Effect of phenoxyethanol on the permeability of Escherichia coli NCTC 5933 to inorganic ions.

Concentrations of phenoxyethanol which retarded the growth rate of Escherichia coli NCTC 5933 in nutrient broth, stimulated the rates of respiration and total oxygen uptake of cell suspensions with glucose as carbon source, and were able to dissipate artificially induced membrane proton gradients. In cells with repressed oxidative phosphorylating activity, no stimulation of respiration was observed. These actions were characteristic of uncouples of oxidative phosphorylation. Similar concentrations of the drug caused additional increased permeability of the cytoplasmic membrane to K+ but not to Li+, Na+, Ca++, Mg++, NO-3, Cl-, So--4, or PO---4. Drug induced permeability of the membrane to protons and potassium ions were not found to be directly coupled.     

Effect of acetazolamide on salivary excretion of inorganic ions in sheep

The salivary excretion of inorganic ions in sheep was studied parallel with infusion of salt solutions of different composition through the temporary isolated rumen cavityin vivo. The amount of Na⁺ excreted with saliva decreases by 15–55% after an intravenous loading with acetazolamide (50 mg/kg of animal weight) and by 25–55%, of K⁺, which represents a part of the ion excretion with participation of H⁺ exchanges. The Na⁺ excretion that is not inhibited by acetazolamide in sheep is about 40 mmol/10 kg of exchange mass per 1 h in all experiments with loading.     

Effect of calcium ions on potassium conductivity of latrotoxin channels

It has been shown that inhibition of potassium current through latrotoxin channels by calcium ions is followed by electrostatic interaction of these ions with a total charge on the mouth of the channel.     

Ca ions in regulation of the permeability and mechanical properties of intercellular contacts of small intestinal epithelium]

The role of Ca in regulating passive permeability of alkaline cations is investigated. As it has been shown, the pathway of permeability are intercellular junctions [9-10]. An attempt was made to use permeability parameters for characterizing intercellular junctions. Forms of Ca binding and the nature of site, that discriminated ion permeation are evaluated. To develop the studies of functional peculiarities of intercellular junctions, the role of Ca in regulating the mechanical properties of intercellular junction of small intestine epithelia are investigated.     

Effects of inorganic salts on tissue permeability

Inorganic solutes are shown to alter the permeability of root and leaf tissues. Experiments with beet root tissues reveal that CaCl(2) decreases leakage of betacyanin from the tissue, that (NH(4))(2)SO(4) increases leakage, and that each salt can relieve the effects of the other. A comparison of cations and anions shows a range of effects with the various solutes. Experiments with Rumex obtusifolius L. leaf discs reveal that whereas CaCl(2) defers the development of senescence, (NH(4))(2)SO(4) hastens senescence and increases the leakage of materials out of the leaf discs. The solute effect on Rumex obtusifolius L. is prevented by gibberellin. CaCl(2) can relieve the (NH(4))(2)SO(4) effect. The results are interpreted as indicating that the inorganic solutes may serve to alter the permeability of membranes through alterations of interactions between water and macromolecules in the tissues; the interpretation is consistent with the evidence for opposite effects of Ca and NH(4), the effective concentrations being about 10(-3)m, and the reversibility of the effects of one solute by another of opposite stabilization-destabilization effect.     

Effect of the anthraquinones emodin and physcion on availability of selected soil inorganic ions

The effects of emodin and physcion, two anthraquinones involved in Polygonum sachalinense allelopathy, were studied in soils amended with 5, 10 and 15 mg 100 g^-1 soil of each compound, and with their mixtures. Recovery of each compound and its effects on availability of soil Mn⁺⁺, Na⁺, K⁺, Mg⁺⁺, Ca⁺⁺ and PO₄^3- were monitored. Total phenolic content of each soil was determined to study the role of degraded phenolics. Soil amended with 5 mg of emodin and physcion gave maximum recovery of the two anthraquinones. Soil amended with different amounts of two anthraquinones and their mixture had significant lower values for pH compared to control. In general, both anthraquinones affect availability of soil inorganic ions. Compared to unamended control soil, a significant decrease in Mn⁺⁺ availability, and an increase in Na⁺ and K⁺ availability when emodin and physcion were added to the soil was observed. A correlation among soil inorganic ions, relative recovery of two compounds, and total phenolic content of amended soils was observed. Results indicate that emodin and physcion influence the availability of soil inorganic ions. The significance of the effect of allelopathic compounds on soil inorganic ions is discussed.     

Biological role of connexin intercellular channels and hemichannels

Gap junctions (GJ) and hemichannels (HC) formed from the protein subunits called connexins are transmembrane conduits for the exchange of small molecules and ions. Connexins and another group of HC-forming proteins, pannexins comprise the two families of transmembrane proteins ubiquitously distributed in vertebrates. Most cell types express more than one connexin or pannexin. While connexin expression and channel activity may vary as a function of physiological and pathological states of the cell and tissue, only a few studies suggest the involvement of pannexin HC in acquired pathological conditions. Importantly, genetic mutations in connexin appear to interfere with GJ and HC function which results in several diseases. Thus connexins could serve as potential drug target for therapeutic intervention. Growing evidence suggests that diseases resulting from HC dysfunction might open a new direction for development of specific HC reagents. This review provides a comprehensive overview of the current studies of GJ and HC formed by connexins and pannexins in various tissue and organ systems including heart, central nervous system, kidney, mammary glands, ovary, testis, lens, retina, inner ear, bone, cartilage, lung and liver. In addition, present knowledge of the role of GJ and HC in cell cycle progression, carcinogenesis and stem cell development is also discussed.     

Effect of integral proteins upon bilayer permeability to small ions

We have modelled the effect of integral proteins upon the permeability of a lipid bilayer membrane to small ions. Our intention is to predict the temperature-and protein concentration-dependence of the relative ionic diffusion coefficient if it is assumed that the ions diffuse entirely through the lipid regions of the membrane, and do not cross the bilayer either by moving through the protein or along its hydrophobic surface. We used models of lipid-protein bilayers that have been used successfully before, together with a modification of the (protein-free) permeability mechanism of Kanchisa, Tsong, Cruzeiro-Hansson and Mouritsen (KTCM). We used Monte Carlo techniques to simulate the thermodynamics and permeability of the membrane because such a calculation, which depends upon spatial and time correlations, cannot be done using a mean field approximation. We took the protein to be analogous to bacteriorhodopsin and calculated the relative diffusion coefficients, R, of small ions through a DMPC bilayer containing such proteins. We found that although there is only a small change in R when T > T _m , R can change by an order of magnitude, depending upon the protein concentration, for T < T _m . We showed that regions of largest lipid area fluctuations and, hence, compressibility occur (i) at the interfaces between regions (which may be very small and not macroscopic phases) of extended-chain and excited-chain lipids, thus showing the similarity between this model and the KTCM model, and (ii) in regions where the temperature is close to T _m but the lipids are prevented from becoming ordered because of the proximity of proteins which try to keep them in their excited-chain states. We have plotted lipid fluctuation and ionic permeability maps to show which regions of the membrane display the largest permeability, and we show how these regions change as a function of temperature. Offprint requests to D. A. Pink     

Effect of the respiratory chain redox state on mitochondrial membrane permeability for K+ ions]

Transport of Pi into mitochondrial matrix induces K+-permeability of the membranes, which results from the addition of DNP. This induction of K+ efflux is eliminated by some agents causing the respiratory chain reduction (e.g. succinate, rotenone, antimycin A). It was shown that the abolition of the membrane potential is not sufficient for K+ efflux induction. The latter process is necessary for the energy-linked formation of the K+-transporting system. The lipid fraction containing lecithin and monophosphoinositol was extracted from the mitochondria after preincubation with Pi. The artificial bilayer membranes formed from these lipids are permeable for K+.     

Effect of magnesium ions on the thermostability of inorganic pyrophosphatase from baker's yeast]

The interaction of magnesium ions with inorganic pyrophosphatase from baker's yeast was studied by means of heat denaturation. The heat inactivation of this enzyme is a biphasic process. The velocities in the initial range and in the subsequent slower part of inactivation are diminished with rising Mg2+ concentration in the inactivation assay. A model is proposed which describes this behavior. It is assumed that two enzyme conformations exist in equilibrium whose conversion rates correspond to the inactivation rate in its order of magnitude. The equilibrium is shifted by Mg2+. The two enzyme species differ in their Mg2+ binding behavior as evidenced by differences in the half-saturation constants and the cooperativity of the binding. The same conclusions are drawn from the fluorimetric measurement of denaturation of inorganic pyrophosphatase. Besides, an additional Mg2+ binding site is demonstrable, the saturation of which obviously leads to stabilisation of part of the enzyme structure without protecting it against loss of enzymatic activity. With the same method the labilizing effect of Zn2+ on the structure of the inorganic pyrophosphatase from baker's yeast was studied.     

Calcium permeability of ligand-gated channels

Ligand-gated channels activated by excitatory neurotransmitters: glutamate, acetylcholine, ATP or serotonin are cation channels permeable to Ca2+. Molecular cloning revealed a large variety of the ligand-gated channel subunits differentially expressed in mammalian brain. Many of them have different Ca2+ permeability providing immense diversity in Ca2+ entry mediated by ligand-gated channels during synaptic transmission. Functional analysis of cloned channels allowed to identify structural elements in the pore forming regions determining Ca2+ permeability for many types of ligand-gated channels. The functional role of the Ca2+ entry mediated by various ligand-gated channels in mammalian central nervous system is less understood. The studies reviewed in this article provide information about known structural determinants of Ca2+ permeability of the ligand-gated channels and the role of this particular pathway of Ca2+ entry in cell function.     

Effects of ammonium ions on endplate channels

Miniature endplate currents, recorded from voltage-clamped toad sartorius muscle fibers in solutions containing ammonium ions substituted for sodium ions, were increased in amplitude and decayed exponentially with a slower time constant than in control (Na) solution. The peak conductance of miniature endplate currents was also greater in ammonium solutions. The acetylcholine null potential was - 2.8 +/- 0.8 mV in control solution, and shifted to 0.9 +/- 1.6 mV in solutions in which NH4Cl replaced half the NaCl. In solutions containing NH4Cl substituted for all the NaCl, the null potential was 6.5 +/- 1.3 mV. Single channel conductance and average channel lifetime were both increased in solutions containing ammonium ions. The exponential relationship between the time constant of decay of miniature endplate currents or channel lifetime and membrane potential was unchanged in ammonium solutions. A slight but consistent increase in peak conductance during miniature endplate currents and single channel conductance was seen as membrane potential became more positive (depolarized) in both control and ammonium solutions. Net charge transfer was greater in ammonium solutions than in control solution, whether measured during a miniature endplate current or through a single channel. The results presented here are consistent with an endplate channel model containing high field strength, neutral sites.     

NaCl对小麦根生长和无机离子分布的影响

培养在含NaCl营养液中的幼苗,根生长被抑制,线粒体超微结构受损伤。用扫描电镜、X-射线能谱仪和电感耦合等离子直读光谱（ICP）分析发现,培养在含NaCl营养液中的根,积累大量Na+和Cl-,而K+和Ca~（2+）的含量降低,无机离子总量和Na+/K+比值提高。     

Effect of pH, ionic strength and univalent inorganic ions on the reconstitution of aspartate aminotransferase

1. The effect of pH change on the reconstitution of aspartate aminotransferase (EC 2.6.1.1), i.e. the reactivation of the apoenzyme with coenzyme (pyridoxal phosphate and pyridoxamine phosphate), was studied in the pH range 4.2-8.9 by using three buffer systems at concentrations ranging from 0.025 to 0.1m. 2. Although the profile of the reconstitution rate-pH curve in the range pH5.2-6.8 (covered by sodium cacodylate-HCl buffer) reflects the influence of the H(+) concentration on the reconstitution process, the profile of the curve in the pH ranges 4.2-5.6 and 7.2-8.25 (covered respectively by sodium acetate-acetic acid and Tris-HCl buffers) appears to be influenced by the ionic strength of the buffer. 3. The reconstitution is also influenced by univalent inorganic ions such as halide ions and, to a lesser extent, alkali metal ions, which are known to alter the water structure.     

Effect of cupric ions on the permeability of erythrocyte membrane to non-electrolyte spin labels

The addition of cupric ions caused decreased permeability to hydrophilic molecules and increased permeability to hydrophobic molecules. These results suggest that TEMPOL penetrates the erythrocyte in a different way than TEMPO. Penetration of TEMPOL is controlled by-SH groups, while TEMPO probably diffuses through the lipid bilayer. Cupric ions increase the permeability of erythrocyte membranes to both non-electrolytes in vivo.     

Proteins,channels and crowded ions

Ion channels are proteins with a hole down their middle that control a vast range of biological function in health and disease. Selectivity is an important biological function determined by the open channel, which does not change conformation on the biological time scale. The challenge is to predict the function—the current of ions of different types and concentrations through a variety of channels—from structure, given fundamental physical laws. Walls of ion channels, like active sites of enzymes, often contain several fixed charges. Those fixed charges demand counter ions nearby, and the density of those counter ions is very high, greater than 5 molar, because of the tiny volumes of the channel's pore. Physical chemists can now calculate the free energy per mole of salt solutions (e.g. the activity coefficient) from infinite dilution to saturation, even in ionic melts. Such calculations of a model of the L-type calcium channel show that the large energies needed to crowd charges into the channel can account for the substantial selectivity and complex properties found experimentally. The properties of such crowded charge are likely to be an important determinant of the properties of proteins in general because channels are nearly enzymes.     

Effect of Escherichia coli heat-stable enterotoxin on cell volume and intracellular inorganic ions of rat intestinal cells

1.--Electron micrographs of rat jejunum mucosa incubated for 1 h in the presence of Escheria coli heat-stable enterotoxin (STa) in the lumen shows alterations of villous cells as well as of crypt cells. The brush border of mature enterocytes is partially desintegrated and covered with a thick mucus. Crypts are occupied on half of their height by cells very similar to Paneth cells, loaded with numerous large dark inclusions. 2.--Cell volume and intracellular inorganic ion concentrations have been estimated in mucosal scrapings of jejunum sacs, incubated in vitro for 1 or 3 h. The quick action (1 h of incubation) of STa is a swelling of the intestinal calls accompanied by an increase in Na+, Cl- and Ca2+ intracellular concentrations and a decrease in the K+ and Mg2+ ones. The delayed action (3 h of incubation) is an increase of extracellular space and a decrease in cell volume; and at the same time the intracellular concentration of Na+, Cl-, K+, Ca2+ and Mg2+ is augmented. 3.--After 3 h of incubation intestinal cells from the other levels of intestine (duodenum, ileum and colon) show the same variations in cell volume and intracellular inorganic ion concentrations under the influence of STa, as those recorded in the jejunum. 4.--The present work favours the hypothesis that all intestinal cells, villous or cryptic, are involved in the alteration of fluid ion transport ending in diarrhea.