+ efflux from Sf9 and Cf1 insect cells.

Gramicidin D and alamethicin are pore-forming peptides which exhibit lethal properties against a large spectrum of cells. Despite a wealth of experimental data from artificial membranes, the time course and quantitative analysis of the activity of these ionophores are not well described in living cells. In the present study, the newly described fluorescent dye CD-222 was used to monitor extracellular potassium ion concentration and report the effects of these antibiotics on the K+ permeability of the plasma membrane of Spodoptera frugiperda (Sf9) and Choristoneura fumiferana (Cf1) insect cells. Both peptides induced a rapid efflux of intracellular K+ as a consequence of ion channel formation in the cell membrane. K+ efflux began without any measurable delay. While the final extracellular K+ concentration was unaffected by ionophore concentration, the rate of K+ efflux was dose dependent. Using a model describing the partition of the peptides in lipid membranes, the K+ efflux kinetic parameters were determined for both cell types and both pore formers. The proposed stoichiometry for the channel formed by gramicidin in living cells is in good agreement with the two-monomers model based on data from artificial membrane systems. The K+-permeable channel formed by alamethicin in insect cells appears to involve three monomers.

Does the nuclear envelope contain two types of ligand-gated Ca2+ release channels?

The nuclear envelope is composed of two membranes deliminating a perinuclear space which displays functional properties similar to those of a Ca2+-storing compartment. ATP-driven Ca2+ uptake and InsP3-induced Ca2+ release processes have been described in isolated nuclei. Recently, it was reported that cADP-ribose and InsP3 can trigger a nucleoplasmic Ca2+ increase. It was hypothesized that the inner nuclear membrane possesses Ca2+ channels that are regulated by ryanodine or InsP3. Radio-ligand binding assays and Western blot experiments were performed in order to investigate their presence in sheep cardiac and rat liver nuclear envelopes. Ryanodine receptors (RyR) were not detected in liver nuclear envelopes by either binding assay or Western blot analysis. However, cardiac nuclear envelopes were found to retain a very low level of specific ryanodine binding, which was not detected on immuno-blots obtained with three types of isoform-specific RyR antibodies. In contrast, nuclear InsP3-binding sites were consistently detected in both cardiac and liver nuclear envelopes. Altogether, these results provide evidence for the major contributor InsP3-gated Ca2+ channels in control of Ca2+ release from the perinuclear space in liver and cardiac cells.

3':5'-cyclic guanosine monophosphate (cGMP) potentiates the inositol 1,4,5-trisphosphate-evoked Ca2+ release in guinea-pig hepatocytes.

The effect of cGMP on noradrenaline-induced intracellular Ca2+ mobilization was investigated in whole-cell voltage-clamped guinea-pig hepatocytes. Treatment of the cells with 8-Br-cGMP (1-500 microM) resulted in an increase in the sensitivity of the cells to noradrenaline and to inositol 1,4,5-trisphosphate (InsP3) photo-released from caged InsP3. The positive effect of 8-Br-cGMP on the Ca2+ release evoked by Ca(2+)-mobilizing agonists or InsP3 was blocked by a protein kinase G (PKG; cGMP-dependent protein kinase) inhibitor, the RP-8-(4-chlorophenylthio)guanosine 3':5'-monophosphorothioate. 8-Br-cGMP affected neither the basal InsP3 concentration nor the noradrenaline-induced production of InsP3. In permeabilized hepatocytes, the dose-response curve for InsP3-induced Ca2+ release was shifted to the left in the presence of 8-Br-cGMP. Furthermore, the treatment with 8-Br-cGMP did not affect the Ca2+ content of the InsP3-sensitive Ca2+ stores. These results indicate that intracellular cGMP potentiates the noradrenaline-induced Ca2+ response by enhancing Ca2+ release from the intracellular Ca2+ stores. We suggest that cGMP increases the apparent affinity of InsP3 receptors for InsP3 in guinea-pig hepatocytes probably by phosphorylation via the activation of PKG.

In vivo and in vitro studies of the inhibition of the channel activity of colicins by gadolinium.

The primary effects of the ionophoric colicins A, E1 and B on Escherichia coli cells include triggering an efflux of cytoplasmic potassium, and a decrease of internal ATP as consequences of the opening of ionic channels in the cytoplasmic membrane. We report that micromolar concentrations of gadolinium and other members of the lanthanide family inhibited the efflux of potassium and the ATP decrease and that the cells recovered both ATP and potassium within a few minutes. Gadolinium, in the same concentration range also efficiently inhibited the channel activity of colicins A, E1, B and of the isolated channel-forming domain of colicin A in planar lipid bilayers. Colicin N was much less sensitive to the trivalent ion in planar lipid bilayers, consistent with the lack of effect of gadolinium on this colicin in vivo. Our data suggest that lanthanide ions act by direct binding to the colicin molecule and that this binding affects both its single-channel conductance and gating behaviour.

Mode of Action of Nisin Z against Listeria monocytogenes Scott A Grown at High and Low Temperatures.

Nisin Z, a natural nisin variant, was recently isolated from Lactococcus lactis subspecies lactis NIZO 22186. The gene for this lantibiotic, designated nisZ, has been cloned, and its nucleotide sequence was found to be identical to that of the precursor nisin gene with the exception of a single mutation resulting in the substitution of Asn-27 for His-27 in the mature polypeptide (J. W. M. Mulders, I. J. Boerrigter, H. S. Rollema, R. J. Siezen, and W. M. de Vos, Eur. J. Biochem. 201:581-584, 1991). A K electrode was used to investigate the effect of various environmental parameters on the action of nisin Z against Listeria monocytogenes. Addition of nisin Z resulted in immediate loss of cell K, depolarization of the cytoplasmic membrane, inhibition of respiratory activity, and hydrolysis and partial efflux of cellular ATP. The action of nisin Z was optimal at pH 6.0 and was significantly reduced by di- and trivalent cations. The lanthanide gadolinium (Gd) was an efficient inhibitor and prevented nisin Z activity completely at a concentration of 0.2 mM. Nisin Z-induced loss of cell K was reduced at low temperatures, presumably as a result of the increased ordering of the lipid hydrocarbon chains in the cytoplasmic membrane. In cells grown at 30 degrees C, the action of nisin Z was prevented below 7 degrees C, whereas in cells grown at 4 degrees C nisin Z was able to induce K leakage at this low temperature.

Colicin A and the Tol proteins involved in its translocation are preferentially located in the contact sites between the inner and outer membranes of Escherichia coli cells.

Colicin A is a bacterial toxin which forms channels in the cytoplasmic membrane of Escherichia coli. Its translocation through the envelope requires the participation of bacterial proteins encoded by the tolQ, -R, -A, and -B genes. Overproduction of the Tol proteins decreased the time needed for colicin A translocation and increased the number of channels formed in vivo. Cells overproducing radioactively labeled Tol proteins and containing or not colicin A were fractionated. The Tol proteins were mainly recovered in the inner membrane and in the contact sites between the two membranes. The presence of colicin A increased the specific radioactivity of the Tol proteins in the contact sites. Our data suggest that the Tol proteins form a complex of definite stoichiometry in the membranes and that colicin A is associated to this complex upon channel formation. We discuss the possibility that the channel activity determined in vivo is due to the colicin A-Tol proteins complex.

Phosphate efflux through the channels formed by colicins and phage T5 in Escherichia coli cells is responsible for the fall in cytoplasmic ATP.

Previous studies have shown that channel formation in the cytoplasmic membrane of Escherichia coli by colicin A and phage T5 leads to an efflux of cytoplasmic potassium and to a membrane depolarization. Here we show that upon opening of these channels, the intracellular ATP concentration is decreased to 10% of its original value in < 5 min. ATP is not found in the external medium, but is hydrolyzed in the cytoplasm into ADP and AMP. The rate of ATP hydrolysis depends on the number of channels and on their activity. ATP hydrolysis takes place if the F1F0-ATPase is absent or inhibited. Depolarization of the inner membrane is not the main cause of ATP hydrolysis. Opening of the phage and colicin channels also leads to an efflux of inorganic phosphate. Conditions that prevent the efflux of phosphate (i.e. depolarization of the cells and high external phosphate concentration) prevent ATP hydrolysis. We propose that ATP is hydrolyzed as a consequence of a shift in the ATP equilibrium due to the efflux of phosphate through the channels. The consequences for the cells of this ATP depletion are discussed.