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PubMed1992

Tightly-bound divalent cation of actin.

Actin is known to undergo reversible monomer-polymer transitions that coincide with various cell activities such as cell shape changes, locomotion, endocytosis and exocytosis. This dynamic state of actin filament self-assembly and disassembly is thought to be regulated by the properties of the monomeric actin molecule and in vivo by the influence of actin-associated proteins. Of major importance to the properties of the monomeric actin molecule are the presence of one tightly-bound ATP and one tightly-bound divalent cation per molecule. In vivo the divalent cation is thought to be Mg2+ (Mg-actin) but in vitro standard purification procedures result in the preparation of Ca-actin. The affinity of actin for a divalent cation at the tight binding site is in the nanomolar range, much higher than earlier thought. The binding kinetics of Mg2+ and Ca2+ at the high affinity site on actin are considered in terms of a simple competitive binding mechanism. This model adequately describes the published observations regarding divalent cation exchange on actin. The effects of the tightly-bound cation, Mg2+ or Ca2+, on nucleotide binding and exchange on actin, actin ATP hydrolysis activity and nucleation and polymerization of actin are discussed. From the characteristics that are reviewed, it is apparent that the nature of the bound divalent cation has a significant effect on the properties of actin.

Actins↗

PubMed1990

Modulation of Na+/alanine cotransport in liver sinusoidal membrane vesicles by internal divalent cations.

Rat liver basolateral plasma membrane (blLPM) vesicles resuspended in 5 mM Mg2(+)-, Ca2(+)-, Mn2(+)- or Co2(+)-containing media exhibited a markedly lower rate of Na(+)-stimulated L-alanine transport. Divalent cation inhibition of L-alanine uptake was dose dependent, and was observed only when the vesicles were pre-loaded with the divalent cations. The presence or absence of the metal ions in the extravesicular incubation media had no effect on L-alanine transport. Conversely, pretreatment of the vesicles with 0.2 mM of either EGTA or EDTA resulted in higher initial rates of L-alanine transport. This stimulation was overcome by addition of excess divalent cation to the vesicle suspension solution. Since these blLPM vesicles are primarily oriented right-side-out, the divalent cation inhibition of L-alanine transport appears to be a result of their interaction with cytosolic components of the cell membrane. Total Na+ flux as measured with 22Na+ was not affected by intravesicular 5 mM Mg2+ or Ca2+, indicating that the inhibition was not due to dissipation of the Na+ gradient. These observations suggest that intracellular divalent cations may serve to modulate L-alanine transport across the liver cell plasma membrane.

Alanine↗

PubMed2001

Structural transition of d(G4T4G4) from antiparallel to parallel G-quartet induced by divalent cations.

We obtained thermodynamic parameters of an antiparallel G-quartet formation of d(G4T4G4) with 1 mM divalent cation (Mg2+, Ca2+, Mn2+, Co2+, or Zn2+). In addition, we also found that a higher concentration of a divalent cation induced a transition from an antiparallel to a parallel G-quartet structure. These results indicate that the divalent cations are a good tool for regulating the G-quartet structures and their stability.

Base Sequence↗

PubMed1991

Inhibition by EDTA and enhancement by divalent cations or polyamines of the dithiothreitol-induced activation of adenylate cyclase in the cellular slime mold, Dictyostelium discoideum.

Binding of cAMP to cell surface receptors evokes the transient activation of of adenylate cyclase in Dictyostelium discoideum. Dithiothreitol is also known as an activator of this enzyme. We found that the dithiothreitol-induced activation was specifically enhanced by extracellular polyamines or divalent cations. Furthermore, EDTA, a chelating agent of divalent cations, completely inhibited the dithiothreitol-induced activation of adenylate cyclase while EDTA did not inhibit the cAMP-induced activation. The inhibition was nullified by addition of polyamines or divalent cations. These results suggest that extracellular polyamines and divalent cations play a specific role in the dithiothreitol-induced activation of adenylate cyclase.

Adenylyl Cyclases↗

PubMed1993

Divalent cation and lipid-protein interactions of biomembranes.

Divalent cations play an important role in the functions of biomembranes. This review deals with three topics: (1) Mg(2+)-mediated change in physical state of phospholipid induces conformation and activity change of reconstituted mitochondrial H(+)-ATPase, (2) a proper transmembrane Ca2+ gradient is essential for the higher enzymatic activity of adenylate cyclase, and (3) role of transmembrane Ca2+ gradient in the modulation of reconstituted sarcoplasmic reticulum Ca(2+)-ATPase activity.

Animals↗

PubMed1976

Images of divalent cations in unstained symmetric and asymmetric lipid bilayers.

Divalent cations have been microscopiccally visualized in association with simple lipid bilayers. Symmetric and asymmetric oriented bilayers were constructed from fatty acid monolayers and were cut in thin transverse sections for examination by bright field electron microscopy in the absence of stains, fixatives or embedding materials. It has been found that bilayers formed of lipid molecules having alkaline earth head groups exhibit natural electron contrast. The intrinsic image has been liked to local variations in the bilayer absolute electron density profile determined by X-ray diffraction analysis of the same specimens (McIntosh, T. J., Waldbillig, R. C. and Robertson, J. D. (1976) Biochim. Biophys. Acta 448, 15-33). By combining the microscopic, chemical and X-ray evidence it has been estimated that local increments of about 1 g/cm3 can produce detectable elelcron contrast in 500 A transverse sections of bilayers.

Barium↗

PubMed1984

Interactions of divalent cations with phosphatidylserine bilayer membranes.

The interaction of divalent cations with a homologous series of diacylphosphatidylserines (diacyl-PS) has been studied by differential scanning calorimetry and X-ray diffraction. Hydrated di-C14-PS (DMPS) exhibits a gel leads to liquid-crystal bilayer transition at 39 degrees C (delta H = 7.2 kcal/mol of DMPS). With increasing MgCl2 concentration, progressive conversion to a phase exhibiting a high melting (98 degrees C), high enthalpy (delta H congruent to 11.0 kcal/mol of DMPS) transition is observed. Similar behavior is observed for DMPS with increasing CaCl2 concentration. In this case, the high-temperature transition of the Ca2+-DMPS complex occurs at approximately 155 degrees C and is immediately followed by an exothermic transition probably associated with PS decomposition. For di-C12-, di-C14-, di-C16- (DPPS), and di-C18-PS, the transition temperatures of the Ca2+-PS complexes are in the range 151-155 degrees C; only di-C10-PS exhibits a significantly lower value, 142 degrees C. A different pattern of behavior is exhibited by DPPS in the presence of Sr2+ or Ba2+, with transitions in the range 70-80 degrees C being observed. X-ray diffraction of the Ca2+-PS complexes at 20 degrees C provides evidence of structural homology. All Ca2+-PS complexes exhibit bilayer structures, the bilayer periodicity increasing linearly from 35.0 A for di-C10-PS to 52.5 A for di-C18-PS. Wide-angle X-ray diffraction data indicate that hydrocarbon chain "crystallization" occurs on Ca2+-PS complex formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Calorimetry, Differential Scanning↗

PubMed1977

The effect of ouabain on the guinea pig ileum longitudinal smooth muscle: 1. ATPase activities in a sarcolemma-enriched fraction prepared with the aid of divalent cation depletion of the intact muscle.

Depletion of divalent cations before fractionation of the longitudinal muscle of the guinea pig ileum yielded a sarcolemma-enriched microsomal fraction free of mitochondria. A major portion of the ATPase activity in the presence of Mg, Na, and K was due to stimulation by Na alone. A further small stimulation by K was demonstrated only in the presence of an activating factor from the 105 000 X g supernatant. Ouabain inhibited only the K activation and had no effect on the Na-stimulated Mg-ATPase.

Adenosine Triphosphatases↗

PubMedDate not supplied

Alkaline phosphatase and ATPases in brush-border membranes of rat jejunum: distinct effects of divalent cations and of some inhibitors.

The effects of divalent cations and of some inhibitors on the activities of alkaline phosphatase and ATPase were examined in rat jejunal brush-border membranes (BBM) isolated by tha Ca(2+)-(BBMCa) or the Mg(2+)-precipitation method (BBMMg). Similar results were found in BBMCa and BBMMg though generally higher in BBMCa. Alkaline phosphatase activity was stimulated by 5 mM MgCl2 (30% to 44%), but not by 5 mM CaCl2 or 0.1 mM ZnCl2, at pH 9.5 or 7.4. ATPase activity was equally stimulated by 5 mM MgCl2 and by 5 mM CaCI2 (about 150%). Alkaline phosphatase activity was significantly inhibited by 1 mM vanadate, 5 mM diamox, 5.0 mM L-leucine and 1 mM theophylline. In contrast, Ca(2+)-ATPase and Mg(2+)-ATPase activities were not depressed by those alkaline phosphatase inhibitors, but were inhibited by 0.1 mM trifluoperazine (more than 70%). 0.1 mM ZnCl2 also appeared to be inhibitory to Ca(2+)-ATPase and Mg(2+)-ATPase, but not to alkaline phosphatase activity even in the presence of Ca2+ and Mg2+. These results suggest that Ca(2+)-ATPase and Mg(2+)-ATPase activities of the rat jejunal BBM are not merely manifestations of alkaline phosphatase, but rather belong to (a) distinct enzyme(s).

Acetazolamide↗

PubMed1985

Rapid axonal transport in Xenopus nerve in divalent cation free media.

An investigation was made of the effects of bathing media low in divalent cations on rapid axonal transport in the sciatic nerve of the amphibian Xenopus laevis. The anterograde transport of a pulse of [35S]methionine proteins was observed using a multiple proportional counter as the detector. Organelles undergoing anterograde and retrograde transport were detected by light microscopy. The structure of nerve fibers was examined by light and electron microscopy. There was no significant difference in the anterograde transport of proteins in nerves bathed in normal medium (NM) containing millimolar Ca2+ and Mg2+ and in those bathed in calcium-free medium (CaFM) containing Mg2+. The anterograde transport of labelled proteins continued at a normal velocity in nerves bathed in divalent cation free medium (DCFM) for at least 14 h. DCFM did cause some alterations in protein transport: the ratio of the plateau (following pulse passage) to the peak radioactivity was increased, the pulse amplitude decreased more rapidly, and the label continued to arrive at the distal end of the nerve for greater than 16 h. Anterograde and retrograde organelle transport continued normally for periods of greater than or equal to 4 h in fibres bathed in DCFM. All myelinated fibres became distorted within 4 h in DCFM. Similar distortion was rare in fibres bathed in CaFM. The results indicate that axonal transport in Xenopus is largely independent of lowered concentrations of divalent cations in the bathing medium. Those alterations in axonal transport that were produced by DCFM may have been secondary to morphological changes in the nerve fibres.

Animals↗

PubMed2001

Simultaneous separation of common mono- and divalent cations on a zirconium-modified silica gel column by ion chromatography with non-suppressed conductimetric detection and tartaric acid-15-crown-5 as eluent.

The application of laboratory-made zirconium-modified silica gels (Zr-silicas) as cation-exchange stationary phases to ion chromatography with conductimetric detection (IC-CD) for common mono- and divalent cations (Li+, Na+, NH4+, K+, Mg2+ and Ca2+) was carried out. Zr-silicas were prepared by the reaction of the silanol group on the surface of silica gel with zirconium tetrabutoxide (Zr(OCH2CH2CH2CH3)4) in ethanol. Zr-silica adsorbed on 10 mg zirconium g(-1) silica gel was a suitable cation-exchange stationary phase in IC-CD for the separation of these mono- and divalent cations. Excellent simultaneous separation and highly sensitive detection for these cations were achieved in 10 min by IC-CD using a Zr-silica column (150x4.6 mm I.D.) and 10 mM tartaric acid containing 10 mM 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane) as the eluent. The proposed IC-CD method was successfully applied to the determination of major mono- and divalent cations in natural water samples.

Cations, Divalent↗

PubMed1997

Extracellular divalent cations block a cation non-selective conductance unrelated to calcium channels in rat cardiac muscle.

1. The effect of removing extracellular divalent cations on resting potential (Vrest) and background conductance of rat cardiac muscle was studied. Vrest was measured with 3 M KCl-filled microelectrodes in papillary muscles, or with a patch electrode in ventricular myocytes. Whole-cell membrane currents were measured in myocytes using step or ramp voltage commands. 2. In both muscles and single cells, decrease or removal of Ca2+o and Mg2+o caused a nifedipine-resistant depolarization, which was reversed upon readmission of Ca2+o or Mg2+o (half-maximal effect at 0.8 mM Ca2+o or 3 mM Mg2+o in muscles). 3. In single myocytes, removal of Ca2+o and Mg2+o had no effect on the seal resistance in nonruptured cell-attached recordings, but reversibly induced a current with a reversal potential (Vrev) of -8 +/- 3.4 mV (with internal Cs+; mean +/- S.E.M., n = 23) during whole-cell recordings. The current was insensitive to nifedipine (3-100 microM) or amiloride (1 mM). Vrev was insensitive to changes in the equilibrium potential for chloride ions (ECl). 4. The current induced in the absence of extracellular divalent cations was blocked in a concentration-dependent manner by Ca2+o. (At -80 mV, the affinity constant KCa was 60 microM with a Hill coefficient of 0.9) KCa was voltage dependent at positive but not negative potentials. Mg2+o, Ni2+o, Sr2+o, Ba2+o, Cd2+o and Gd3+o also blocked the current. 5. In 0 mM Na+ (145 mM NMDG+), the inward component of the divalent cation-sensitive current was decreased and Vrev shifted to more negative potentials. 6. These results suggest that a novel conductance pathway, permeable to monovalent cations but not to Cl- and blocked by divalent cations, exists in ventricular myocytes.

Amiloride↗

PubMed1984

Mass-action formulations of monovalent and divalent cation adsorption by phospholipid membranes.

An extension of a previous treatment (Cohen, J. A., and M. Cohen, 1981, Biophys. J., 36:623-651) is presented for the adsorption of monovalent and divalent cations by single-component phospholipid membranes, where monovalent cations adsorb with a cation/phospholipid stoichiometry of 1:1 and divalent cations adsorb with stoichiometries of 1:1 and 1:2. Previously the 1:1 and 1:2 binding of divalent cations were assumed to occur by independent, parallel pathways. Here a serial adsorption scheme is considered in which 1:2 binding occurs via reaction of 1:1-bound complexes with adjacent unoccupied phospholipids. This two-dimensional lattice reaction is shown to obey a law of mass action, and the mass-action equilibrium constant is used to parameterize the adsorption isotherm. This isotherm is shown to be mathematically equivalent to the previous isotherm, although the two formulations differ in the dependence of 1:2 binding on the 1:1 association constant.

Cations, Divalent↗

PubMed2005

Treatment failures secondary to drug interactions with divalent cations and fluoroquinolone.

We observed four cases of therapeutic failures while patients were simultaneously taking medications that contained divalent cations and oral fluoroquinolones. Patients improved after conversion to the intravenous formulation of the same antibiotics, proper spacing of the divalent cation, or conversion to a different antibiotic class. Patients prescribed oral fluoroquinolones should receive instructions on proper separations of these antibiotics with divalent cations. Health care professionals should be cognizant of these interactions and educated on their potential deleterious effect.

Administration, Oral↗

PubMed1995

Activation of p58c-fgr and p53/56lyn in adherent human neutrophils: evidence for a role of divalent cations in regulating neutrophil adhesion and protein tyrosine kinase activities.

Tumor necrosis factor (TNF) stimulates generation of reactive oxygen intermediates, secretion of granule constituents, and rearrangement of the cytoskeleton in neutrophils (PMN); this response requires that PMN be adherent to plasma or extracellular matrix proteins, and is dependent on beta 2 integrins. Tyrosine phosphorylation of distinct proteins [Fuortes et al., J Cell Biol 120:777-784, 1993] and activation of the protein tyrosine kinase p58c-fgr [Berton et al., J Cell Biol 126:1111-1121, 1994] were recently recognized as signals involved in beta 2 integrin-dependent responses of TNF-treated PMN. As the integrin capability to bind their ligands is regulated by divalent cations we investigated whether modulation of PMN adhesion to fibrinogen by divalent cations also affected activation of protein tyrosine kinases. In the absence of divalent cations or in the presence of Ca2+ alone, PMN did not adhere to fibrinogen in response to TNF. However, Mg2+, either alone or together with Ca2+, promoted stimulated adhesion to fibrinogen. We also found that Mn2+ promoted PMN adhesion to fibrinogen without additional stimuli. Analysis of the activity of two src family tyrosine kinases, p58c-fgr and p53/56lyn, showed that their autophosphorylating kinase activity strictly correlated with adhesion. In fact, only in the presence of Mg2+, but not in the absence of divalent cations or in the presence of Ca2+ alone, TNF increased p58c-fgr and p53/56lyn kinase activities; and this was prevented by anti-CD18 antibodies. In addition, Mn2+ strongly promoted activation of p58c-fgr and p53/56lyn without additional stimuli. Analysis of tyrosine phosphorylated proteins with anti-phosphotyrosine immunoblots showed that divalent cations regulated adhesion and protein tyrosine phosphorylation in the same fashion. Detergent extraction of proteins showed that the Mg(2+)-dependent, TNF-stimulated adhesion redistributed p58c-fgr and p53/56lyn to a Triton-insoluble fraction. In addition, analysis of p58c-fgr activity allowed us to demonstrate that the fraction of p58c-fgr which became Triton-insoluble displayed a higher kinase activity. These findings establish that PMN adhesion signals for activation of two different src family tyrosine kinases. The evidence that Mn2+, a strong promoter of integrin function, induces adhesion and activation of tyrosine kinases without additional stimuli suggest the existence of a direct link between beta 2 integrins binding to fibrinogen and activation of tyrosine kinases in neutrophils.

Antibodies↗

PubMed1986

Effects of membrane depolarization and divalent cations on anaphylactic histamine secretion.

The effects of membrane depolarization and divalent cations on histamine release have been studied in sensitized mast cells. Membrane potential of these cells has been measured with intracellular microelectrodes. Our results show that mast cells have a large resting potential (-61 +/- 12 mV) however they do not generate active membrane electrical responses when are depolarized by passing current through the recording microelectrode. High external K+ does not increase histamine release. Histamine secretion is supported by alkali-earth divalent cations (Ca2+ greater than Sr2+ greater than Ba2+) but strongly inhibited by transition metals. Ca2+ concentrations above 1 mM inhibit histamine release, however, this effect is not mimicked by Sr2+ and Ba2+.

Anaphylaxis↗

PubMed1981

Adsorption of divalent cations to bilayer membranes containing phosphatidylserine.

The Stern equation, a combination of the Langmuir adsorption isotherm, the Boltzmann relation, and the Grahame equation from the theory of the diffuse double layer, provides a simple theoretical framework for describing the adsorption of charged molecules to surfaces. The ability of this equation to describe the adsorption of divalent cations to membranes containing brain phosphatidylserine (PS) was tested in the following manner. Charge reversal measurements were first made to determine the intrinsic 1:1 association constants of the divalent cations with the anionic PS molecules: when the net charge of a PS vesicle is zero one-half of the available sites are occupied by divalent cations. The intrinsic association constant, therefore, is equal to the reciprocal of the divalent cation concentration at which the mobility of a PS vesicle reverses sign. The Stern equation with this association constant is capable of accurately describing both the zeta potential data obtained with PS vesicles at other concentrations of the divalent cations and the data obtained with with vesicles formed from mixtures of PS and zwitterionic phospholipids. Independent measurements of the number of ions adsorbed to sonicated PS vesicles were made with a calcium-sensitive electrode. The results agreed with the zeta potential results obtained with multilamellar vesicles. When membranes are formed at 20 degrees C in 0.1 M NaCl, the intrinsic 1:1 association constants of Ni, Co, Mn, Ba, Sr, Ca, and Mg with PS are 40, 28, 25, 20, 14, 12, and 8 M-1, respectively.

Cations, Divalent↗

PubMed1998

Bacillus subtilis cells lacking penicillin-binding protein 1 require increased levels of divalent cations for growth.

Bacillus subtilis strains lacking penicillin-binding protein 1 (PBP1), encoded by ponA, required greater amounts of Mg2+ or Ca2+ for vegetative growth or spore outgrowth than the wild-type strain and strains lacking other high-molecular-weight (HMW) PBPs. Growth of ponA cells in a medium low in Mg2+ also resulted in greatly increased cell bending compared to wild-type cells or cells lacking other HMW PBPs. The addition of high levels of Mg2+ to growth media eliminated these phenotypes of a ponA mutant. In contrast to the effects of divalent cations, NaCl did not restore ponA cell growth in a divalent-cation-deficient medium. Surprisingly, wild-type cells swelled and then lysed during both vegetative growth and spore outgrowth when 500 mM NaCl was included in a divalent-cation-deficient medium. Again, Mg2+ addition was sufficient to allow normal vegetative growth and spore outgrowth of both wild-type and ponA cells in a medium with 500 mM NaCl. These studies demonstrate that (i) while HMW PBPs possess largely redundant functions in rich medium, when divalent cations are limiting, PBP1 is required for cell growth and spore outgrowth; and (ii) high levels of NaCl induce cell lysis in media deficient in divalent cations during both vegetative growth and spore outgrowth.

Bacillus subtilis↗