The Relation between Membrane Potential and the Transport Activity of Systems a and L in Plasma Membrane Vesicles of the Ehrlich Cell

Plasma membrane vesicles isolated from Ehrlich ascites tumor cells have been used to investigate the role of the transmembrane potential in the energetics of Systems A and L. As expected, Na⁺-dependent System A was responsive to changes in membrane potential. System L activity, as measured by transport of 2-aminonorbornane-2-carboxylic acid (BCH), was shown to be Na⁺-independent and was not altered by changes in the membrane potential. The combination of valinomycin and nigericin decreased accumulation of MeAIB but not that of BCH. The presence of nigericin alone caused a significant decrease in uptake by System A and a decrease in uptake by System L to a lesser degree. The inhibitory action of nigericin might reflect its ability to dissipate the Na⁺ gradient rather than an effect on K⁺ or H⁺ flows. The results indicate that modes of energization not produced through the transmembrane potential must account for any uphill operation of System L.     

Activity of the Electrogenic Pump in Chara corallina as Inferred from Measurements of the Membrane Potential, Conductance, and Potassium Permeability

The effects of various inhibitors on the membrane potential, resistance, and K⁺ permeability of Chara corallina were measured, providing evidence that there is an electrogenic pump in the membrane. It was found that: (a) 5.0 μm carbonyl cyanide m-chlorophenyl hydrazone depolarizes the membrane potential and increases the membrane resistance. This inhibition is faster in the dark than in the light but the extent of inhibition is the same in both cases. (b) Fifty μm dicyclohexylcarbodiimide increases the resistance and the K⁺ permeability and depolarizes the membrane to a diffusion potential mainly controlled by K⁺. (c) Forty μm diethylstilbestrol and 0.1 mm 2,4-dinitrophenol increase the resistance and depolarize the potential to a value given by the Goldman diffusion equation. (d) Both 3-(3,4-dichlorophenyl)-1,1-dimethylurea and darkness (at pH 6) cause the membrane resistance to increase but neither has a large effect on the potential. 3-(3,4-dichlorophenyl)-1,1-Dimethylurea increases K⁺ permeability while darkness decreases it.     

Light-Triggered Changes of Membrane Potential in Cells of Anthoceros punctatus and their Relation to Activation of Chloroplast ATPase

Post-illumination transients of the membrane potential wererevealed in cells of Anthoceros punctatus upon short (1–2s) irradiation with photosynthetically active light. An initialfast depolarization of the cell by 20–30 mV after a lagperiod of 2 s and a subsequent slow repolarization were recordedwith micro-electrodes positioned both in the chloroplast andin transparent parts of the cell. The potential changes of similarkinetics were also observed upon continuous illumination. Post-illuminationpotential changes were abolished by 3-(3, 4-dichlorophenyl)-l,l-dimethylurea and dicyclohexylcarbodiimide and were stimulatedby the addition of NH₄C1. It is assumed that the light-triggeredpotential change across the plasmalemma of A. punctatus aredetermined by the light activation of chloroplast ATPase. Thisassumption is further supported by observations of post-illuminationtransient increase of the chlorophyll fluorescence in preparationsof A. punctatus. Key words: Cell membrane potential, Chloroplast, Photosynthesis     

Membrane Potential of Cultured Carrot Cells in Relation to the Synthesis of Anthocyanin and Embryogenesis

Membrane potentials of cultured carrot cells in culture mediumwere about –40 mV and did not change with addition ofsalts of addition (or depletion) of 2,4-dichlorophenoxyaceticacid (2,4-D). When the measurement was performed in the testmedium (containing low concentration of salts), the values werewidely distributed (from –60 to –110mV) and changedlargely with external concentration of K⁺ but not Mg²⁺ nor Ca²⁺.When the cells were fractionated by Ficoll density gradientcentrifugation, the membrane potential of the cells of higherdensity (> 14% Ficoll) was about –150 mV in the testmedium and did not change during embryogenesis with depletionof 2,4-D. The membrane potential of cells of lower density (bandingbetween 6– 10% Ficoll) was less negative (– 60 to– 110 mV) in the test medium. When these cells were transferredand cultured in medium containing zeatin but lacking 2,4-D,the membrane potential was shifted negatively by about 15 mVprior to anthocyanin synthesis. When 2,4-D was added to anthocyanin-synthesizingcells in the medium containing zeatin, a transient hyperpolarizationand subsequent depolarization of the membrane were observedprior to the inhibition of anthocyanin synthesis. (Received October 22, 1987; Accepted April 20, 1988)     

Egg Membrane Lytic Activity of Sperm Extract and its Significance in Relation to Sperm Entry in Hydroides hexagonus (Annelida)

Previous electron microscope studies indicated that the individual spermatozoön of Hydroides hexagonus forms a hole in the vitelline membrane by means of lysis. Other observations established that the hole is real, being visible in living material during sperm entry. During the present investigation sea water extracts from frozen-thawed sperm were tested for lytic effect on the membrane. In normal living eggs the membrane appears as a single thick envelope, but in electron micrographs of sections it is seen to consist of a narrow outer border layer, a wide principal or middle layer, and a narrow inner border layer. After immersion in sperm extract the outer border layer elevates but does not dissolve, the middle layer liquefies and disappears, and the inner border layer seems not to change. This is interpreted as lysis of the middle layer. The extract exerted the same effect on fertilized and unfertilized eggs. In electron micrographs the sections treated with extract greatly resemble that part of the membrane which has been penetrated by the individual spermatozoön. It is concluded that the individual spermatozoön, too, exerts a lytic effect. Together, the present and two earlier studies are considered clearly to demonstrate that in Hydroides the individual spermatozoön does indeed make an entry hole in the egg membrane by applying lytic material to that part of the membrane in its own vicinity.     

Effects of Light and Bicarbonate on Membrane Potential in Potamogeton schweinfurthii (Benn)

Measurements have been made of photosynthesis by submerged leavesof the aquatic angiosperm, Potamogeton schweinfurthii, and ofmembrane potential differences between the interior of leafcells and various media. Bicarbonate may be absorbed and usedfor photosynthesis with concomitant export of hydroxyl ionshowever much molecular carbon dioxide is also present and beingabsorbed. The green cells are temporarily depolarized upon illuminationand hyperpolarized on darkening. These potential changes areassociated with absence and presence of bicarbonate and aretentatively interpreted in terms of active transport mechanismsfor bicarbonate and hydroxyl ions.     

Membrane Potential Fluctuations Determine the Precision of Spike Timing and Synchronous Activity: A Model Study

It is much debated on what time scale information is encoded by neuronal spike activity. With a phenomenological model that transforms time-dependent membrane potential fluctuations into spike trains, we investigate constraints for the timing of spikes and for synchronous activity of neurons with common input. The model of spike generation has a variable threshold that depends on the time elapsed since the previous action potential and on the preceding membrane potential changes. To ensure that the model operates in a biologically meaningful range, the model was adjusted to fit the responses of a fly visual interneuron to motion stimuli. The dependence of spike timing on the membrane potential dynamics was analyzed. Fast membrane potential fluctuations are needed to trigger spikes with a high temporal precision. Slow fluctuations lead to spike activity with a rate about proportional to the membrane potential. Thus, for a given level of stochastic input, the frequency range of membrane potential fluctuations induced by a stimulus determines whether a neuron can use a rate code or a temporal code. The relationship between the steepness of membrane potential fluctuations and the timing of spikes has also implications for synchronous activity in neurons with common input. Fast membrane potential changes must be shared by the neurons to produce synchronous activity.     

水分胁迫对巴西香蕉幼苗水分状况、质膜透性和根系活力的影响

最适宜的土壤水分含量是田间持水量的71%～80%.     

Structural Basis for the Biological Effects of Pr(III) Ions: Alteration of Cell Membrane Permeability

The biological effects of rare-earth ions on the organism have been studied using Pr³⁺ as a probe ion and Escherichia coli cell as a target. Atomic force microscopy (AFM) observation of the surface of E. coli cells shows that the presence of Pr³⁺ substantially changes the structure of the outer membrane. By induced coupled plasma-mass spectrometry (ICP-MS), more Cu²⁺ was found in the cells grown in the presence of Pr³⁺, indicating changes of cell permeability. Using energy dispersive X-ray spectroscopy (EDX), Ca²⁺ is found on the outer surface of the original cell. It is proposed that Pr³⁺ can replace Ca²⁺ from the binding sites because of their close ionic radii and similar ligand speciality.     

Anion Selectivity of Slow Anion Channels in the Plasma Membrane of Guard Cells (Large Nitrate Permeability)

Closing of stomatal pores in the leaf epidermis of higher plants is mediated by long-term release of potassium and the anions chloride and malate from guard cells and by parallel metabolism of malate. Previous studies have shown that slowly activating anion channels in the plasma membrane of guard cells can provide a major pathway for anion efflux while also controlling K+ efflux during stomatal closing: Anion efflux produces depolarization of the guard cell plasma membrane that drives K+ efflux required for stomatal closing. The patch-clamp technique was applied to Vicia faba guard cells to determine the permeability of physiologically significant anions and halides through slow anion channels to assess the contribution of these anion channels to anion efflux during stomatal closing. Permeability ratio measurements showed that all tested anions were permeable with the selectivity sequence relative to Cl- of NO3- > Br- > F- ~ Cl- ~ I- > malate. Large malate concentrations in the cytosol (150 mM) produced a slow down-regulation of slow anion channel currents. Single anion channel currents were recorded that correlated with whole-cell anion currents. Single slow anion channels confirmed the large permeability ratio for nitrate over chloride ions. Furthermore, single-channel studies support previous indications of multiple conductance states of slow anion channels, suggesting cooperativity among anion channels. Anion conductances showed that slow anion channels can mediate physiological rates of Cl- and initial malate efflux required for mediation of stomatal closure. The large NO3- permeability as well as the significant permeabilities of all anions tested indicates that slow anion channels do not discriminate strongly among anions. Furthermore, these data suggest that slow anion channels can provide an efficient pathway for efflux of physiologically important anions from guard cells and possibly also from other higher plant cells that express slow anion channels.     

Effect of R-(-)-Deprenyl and Harmaline on Dopamine- and Peroxynitrite-Induced Membrane Permeability Transition in Brain Mitochondria

The present study examined the effect of MAO inhibitors, deprenyl and harmaline, on the membrane permeability transition in brain mitochondria. Deprenyl, harmaline, and antioxidant enzymes (SOD and catalase) attenuated alteration of the swelling, membrane potential, cytochrome c release, and Ca²⁺ transport in mitochondria treated with dopamine. In contrast, deprenyl and harmaline did not reduce the peroxynitrite-induced change in membrane permeability. Deprenyl and harmaline inhibited the decrease in thioredoxin reductase activity and the thiol oxidation in mitochondria treated with dopamine but did not decrease the effect of peroxynitrite. Deprenyl and harmaline significantly decreased the formation of melanin from dopamine. The results suggest that deprenyl and harmaline may protect brain mitochondria against the toxic action of dopamine oxidation by the maintenance of thioredoxin reductase activity, inhibition of thiol oxidation, and inhibition of dopamine oxidation product formation. In contrast, MAO inhibitors may not defend brain mitochondria against damaging action of peroxynitrite.     

Changes in the Sterol Composition of the Plasma Membrane Affect Membrane Potential,Salt Tolerance and the Activity of Multidrug Resistance Pumps in Saccharomyces cerevisiae

We investigated the impact of the deletions of genes from the final steps in the biosynthesis of ergosterol (ERG6, ERG2, ERG3, ERG5, ERG4) on the physiological function of the Saccharomyces cerevisiae plasma membrane by a combination of biological tests and the diS-C₃(3) fluorescence assay. Most of the erg mutants were more sensitive than the wild type to salt stress or cationic drugs, their susceptibilities were proportional to the hyperpolarization of their plasma membranes. The different sterol composition of the plasma membrane played an important role in the short-term and long-term processes that accompanied the exposure of erg strains to a hyperosmotic stress (effect on cell size, pH homeostasis and survival of yeasts), as well as in the resistance of cells to antifungal drugs. The pleiotropic drug-sensitive phenotypes of erg strains were, to a large extent, a result of the reduced efficiency of the Pdr5 efflux pump, which was shown to be more sensitive to the sterol content of the plasma membrane than Snq2p. In summary, the erg4Δ and erg6Δ mutants exhibited the most compromised phenotypes. As Erg6p is not involved in the cholesterol biosynthetic pathway, it may become a target for a new generation of antifungal drugs.     

Disorders of System Brain Activity in Children with Motor (Expressive) Alalia

Motor alalia refers to a number of disorders of expressive speech that are caused by the dysfunction of cerebral structures in the period when the formation of the speech system is not complete. This form of speech disorder is considered as a language disorder characterized by a persistent disturbance of the assimilation of a system of linguistic units. The possible cause of deviations in the development of speech function in children is a disproportion in the levels of development of speech structures in the left and right hemispheres, and this temporary dominance is often associated with an increased activity in the right hemisphere. According to the results of electroencephalographic studies, in children aged five to six years, there are two types of changes of the bioelectric potential system interaction of the brain cortex. The disorders of the spatial organization of interregional EEG correlations are more pronounced in either the left or right hemispheres of the brain. Thus, motor alalia can be accompanied either by disturbances in the interaction between Broca’s and Wernicke’s areas of the left hemisphere, or between symmetrical areas of the right hemisphere.     

The Relation between the Structure of Coumarin and its Derivatives, and their Activity as Germination Inhibitors

A large number of substitution derivatives of coumarin wereexamined. In every case the activity was wholly or partiallyremoved by substitution. A number of growth regulators of the2:4-D type were examined. These acted as germination inhibitors,in some cases being more active than coumarin. It is concluded that the activity of coumarin as a germinationinhibitor is due to its specific structure, consisting of anunsaturated lactone linked to an unsubstituted benzene nucleus.Any change in this structure leads to the partial destructionof the activity as a germination inhibitor.     

Evaluation of Iron in Serum and Urine and their Relation with Thyroid Function in Female Goitrous Patients

In many developing countries, women are at high risk of goiter and iron deficiency anemia (IDA). Iron deficiency adversely affects thyroid metabolism and may decrease the efficiency of thyroid hormones in areas of endemic goiter. The aim of the present study was to compare the level of iron (Fe) in biological samples (serum and urine) and serum thyroid hormones, thyroid stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxin (FT4) of goitrous female patients (GFPs; n = 69) with those of nongoitrous women as control subjects (n = 117), age range 21–45 years. The biological samples were analyzed for Fe concentration using flame atomic absorption spectrophotometer, prior to microwave-assisted wet acid digestion. The validity and accuracy of the method was checked by the certified sample and with those obtained by conventional wet acid digestion method on the same CRM and real samples. The overall recoveries of Fe in serum and urine were found in the range of 97.2–98.6% of certified values. The results of this study showed that the mean values of Fe in serum and urine samples of GFPs were significantly reduced as compared to control subjects (p = 0.002 and p = 0.015, respectively). The mean values of FT3 and FT4 were found to be lower in GFPs than in the age-matched healthy control women; in contrast, high mean values of TSH were detected in GFPs (p = 0.003). There was a positive correlation between serum Fe concentration and TSH (r = 0.85, p = 0.01), FT3 (r = 0.95, p = 0.003), and FT4 levels (r = 0.98, p = 0.007) in GFPs. It was observed that iron deficiency is prevalent in GFPs, so the need of Fe supplementation will be required to improve the efficacy of thyroid metabolism in goitrous women.     

Mutational Analysis of the Integral Membrane Methyltransferase Isoprenylcysteine Carboxyl Methyltransferase (ICMT) Reveals Potential Substrate Binding Sites

The eukaryotic integral membrane enzyme isoprenylcysteine carboxyl methyltransferase (ICMT) methylates the carboxylate of a lipid-modified cysteine at the C terminus of its protein substrates. This is the final post-translational modification of proteins containing a CAAX motif, including the oncoprotein Ras, and therefore, ICMT may serve as a therapeutic target in cancer development. ICMT has no discernible sequence homology with soluble methyltransferases, and aspects of its catalytic mechanism are unknown. For example, how both the methyl donor S-adenosyl-l-methionine (AdoMet), which is water-soluble, and the methyl acceptor isoprenylcysteine, which is lipophilic, are recognized within the same active site is not clear. To identify regions of ICMT critical for activity, we combined scanning mutagenesis with methyltransferase assays. We mutated nearly half of the residues of the ortholog of human ICMT from Anopheles gambiae and observed reduced or undetectable catalytic activity for 62 of the mutants. The crystal structure of a distantly related prokaryotic methyltransferase (Ma Mtase), which has sequence similarity with ICMT in its AdoMet binding site but methylates different substrates, provides context for the mutational analysis. The data suggest that ICMT and Ma MTase bind AdoMet in a similar manner. With regard to residues potentially involved in isoprenylcysteine binding, we identified numerous amino acids within transmembrane regions of ICMT that dramatically reduced catalytic activity when mutated. Certain substitutions of these caused substrate inhibition by isoprenylcysteine, suggesting that they contribute to the isoprenylcysteine binding site. The data provide evidence that the active site of ICMT spans both cytosolic and membrane-embedded regions of the protein.     

Xylem Occlusions in the Fruit of Cacao (Theobroma cacao) and their Relation to Cherelle Wilt

The anatomy and distribution of the xylem of the fruit of cao(Theobroma cacao) has been investigated by injection and stainingtechniques. The physical symptoms of cherelle wilt (pod wilt), a physiologicalfruitthinning mechanism, have been shown to be caused by occlusionsin the xylem vessels of the fruit-stalk. The initiation of theseocclusions in thought to be associated with the oxidative activityof a cambial or meristermatic band of tissue, which forms newvascular tissue to the pericarp.     

Seasonal Depth-Related Gradients in Virioplankton: Lytic Activity and Comparison with Protistan Grazing Potential in Lake Pavin (France)

This study presents an original depth-related survey of virioplankton lytic activity in relation to prokaryotic production and potential protistan bacterivory in the deep (Z(max) = 92 m) meromictic volcanic Lake Pavin (Massif Central, France). The sampling strategy was designed to be representative of the physico-chemical gradients of the water column of the lake, and of the seasonal variability as well, i.e. 12 different depths sampled in triplicates from April to December 2005. In the space, viral lytic activity estimated from the frequency of visibly infected prokaryotic cells and from burst size over the study period generally decreased with depth. This was viewed as a paradox compared to the abundances of viruses and prokaryotes and to the prokaryotic production which increased with depth. The seasonal variability in viral lytic activity was correlated with prokaryotic variables (abundance and production) in the deepest waters, i.e. from the hypolimnion downwards. Compared to previous studies known from the mixolimnion, we conclude that the deep waters in Lake Pavin represent an exclusive environment for heterotrophic prokaryotes whose seasonal activity offers an optimal and unique resource for thriving viral communities, some of which may be typical, endemic to the ambient dark, cold and stable deep water masses. Overall, the main findings in the present study get well around a previous statement that the ecology of the deepest waters of Lake Pavin is essentially driven by the dark viral loop (dissolved organic matter-prokaryotes-viruses) processes, which can sequester organic matters and nutrients for a long-lived turnover time. This is in agreement with recent demonstrations from marine systems that meso- and bathypelagic waters are optimal environments for viral survival and proliferation.     

Tetramethyl Rhodamine Methyl Ester (TMRM) is Suitable for Cytofluorometric Measurements of Mitochondrial Membrane Potential in Cells Treated with Digitonin

A new method for cytofluorometric analysis of mitochondrial membrane potential has been developed by using TMRM as a cationic, mitochondrial selective probe. The method is based on limited treatment of cultured cells with digitonin which permeabilises the plasma membrane and leaves mitochondria intact. The resulting signal of TMRM-stained cells thus represents only the probe accumulated in mitochondria. Fibroblasts and cybrids were used as a model cell systems and optimal conditions for digitonin treatment and staining by TMRM were described. The TMRM signal collapsed by valinomycin, KCN and antimycin A and FCCP titration was used to gradually lower and characterise the stability of . The method is suitable for sensitive measurement of in different types of cultured cells.