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PubMed1993

A negative charge in the M2 transmembrane segment of the neuronal alpha 7 acetylcholine receptor increases permeability to divalent cations.

Threonine-244 (T244) in the putative channel-forming M2 segment of the neuronal alpha 7 acetylcholine receptor (AChR), a residue proposed to form part of the selectivity filter, was mutated to aspartic acid to examine the influence of a negative charge on AChR ion permeation properties. Wild type (AChR alpha 7wt) and mutant (AChR alpha 7D244) acetylcholine receptors expressed in Xenopus oocytes give rise to acetylcholine (ACh)-activated, alpha-bungarotoxin-sensitive, cation-selective ionic currents. AChR alpha 7D244 exhibited larger currents than AChR alpha 7wt that, in addition, activated at lower ACh concentrations. The relative ionic permeability (Px/PNa) of AChR alpha 7wt to K+ was PK/PNa = 1.2, and to Ba2+, P'Ba/PNa = 1.4. In contrast, AChR alpha 7D244 was less selective in discriminating between K+ and Na+, PK/PNa = 0.95, but exhibited a remarkable increase in permeability to Ba2+, P'Ba/PNa = 3.7. Furthermore, only mutant receptors were permeable to Mg2+. Hence, a ring of negatively charged residues in the putative pore-forming segment of the receptor increases the permeability to divalent cations. Our results substantiate the notion that T244, or its equivalent, in the M2 transmembrane segment of cholinergic receptor channels is a key structural determinant of the selectivity filter.

Acetylcholine↗
PubMed1991

Adherence-induced enhancement of the oxidative burst of human neutrophilic granulocytes: effects of the surface coat and of divalent cations.

Neutrophilic granulocytes are capable of adhering to biological or artificial surfaces. In addition to specific interactions between adherence molecules on the cell surface and corresponding structures on other cells or matrix proteins like fibronection or collagen there appeared to be non-specific attachment as well. Adherence augmentation induced by stimulation with chemotactic factors or cytokines was an active process which did not proceed at 4 degrees C and after removal of divalent cations from the medium. Adherence acted as a priming stimulus increasing the amount of superoxide anion and hydrogen peroxide produced in response to stimulation by certain chemotactic factors and cytokines. Adherence priming like priming by GM-CSF was strongly suppressed by chelation of intracellular Ca2+ ions. The two priming mechanisms differed, however, in their requirement for divalent cations in the external medium: whereas Mg2+ suppressed GM-CSF priming, it synergised with Ca2+ in the adherence-augmented oxidative burst.

Calcium↗
PubMed1994

Divalent cations in hypertension with implications to heart disease: calcium, cadmium interactions.

Heart disease still pervades all socioeconomic classes within the United States. Understanding the effects of environmentally-related pathogenesis (e.g., heavy metal accumulation) may aid in developing novel treatments for the prevention of heart dysfunction. The aim of this report was to use experimental investigation in an attempt to expand upon the multivariate importance of divalent cation interactions in the development of heart disease. Calcium and cadmium levels were measured by flame atomic absorption spectrophotometry in various tissues derived from two types of hypertensive rabbit models. Both models of hypertension developed mean arterial pressures of at least 50 mm mercury greater than those of controls over a 5 week period. Interrelationships between calcium and cadmium levels were found to exist for both hypertensive groups in the left ventricle, aorta, and renal medulla. The renal cortex showed no such interrelationship for the renal hypertensive group. Multiple interrelationships between calcium and cadmium levels and hypertrophy were also observed. These studies related the importance of endogenous or exogenous (viz, environmental) factors governing cadmium and calcium accumulation in hypertensive rabbits. The resulting relationships between divalent cations and hypertrophy were presented to draw attention to areas which remain unexplored with perspective to cardiovascular disease.

Animals↗
PubMed1976

Inhibition of dihydrostreptomycin binding to Mycobacterium smegmatis by monovalent and divalent cation salts.

To better understand salt antagonism of dihydrostreptomycin (DSM) action on Mycobacterium smegmatis, the effects of monovalent and divalent cation salts on drug uptake were studied in relation to the lethal activity of DSM. In Sauton liquid medium NaCl, MgCl(2), and SrCl(2) inhibited the initial instantaneous binding of [(3)H]DSM to the organism and suppressed secondary uptake. These data correlated well with the capacity of each salt to prevent the lethal activity of DSM. It was concluded that monovalent and divalent cation salt antagonism of DSM action on M. smegmatis involves nonspecific interference with drug uptake.

Chlorides↗
PubMed1993

Divalent cation binding to erythrocyte spectrin.

Erythrocyte spectrin dimers and separated alpha- and beta-spectrin chains bound 45Ca2+ after electrophoresis on native or sodium dodecyl sulfate-polyacrylamide gels, blotting, and 45Ca2+ overlay. Flow dialysis and equilibrium dialysis revealed two binding components: high-affinity, Ca(2+)-specific sites with kd = 4 x 10(-7) M and n = 100 +/- 20 per dimer and a low-affinity (millimolar) divalent cation component. Whereas brain spectrin had only four high-affinity sites [Wallis, C. J., Wenegieme, E. F., & Babitch, J. A. (1992) J. Biol. Chem. 267, 4333-4337], erythrocyte spectrin had 25-fold more sites per dimer. In addition to possibly modifying spectrin interactions with calcium-dependent protease and actin, as suggested by previous work on the interaction of Ca2+ with brain spectrin, the approximately two high-affinity sites per repeating segment of erythrocyte spectrin appear to stabilize a folded conformation of repeat structures indicated by an entropy increase upon binding. These data support the hypothesis that divalent cation binding to erythrocyte spectrin has become specialized to stabilize the membrane skeletal network and the cell, making them flexible but resistant to shear under the stressful conditions of blood circulation.

Animals↗
PubMed1993

Divalent cations selectively alter the voltage dependence of inactivation of A-currents in chick autonomic neurons.

A-currents were studied in acutely dissociated chick autonomic neurons. Switching from salines containing 4 mM Mg2+ to salines containing 4 mM Ca2+ caused a large positive shift in the voltage dependence of steady-state inactivation, but had no effect on the voltage dependence or kinetics of activation, deactivation, the rate at which channels became inactivated, or the rate at which channels recovered from inactivation. This effect saturated with increasing concentrations of Ca2+. Other group IIA divalent cations were less effective than Ca2+, in the order Ca2+ > Ba2+ > Mg2+ = Sr2+. Application of 4 mM Mg2+ partially antagonized the effects of 4 mM Ca2+. The results suggest that divalent cations selectively alter the voltage dependence of steady-state inactivation by acting at sites accessible from the outside of the cell.

Animals↗
PubMed1990

Divalent cation activation of galactosyltransferase in native mammary Golgi vesicles.

Millimolar concentrations of manganese are required for maximal activation of purified galactosyltransferase (lactose synthase, EC 2.4.1.22), the enzyme that catalyzes addition of galactosyl groups to proteins and, in lactose synthesis, to glucose. To examine manganese activation of this enzyme under in vivo conditions, we studied intact, partially purified Golgi membranes from mouse mammary glands. In intact vesicles treated with the divalent cation ionophore, A23187, activation followed Michaelis-Menton kinetics with a Km of 3 microM; maximal activation was achieved below 10 microM manganese. In both detergent-solubilized and leaky vesicles the kinetics of manganese activation were consistent with the presence of two manganese-binding sites with dissociation constants about 40 microM and 20 mM. The difference is consistent with the presence in intact vesicles of an endogenous activator too large to traverse the membrane via A23187; this activator could bind to the low affinity manganese site allowing manganese or another divalent cation such as zinc to activate the enzyme at micromolar concentrations. The Km for UDP-galactose was found to be similar in the vesicular and solubilized preparations at micromolar and millimolar manganese concentrations, respectively, providing additional evidence for this hypothesis.

Animals↗
PubMed1987

Control of membrane permeability in animal cells by divalent cations.

The permeability of several cell lines, including HeLa, L929, 3T6 and 3T3, to various compounds is affected by the concentration of divalent cations in the culture medium. In the absence of Mg2+ ions but with 4-8 mM CaCl2 in the medium, HeLa and L929 cells become permeabilized, as measured by the entry of the aminoglycoside antibiotic hygromycin B. However, 3T3 and 3T6 cells become much more permeable when calcium and magnesium are both absent from the medium. Addition of Mg2+ above 2 mM abolishes the permeabilization induced by Ca2+. Basic pH favors permeabilization, whereas acidic pH inhibits the entry of hygromycin B. Increased entry of macromolecules, such as the toxin alpha-sarcin, horseradish peroxidase (HRP) and luciferase, is also observed under permeabilization conditions, suggesting that this method could be of general use, since it is not harmful to cells and is fully reversible. Exit of 86Rb+ ions and [3H]uridine-labelled nucleotides was also assayed. We did not observe increased release of these compounds from preloaded cells under various calcium concentrations. Finally, the effects of several inhibitors of endocytosis and other membrane functions on the permeabilization inhibitors of endocytosis and other membrane functions on the permeabilization process were also analysed. The entry of alpha-sarcin was not affected by nifedipine, dibucaine or mepacrine, but was partially inhibited by NH4Cl, amantadine and chloroquine.

Animals↗
PubMed1980

Differential effects of divalent cations, cation chelators and an ionophore (A23187) on morphine and dibutyryl guanosine 3': 5'-cyclic monophosphate antinociception.

The effects of intraventricularly (i.c.v.) administered divalent cations, cation chelators and an ionophore (A23187) on antinociception produced by i.c.v. administration of morphine or dibutyryl guanosine 3':5'-cyclic monophosphate (db c-GMP) were quantitated in the mouse tail-flick procedure. Ca++ pretreatment produced a dose-related potentiation (> 10-fold) of db c-GMP and a dose-related antagonism (> 20-fold) of morphine antinociception. Mg++ pretreatment antagonized db c-GMP, whereas morphine antinociception was unaffected. Ba++ and Sr++ were observed to possess intrinsic antinociceptive activity. Administration of Ba++ or Sr++ had greater than additive effects on db c-GMP and morphine antinociception. EDTA pretreatment did not affect db c-GMP or morphine antinociception. Ethylene glycol bis(beta-aminoethyl ether)N,N-tetraacetic acid had no effect on db c-GMP but potentiated the morphine response. The ionophore A23187 had no effect on db c-GMP or morphine in the tail-flick test. However, A23187 potentiated the effect of high doses of Ca++ on db c-GMP and increased the antagonistic effect of a low dose of Ca++ on morphine antinociception. The results provide further evidence that the mechanism of db c-GMP antinociception is different from that of morphine.

Analgesics↗
PubMed2004

Dynamic change in the distribution of alpha5beta1 integrin on isolated ventral membrane: effect of divalent cation species.

We investigated the spatial distribution of alpha5beta1 integrin in isolated ventral plasma membranes (VPMs) of human foreskin fibroblasts in order to elucidate how the interaction of integrin with cytoskeletal and extracellular matrix proteins might affect the integrin distribution. Cells were exposed to the jet of buffer to remove the apical surface and most of cellular organelles. After this treatment VPMs, which adhered to the glass surface, possessed the cellular structures such as fibronectin (FN) fibrils and actin stress fibers. The isolated VPMs thus prepared were employed without fixation to investigate the change in the integrin distribution. In isolated VPMs, alpha5beta1 integrin, labeled with Cy3-tagged anti-integrin antibody, was found to accumulate not only at the tips of stress fibers but also along FN fibrils extending from there. When divalent cations were removed with EDTA, the accumulated integrin was dispersed, and the original pattern of distribution was recovered upon restoration of divalent cations. Talin, an integrin-actin cytoskeleton linker protein, was found to accumulate only at the tips of stress fibers in isolated VPMs, but alpha5beta1 integrin did not exhibit strong accumulation there, indicating that talin played little role in integrin distribution in isolated VPMs. The amount of alpha-actinin associated with stress fibers was found to drastically decrease in isolated VPMs, which was presumably related to the failure of localization of integrin at the tips of stress fibers. It was also shown that the association of stress fibers to isolated VPMs seemed to be independent of accumulation of integrin.

Actinin↗
PubMed2001

Molecular cloning of a putative divalent-cation transporter gene as a new genetic marker for the identification of Lactobacillus brevis strains capable of growing in beer.

Random amplified polymorphic DNA (RAPD) PCR analysis of Lactobacillus brevis isolates from breweries revealed that one of the random primers could distinguish beer-spoilage strains of L. brevis from nonspoilage strains. The 1.1-kb DNA fragment amplified from all beer-spoilers included one open reading frame, termed hitA (hop-inducible cation transporter), which encodes an integral membrane protein with 11 putative trans-membrane domains and a binding protein-dependent transport signature of a non-ATP binding membrane transporter common to several prokaryotic and eukaryotic transporters. The hitA polypeptide is homologous to the natural resistance-associated macrophage protein (Nramp) family characterized as divalent-cation transport proteins in many prokaryotic and eukaryotic organisms. Northern blot analysis indicated that the hitA transcripts are expressed in cells cultivated in MRS broth supplemented with hop bitter compounds, which act as mobile-carrier ionophores, dissipating the trans-membrane pH gradient in bacteria sensitive to the hop bitter compounds by exchanging H+ for cellular divalent cations such as Mn2+. This suggests that the hitA gene products may play an important role in making the bacteria resistant to hop bitter compounds in beer by transporting metal ions such as Mn2+ into cells that no longer maintain the proton gradient.

Amino Acid Sequence↗
PubMed1976

Divalent cation affinity sites in Paramecium aurelia.

Sites with high calcium affinity in Paramecium aurelia were identified by high calcium (5 mM) fixation and electron microscope methods. Electron-opaque deposits were observed on the cytoplasmic side of surface membranes, particularly at the basal regions of cilia and trichocyst-pellicle fusion sites. Deposits were also observed on some smooth cytomembranes, within the axoneme of cilia, and on basal bodies. The divalent cations, Mg2+, Mn2+, Sr2+, Ni2+, Ba2+, and Zn2+, could be substituted for Ca2+ in the procedure. Deposits were larger with 5 mM Sr2+. Ba2+, and Mn2+ at ciliary transverse plates and the terminal plate of basal bodies. Microprobe analysis showed that Ca and C1 were concentrated within deposits. In some analyses, S and P were detected in deposits. Also, microprobe analysis of 5 mM Mn2+-fixed P. aurelia showed that those deposits were enriched in Mn and C1 and sometimes enriched in P. Deposits were seen only when the ciliates were actively swimming at the time of fixation. Locomotory mutants having defective membrane Ca-gating mechanisms and ciliates fixed while exhibiting ciliary reversal showed no obvious differences in deposition pattern and intensity. Possible correlations between electron-opaque deposits and the locations of intramembranous particles seen by freeze-fracture studied, as well as sites where fibrillar material associate with membranes are considered. The possibility that the action sites of calcium and other divalent cations were identified is discussed.

Animals↗
PubMedDate not supplied

[Study of structural changes in chromatin in the presence of mono- and divalent cations by means of flow linear dichroism].

The chromatin structure in solution was studied by the flow linear dichroism method (LD) in a wide range of ionic strengths. It was found that the increasing of the ionic strength from 0.25 mM EDTA, pH 7.0 to 100 mM NaCl leads to a manifold decrease of the LD amplitude of chromatin and inversion of the LD sign from negative to positive at 2 mM NaCl. Chromatin exhibits a positive LD maximum value at 10-20 mM NaCl. These data enable us to conclude that in very low ionic strength (0.25 mM EDTA-2mM NaCl) the nucleosome discs are oriented with their flat faces parallel to the chromatin filament axis. Increasing ionic strength up to 20 mM NaCl leads to reorientation of the nucleosome discs and to formation of chromatin structure with nucleosome flat faces more or less perpendicular to the fibril axis. A conformational transition of that kind is not revealed in H1-depleted chromatin. This testifies to the fact that the histone H1 is responsible for the higher order structure of chromatin. It was found that divalent cations do not induce the inversion of the LD sign of chromatin.

Animals↗
PubMed2006

Augmentation of microsporidia adherence and host cell infection by divalent cations.

The infection process of intracellular opportunistic microsporidia involves the forcible eversion of a coiled hollow polar filament that pierces the host cell membrane, allowing the passage of infectious sporoplasm into the host cell cytoplasm. Although the exact mechanism of spore activation leading to polar filament discharge is unknown, we have shown that spore adherence to host cells, which is mediated by sulfated glycosaminoglycans, may play a vital role. When adherence is inhibited, host cell infection decreases, indicating a direct link between adherence and infection. The goal of this study was to evaluate the effects of exogenous divalent cations on microsporidia spore adherence and infection. Data generated using an in vitro spore adherence assay show that spore adherence is augmented by manganese (Mn2+) and magnesium (Mg2+), but not by calcium (Ca2+). However, each of the three divalent cations contributed to increased host cell infection when included in the assay. Finally, we show that Mn2+ and Mg2+ may activate a constituent on the microsporidia spore, not on the host cell, leading to higher infection efficiency. This report further supports recent evidence that spore adherence to the host cell surface is an important aspect of the microsporidial infection process.

Animals↗
PubMedDate not supplied

[Quantitative determination of bacterial endotoxins by the chromogenic limulus method: critical analysis and study of interactions between 3 divalent cations].

The reproducibility of the limulus amoebocyte lysate (LAL) test with the use of a chromogenic substrate was evaluated in the presence of 5 bacterial endotoxins (2 from Escherichia coli, 1 from Salmonella, 1 from Serratia marcescens and 1 from Vibrio cholerae) and the FDA reference endotoxin EC5. Endotoxins from E. coli 055B5, S. marcescens and V. cholerae were significantly more active than the reference endotoxin (p less than 0.01). Addition of Mg2+ activated the LAL chromogenic reaction (optimum = 160 mmol/l added), whereas Ca2+ in concentrations above 5 mmol/l inhibited the reaction. As little as 0.3 mmol/l Zn2+ strongly inhibited the reaction. Inhibition by Zn2+ was partly suppressed by addition of 160 mmol/l Mg2+. These divalent cations modified the LAL chromogenic reaction when added in the first step of the reaction (incubation with endotoxin and LAL reagent). The LAL chromogenic reaction was not modified by divalent cations when these were added in the second step of the reaction (with the chromogenic substrate).

Animals↗
PubMed2006

Transmission of viruses to mosquito larvae mediated by divalent cations.

The two major groups of pathogenic viruses in mosquitoes are the occluded viruses, represented by baculoviruses and cypoviruses, and the non-occluded viruses, represented by the densoviruses and the iridoviruses. Baculoviruses, densoviruses, and iridoviruses are DNA viruses, while cypoviruses are the major group of RNA viruses reported from mosquitoes. Research on mosquito pathogenic viruses has been limited, in part, due to the inability to effectively transmit them to the larval mosquito host. Recently, there have been tremendous advancements in the ability to transmit mosquito baculoviruses and cypoviruses with the finding that transmission is mediated by divalent cations. Oral transmission of both baculoviruses and cypoviruses to mosquito larvae is enhanced by magnesium and inhibited by calcium ions. The current status of transmission for each of the major groups is reviewed with emphasis on the common role of divalent cations in transmission of the distantly related baculoviruses and cypoviruses.

Animals↗
PubMed1981

Metal ion content of dolichos biflorus lectin and effect of divalent cations on lectin activity.

The metal ion content of the Dolichos biflorus seed lectin has been determined by using atomic absorption spectrophotometry. Ca2+, Mg2+, Mn2+, Zn2+, and Cu2+ were all found in the native lectin and could be removed to different degrees by using a variety of techniques such as high ionic strength, low pH, chelating agent, and combinations of these procedures. By use of affinity electrophoresis, the remaining binding capacity of the lectin could easily be determined, and the D. biflorus lectin showed an absolute requirement for divalent cations to be able to bind N-acetyl-D-galactosamine. The association constant (Ka) of the lectin for N-acetyl-D-galactosamine was determined after remetallization of the lectin with each individual metal ion and a combination of them. The Ka of the lectin for the hapten differed depending on which divalent cation had been used for remetallization. Ca2+ ion alone was equal to a combination of all metal ions in its ability to confer the highest binding activity of the lectin for N-acetyl-D-galactosamine. The other cations, Mg2+, Mn2+, Zn2+, and Cu2+, could not restore the binding activity of the lectin to the same degree as Ca2+ or a combination of all ions. The D. biflorus lectin is, therefore, one of the first lectins that has been shown to require only a single cation to fully retain its binding activity in contrast to most lectins that require a combination of Ca2+, Mn2+, Mg2+, or Zn2+. Furthermore, we have shown that there is a selective process of ion uptake into the lectin since the metal ion ratios in the native lectin compared to the whole seed are quite different.

Cations, Divalent↗
PubMed1989

Evidence for divalent cation (Ca2+)-stabilized oligomeric proteins and covalently bound protein-peptidoglycan complexes in the outer membrane of Rhizobium leguminosarum.

Two unusual characteristics of some outer membrane proteins of Rhizobium leguminosarum are described. First, most of the major outer membrane proteins could only be visualized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis after lysozyme treatment of the isolated cell envelopes, suggesting a very strong, possibly covalent, interaction of these proteins with the peptidoglycan. These peptidoglycan-associated outer membrane proteins belonged to two distinct groups of immunologically related proteins, groups II and III, as defined by typing with monoclonal antibodies. As members of both groups of proteins could be radioactively labeled by growing cells in the presence of N-[3H]acetylglucosamine, we propose that variation in the apparent molecular weight of the antigens within each group is caused by varying numbers of peptidoglycan subunit residues on only two or three different outer membrane proteins. Second, group III outer membrane proteins, with masses of 35 to 46 kilodaltons, formed oligomers stabilized by divalent cations which resisted complete denaturation in 2% sodium dodecyl sulfate at 100 degrees C. Reconstitution experiments showed that of the divalent cations tested, Ca2+ and, to a lesser extent, Mn2+ and Sr2+ were the best stabilizers.

Acetylglucosamine↗