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PubMed1980

Effects of divalent cations on calcium levels, aggregation and morphology of human blood platelets in vitro.

Some effects of cadmium, nickel, strontium and manganese ions upon human platelets in vitro are reported. Both Mn and Cd induced aggregation, Mn being the most effective. Ni and Sr did not have this effect. Scanning electron microscopic observation showed that Mn and Cd, but not Ni and Sr induced shape changes in the platelets. X-ray microanalysis of pyroantimonate fixed platelets revealed that calcium was displaced from both membrane and cytoplasmic regions by all four cations. The magnitude of displacement occurred in the sequence Mn > Cd > Ni approximately or equal to Sr. Manganese was detected both in the cytoplasm and membrane region of those platelets treated with this ion. It is suggested that the cations are influencing directly certain macromolecular ligands whose condition controls platelet surface properties.

Blood Platelets↗
PubMed1994

[The effect of divalent cations on the kinetics of the activation and blockade of the nicotinic cholinoreceptor ion channel in rat skeletal muscle].

The influence of alkaline earth metal ions calcium and magnesium on the conductance and on the kinetics of activation and atropine-induced blockade of nicotinic cholinoreceptor ion channels in cultured rat skeletal muscle were studied using patch-clamp technique. In physiological concentrations these cations influence both conductance and kinetics of blockade, but have no significant effect on the kinetics parameters of activation. The data suggest that physiological cations modulate the generation of postsynaptic potentials in the normal condition as well as in the presence of blocking drugs.

Acetylcholine↗
PubMed1995

Serum and urinary divalent cations and plasma renin activity in women with mild pregnancy-induced hypertension.

Serum concentrations and urinary output of calcium, magnesium, sodium and potassium were analysed in normotensive pregnant women and in women with pregnancy-induced hypertension during the third trimester. In addition, plasma renin activity (PRA) was also determined. Significantly lower serum total calcium, urinary calcium and magnesium excretions and plasma renin activity were evident in women with PIH. Urine output and creatinine clearance were not significantly different between the two groups. No significant correlation was evident between serum calcium, magnesium and PRA. The relationship between these parameters and high blood pressure is not immediately apparent. They nevertheless suggest of a disturbance in electrolyte metabolism in women with PIH, that may underly the pathogenesis of this disorder.

Adult↗
PubMed1994

[The role of disorders in the homeostasis of divalent cations in the pathogenesis and clinical picture of bronchial asthma].

Mg and Ca concentrations in the serum, red cells, lymphocytes and 24-h urine were examined in 13 preasthma (PA) patients, 26 atopic asthma patients and 23 bacterial asthma (BA) patients. The patients' age ranged from 15 to 65 years. The measurements were made on AAC-508 absorption spectrophotometer (Hitachi, Japan) and Microlyte selective ionometer (Kone, Finland). Lack of Mg and excess of Ca in blood cells and low Mg values in circadian urine were recorded in all the patients irrespective of the disease variant, phase, course, broncho-obstruction. Changes in cell electrolyte composition in asthma and PA patients seem to disturb cAMP metabolism and to enhance lipid peroxidation, thus being responsible for bronchial hyperreactivity. Superactivation of free-radical lipid peroxidation in cellular membranes is suggested to underlie, among other factors, defective intracellular homeostasis of bivalent cations in the above patients.

Adolescent↗
PubMed1978

[Permeability of the isolated human amniotic membrane to divalent cations].

Membrane potential and resistance recordings, in vitro, show that Mg++ does not pass through the amnion from the inside of the amniotic compartment to the outside of the amniotic membrane. Mg++ may become fixed on the surface or in the midst of the amniotic membrane. However, Mg++ diffuses in the opposite direction. Ca++, Ba++, Sr++ diffuse in both directions across the amniotic membrane.

Amnion↗
PubMed1978

Divalent cation mobility throughout exponential growth and sporulation of Bacillus megaterium.

Each of the five elements considered was taken up by Bacillus megaterium during exponential growth. Initial Mg and Mn uptake was rapid and ended by mid-log. For Ca, Fe, and Zn, uptake continued throughout exponential growth. Elements were released from the cells immediately following initial uptake. For Mn, egression continued to t2, with release of 36% of total accumulated. Secondary uptake followed immediately and continued through stage V. Magnesium egression continued to t1 with release of 33% accumulated. Secondary uptake began by t5 (stage IV) and continued slowly through sporulation. Calcium egression ceased by t4 with release of 25% total accumulated. Secondary uptake began by t6 (stage V) and continued until depleted. Zinc egression stopped by t5 with release of 34% accumulated with some secondary uptake by stage V. Iron egression terminated at t4 with release of 59% of total accumulated. This was followed by secondary uptake after t12 (stage VI).

Bacillus megaterium↗
PubMed2002

In vitro fusion of plant Golgi membranes can be influenced by divalent cations.

The fusogenic activity of plant Golgi membranes was studied in a cell-free system by assaying lipid mixing and content leakages of fluorescence probes. Golgi membranes from mung bean (Vigna radiata L.) hypocotyl cells fused to liposomes in the absence of any cytosolic proteins and nucleotides. It was demonstrated that the fusion was mediated by integral membrane protein(s), and was influenced by divalent cations (mm). Mg(2+), Ca(2+), and Mn(2+) ions enhanced the lipid mixing by reducing repulsive forces between membranes. In the content leakage assay, Mg(2+) ions also showed a stimulative effect. However, other divalent cations were inhibitory. It is suggested that the fusion system of Golgi membranes comprises at least two components: one that mediates the formation of fusion intermediates prior to pore opening, and one that mediates the subsequent processes. The latter must be sensitive to divalent cations at millimolar concentrations. The fusion of Golgi and biological membranes was induced by divalent cations. We speculated about the biological role of the fusion system studied here.

Calcium↗
PubMed1983

Evidence for a divalent cation dependent catecholamine storage complex in chromaffin granules.

Chromaffin granules, the secretory vesicles of the adrenal medulla, are stable in isotonic sucrose solutions at room temperature; however, when low concentrations of the ionophore A23187 are added, rapid lysis ensues which is dependent on the presence of a divalent cation chelator and is prevented by the addition of either Ca2+ or Mg2+. As little as 10 microM Ca2+ totally inhibit lysis of chromaffin granules by A23187, while 28 mM KCl have no effect. Lysis by A23187 at 4.7 microM is almost 100% in the presence of EDTA in isotonic sucrose in 1 h and can be suppressed by raising the osmotic strength of the medium with half maximal inhibition at 0.57 M sucrose, demonstrating that A23187 causes osmotic lysis of chromaffin granules as a consequence of the withdrawal of divalent cations from the core solution. Our results strongly suggest that divalent cations are involved in the formation of a ionic complex in the core solution which lowers its effective osmotic pressure.

Animals↗
PubMed2003

The ATPase activity of GroEL is supported at high temperatures by divalent cations that stabilize its structure.

Previously, we reported that the ATPase activity of GroEL that requires potassium and magnesium was highly temperature dependent in the 25-60 degrees C range. Here, we report that the monovalent cations, rubidium and ammonium were able to fully substitute for potassium; while the divalent cations manganese, cobalt, and nickel supported the ATPase activity of GroEL albeit to a lesser degree than magnesium. ATPase activities with manganese, cobalt, and nickel were 64%, 41%, and 29%, respectively, of the maximum activity (100%) when utilizing magnesium. Interestingly, the ability of all the cations to support the GroEL ATPase activity was somewhat consistent over the entire 25-60 degrees C range. Maximum ATPase activities were observed at 49 degrees C. Here, the influence of these cations on the thermal denaturation of GroEL was also monitored using bisANS binding as an indication of the exposure of hydrophobic surfaces during thermal denaturation of GroEL. Maximum exposure of hydrophobic surfaces on GroEL alone or in the presence of each of the monovalent cations was determined to occur at 65 degrees C. However, the maximum exposure of hydrophobic surfaces on GroEL in the presence of magnesium, manganese, cobalt or nickel was found to occur at 71 degrees C indicating that GroEL is significantly stabilized against thermal denaturation by these divalent cations.

Adenosine Triphosphatases↗
PubMed1996

The role of the divalent cation in the structure of the I domain from the CD11a/CD18 integrin.

BACKGROUND: The integrin family of cell-surface receptors mediates a wide variety of cell-cell and cell-extracellular matrix interactions. Integrin-ligand interactions are invariably dependent on the presence of divalent cations, and a subset of integrins contain a approximately 200 amino acid inserted (I) domain that is important for ligand binding activity and contains a single divalent cation binding site. Many integrins are believed to respond to stimuli by undergoing a conformational change that increases their affinity for ligand, and there is a clear difference between two crystal structures of the CD11b I domain with different divalent cations (magnesium and manganese) bound. In addition to the different bound cation, a 'ligand mimetic' crystal lattice interaction in the CD11b I domain structure with bound magnesium has led to the interpretation that the different CD11b I domain structures represent different affinity states of I domains. The influence of the bound cation on I domain structure and function remains incompletely understood, however. The crystal structure of the CD11a I domain bound to manganese is known. We therefore set out to determine whether this structure changes when the metal ion is altered or removed. RESULTS: We report here the crystal structures of the CD11a I domain determined in the absence of bound metal ion and with bound magnesium ion. No major structural rearrangements are observed in the metal-binding site of the CD11a I domain in the absence or presence of bound manganese ion. The structures of the CD11a I domain with magnesium or manganese bound are extremely similar. CONCLUSIONS: The conformation of the CD11a I domain is not altered by changes in metal ion binding. The cation-dependence of ligand binding thus indicates that the metal ion is either involved in direct interaction with ligand or required to promote a favorable quaternary arrangement of the integrin.

Amino Acid Sequence↗
PubMed1986

High affinity binding of divalent cation to actin monomer is much stronger than previously reported.

Monomeric actin is known to bind tightly one divalent cation per molecule. We have quantitatively reinvestigated the affinity of actin for Ca++ and Mg++ using the fluorescent Ca++ chelator Quin2 to induce and measure the dissociation of Ca++ from Ca-actin, supporting these studies with measurements using 45Ca. We found that the KD for Ca-actin is actually 1.9 +/- 0.7 nM. Kinetic analysis supported this result and demonstrated a dissociation rate constant (k-) of 0.013 s-1 and an association rate constant (k+) of 6.8 X 10(6)M-1 s-1 for Ca-actin. Competitive binding studies indicated that the binding affinity of actin for Ca++ is 5.4 times that for Mg++, yielding a calculated KD for Mg-actin of about 10 nM. Thus, the tight-binding of divalent cations to actin is 3-4 orders of magnitude stronger than previously thought.

Actins↗
PubMed2002

Divalent cations and polyamines bind to loop 8 of 14-3-3 proteins, modulating their interaction with phosphorylated nitrate reductase.

Binding of 14-3-3 proteins to nitrate reductase phosphorylated on Ser543 (phospho-NR) inhibits activity and is responsible for the inactivation of nitrate reduction that occurs in darkened leaves. The 14-3-3-dependent inactivation of phospho-NR is known to require millimolar concentrations of a divalent cation such as Mg2+ at pH 7.5. We now report that micromolar concentrations of the polyamines, spermidine(4+) and spermine(3+), can substitute for divalent cations in modulating 14-3-3 action. Effectiveness of the polyamines decreased with a decrease of polycation charge: spermine(4+) > spermidine(3+) >>> cadavarine(2+) approximately putrescine(2+) approximately agmatine(2+) approximately N1-acetylspermidine(2+), indicating that two primary and at least one secondary amine group were required. C-terminal truncations of GF14 omega, which encodes the Arabidopsis 14-3-3 isoform omega, indicated that loop 8 (residues 208-219) is the likely cation-binding site. Directed mutagenesis of loop 8, which contains the EF hand-like region identified in earlier studies, was performed to test the role of specific amino acid residues in cation binding. The E208A mutant resulted in a largely divalent cation-independent inhibition of phospho-NR activity, whereas the D219A mutant was fully Mg(2+)-dependent but had decreased affinity for the cation. Mutations and C-terminal truncations that affected the Mg(2+) dependence of phospho-NR inactivation had similar effects on polyamine dependence. The results implicate loop 8 as the site of divalent cation and polyamine binding, and suggest that activation of 14-3-3s occurs, at least in part, by neutralization of negative charges associated with acidic residues in the loop. We propose that binding of polyamines to 14-3-3s could be involved in their regulation of plant growth and development.

14-3-3 Proteins↗
PubMed1999

Redox reagents and divalent cations alter the kinetics of cystic fibrosis transmembrane conductance regulator channel gating.

Gating of the cystic fibrosis Cl(-) channel requires hydrolysis of ATP by its nucleotide binding folds, but how this process controls the kinetics of channel gating is poorly understood. In the present work we show that the kinetics of channel gating and presumably the rate of ATP hydrolysis depends on the species of divalent cation present and the oxidation state of the protein. With Ca(2+) as the dominant divalent cation instead of Mg(2+), the open burst duration of the channel is increased approximately 20-fold, and this change is reversible upon washout of Ca(2+). In contrast, "soft" divalent cations such as Cd(2+) interact covalently with cystic fibrosis transmembrane conductance regulator (CFTR). These metals decrease both opening and closing rates of the channel, and the effects are not reversed by washout. Oxidation of CFTR channels with a variety of oxidants resulted in a similar slowing of channel gating. In contrast, reducing agents had the opposite effect, increasing both opening and closing rates of the channel. In cell-attached patches, CFTR channels exhibit both oxidized and reduced types of gating, raising the possibility that regulation of the redox state of the channel may be a physiological mode of control of CFTR channel activity.

Adenosine Triphosphate↗