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At least 19 recordsLinked to original sources
PubMed1976

Permeability of a cell junction during intracellular injection of divalent cations.

Divalent cations are microinjected into Chironomus salivary gland cells while the cell-to-cell passage of fluorescein (330 dalton) and electrical coupling are monitored. Injections of Ca and Mg that substantially depolarize the cells produce block or marked slowing fluorescein passage, accompanied by electrical uncoupling. Injections of Ca, Mg or Sr that cause little depolarization, and presumably smaller elevation of divalent cation concentration in the cytoplasm, produce block or marked slowing of fluorescein passage with little or no detectable electrical uncoupling. This partial uncoupling may reflect total closure of a fraction of the channels in junctional membrane or partial closure of all channels.

Animals↗
PubMed1976

Magnesium withdrawal and contraction of arterial smooth muscle: effects of EDTA, EGTA, and divalent cations.

The divalent cation chelators, CaEDTA and EGTA, were demonstrated to exert opposite effects on contractions of rat aortic smooth muscle induced by withdrawal of external magnesium ([Mg2+]0). Addition of CaEDTA potentiated such contractions more than 100%, while EGTA promoted rapid relaxation. Rapid relaxation of contractions induced by withdrawal of [Mg2+]0 could also be induced by Mn, Ni, and Cd but not Sr. Using EC50's, a relative descending order of contractile inhibition was noted for the divalent cations: Mn greater than Cd greater than Mg greater than Ni. The ability of CaEDTA to potentiate contractions produced by withdrawal of [Mg2+]0, as well as the ability of divalent cations to relax contractions of aortic smooth muscle, appears to be related to actions on the transmembrane flux of Ca2+. These findings thus lend support to the view that Mg ions either play an important role in regulating membrane permeability to [Ca2+]0 or occupy membrane sites which are exchangeable with membrane-bound Ca in certain types of aterial smooth muscle.

Animals↗
PubMed1977

The effect of monovalent and divalent cations on the activity of Streptococcus lactis C10 pyruvate kinase.

The pyruvate kinase (ATP: pyruvate 2-O-phosphotransferase, EC 2.7.1.40) from Streptococcus lactis C10 had an obligatory requirement for both a monovalent cation and divalent cation. NH+4 and K+ activated the enzyme in a sigmoidal manner (nH =1.55) at similar concentrations, whereas Na+ and Li+ could only weakly activate the enzyme. Of eight divalent cations studied, only three (Co2+, Mg2+ and Mn2+) activated the enzyme. The remaining five divalent cations (Cu2+, Zn2+, Ca2+, Ni2+ and Ba2+) inhibited the Mg2+ activated enzyme to varying degrees. (Cu2+ completely inhibited activity at 0.1 mM while Ba2+, the least potent inhibitor, caused 50% inhibition at 3.2 mM). In the presence of 1 mM fructose 1,6-diphosphate (Fru-1,6-P2) the enzyme showed a different kinetic response to each of the three activating divalent cations. For Co2+, Mn2+ and Mg2+ the Hill interaction coefficients (nH) were 1.6, 1.7 and 2.3 respectively and the respective divalent cation concentrations required for 50% maximum activity were 0.9, 0.46 and 0.9 mM. Only with Mn2+ as the divalent cation was there significatn activity in the absence of Fru-1,6-P2. When Mn2+ replaced Mg2+, the Fru-1,6-P2 activation changed from sigmoidal (nH = 2.0) to hyperbolic (nH = 1.0) kinetics and the Fru-1,6-P2 concentration required for 50% maximum activity decreased from 0.35 to 0.015 mM. The cooperativity of phosphoenolpyruvate binding increased (nH 1.2 to 1.8) and the value of the phosphoenolpyruvate concentration giving half maximal velocity decreased (0.18 to 0.015 mM phosphoenolyruvate) when Mg2+ was replaced by Mn2+ in the presence of 1 mM Fru-1,6-P2. The kinetic response to ADP was not altered significantly when Mn2+ was substituted for Mg2+. The effects of pH on the binding of phosphoenolpyruvate and Fru-1,6-P2 were different depending on whether Mg2+ or Mn2+ was the divalent cation.

Adenosine Diphosphate↗
PubMed1976

The role of divalent cations in activation of the sea urchin egg. I. Effect of fertilization on divalent cation content.

The Ca and Mg content of unfertilized sea urchin eggs (3 and 21 mumole/ml eggs) remains remarkably constant over periods of hours, even when the eggs are suspended in Ca- or Mg-free sea water. After fertilization the Ca content of eggs in regular sea water increases sharply by about 20%, followed by a decrease to the unfertilized level by 40 minutes. However, if the fertilized eggs are washed three minutes in Ca-free sea water a sharp decrease in the Ca content occurs amounting to 30% of the total in the first 40 minutes, with little change thereafter. Suspension of the eggs in Ca-free sea water results in an even greater loss of Ca amounting to about 43% of the total in the same time interval, followed by a continuing slow loss. It is concluded that fertilization initiates the intracellular release of Ca, which is then extruded. For unwashed eggs this change is masked by the simultaneous generation of new extra-cellular coats with high affinity for Ca. Changes in the Mg content of fertilized eggs follow the same general pattern except that absorption of this divalent cation to the extracellular coats is minimal.

Animals↗
PubMed1978

Ethanol: modifications of acute intoxication by divalent cations.

Calcium, other divalent cations, and calcium antagonists were tested for their ability to alter ethanol-induced sleeping time, hypothermia, and behavioral intoxication in mice and rats. Calcium given intraventricularly significantly enhanced sleeping time and behavioral intoxication in a dose-related manner. The ionophores X537A and A23187 accentuated the effect of a low dose of calcium, whereas the calcium chelators EDTA and EGTA decreased sleeping time. Calcium also enhanced tertiary butanol- and chloral hydrate-induced sleeping time. The effects of cations on ethanol-induced hypothermia were less significant. The results suggest the existence of a central calcium pool that is involved in ethanol intoxication in rodents.

Alcoholic Intoxication↗
PubMed1979

Effects of divalent cations on thermophilic inorganic pyrophosphatase.

Divalent cations were shown to affect the structure and thermostability of thermophilic inorganic pyrophosphatase [pyrophosphate phosphohydrolase EC 3.6.1.1] purified from Bacillus stearothermophilus and thermophilic bacterium PS-3. The properties of the enzymes from the two sources were found to be very similar. The enzymes were very unstable to heart in the absence of divalent cations, being inactivated gradually even at 40 degrees C. However, they became stable to heat denaturation in the presence of Mg2+, between pH 7.8 and 9.0. Similar induced thermostability was detected when Mn2+, Co2+, Ca2+, Cd2+, and ZN2+ were added, though the latter three cations were not essential for enzyme activity. On adding divalent cations, the optical properties such as absorption spectra, fluorescence spectra, and circular dichroism (CD) were changed. Gel filtration and disc electrophoresis revealed that the molecular weight of both enzymes was 5.4 x 10(4) in Tris-SO4 buffer and 11 x 10(4) in Tris-HCL buffer, suggesting monomer-dimer transformation. In the presence of divalent cations in Tris-SO4 fuffer, the enzymes dimerized; this was confirmed by sedimentation velocity measurements. The enzymes in Tris-HCL buffer did not show thermostability unless divalent cations were added. The results in the present study indicate that binding of divalent cations to each enzyme caused some conformational change in the vicinity of aromatic amino acid residues leading to dimerization of the enzyme molecule so that it became thermostable. It was also suggested that histidyl residues play an important role in the thermostability induced by divalent cations on the basis of the pH dependencies of thermostability and CD spectra.

Bacteria↗
PubMed1979

Calculation of the concentrations of free cations and cation-ligand complexes in solutions containing multiple divalent cations and ligands.

The method described permits the computation of the concentrations of free ions and ion-ligand complexes in a solution containing arbitrary numbers of divalent cations and ligands. It is required that the pH be known, along with appropriate sets of ligand-hydrogen and ligand-divalent cation concentration binding constants. It is assumed that these sets of constants are chosen to be consistent with the ionic strength of the complete solution which contains the divalent cations and ligands. The technique is an iterative one which provides upper and lower bounds for the values of the unknowns. The method does not require initial guesses at the values of the unknowns, and it gives correct answers even when the concentrations involved are many orders of magnitude apart. The present formulation of the problem is restricted to the case where only one cation can bind to a given ligand at any one time. The method is applicable to large molecules with multiple "sub-ligands" provided these sub-ligands are independent in their function as ion-binding sites. These sub-ligands need not all have the same properties. It is also shown that a simple modification of the method permits the determination of the subset of total ion concentrations that are required in order to produce a specified subset of free ion concentrations. The modifications required to include monovalent cation binding are presented in outline form.

Adenosine Triphosphate↗
PubMed1992

Ionic modulation of the effects of heparin on plasminogen activation by tissue plasminogen activator: the effects of ionic strength, divalent cations, and chloride.

Ionic strength, divalent cations, and Cl- modulate the ability of the glycosaminoglycan heparin to stimulate the activation of human plasminogen (Pg) by tissue-type Pg activator. Kinetic analysis of Pg activation indicates that heparin is inhibitory, stimulatory, or nonstimulatory as a function of ionic strength. While increasing ionic strength inhibits Pg activation in the absence of heparin, in it presence an activation phase followed by an inhibitory phase is observed. Divalent cations, inhibitors of activation in the absence of heparin, increase the rate of activation in its presence. Kinetic analysis demonstrates that divalent cations augment the heparin stimulatory effect a maximum of 60-fold due to increases in kcat without changes in Km of the reaction. This effect is heparin-specific, since activation is not affected by Ca2+ in the presence of heparan sulfate or de-N-sulfated heparin. Also, Cl- inhibits Pg activation in the presence of heparin by acting as a competitive inhibitor (Kic of 100 mM). Furthermore, inhibition by Cl- reduces the overall magnitude of heparin stimulation of Pg activation. These results suggest that physiologic ions in combination with heparin may be significant effectors of Pg activation in the vascular microenvironment.

Binding, Competitive↗
PubMed1976

Interference stimulated by tick-borne encephalitis virus: influence of divalent cations.

The effects of divalent cations (barium, cobalt, calcium, copper, magnesium, zinc and iron) on the interference of tick-borne encephalitis (TE) virus with vaccinia virus in Detroit-6 cell cultures were investigated. An increase in interference was shown in the presence of cobalt, zinc, copper, and magnesium. Barium and iron displayed a marked inhibitory action. But an increase in interference was not parallel with an increased production of interferon.

Barium↗
PubMed1977

Divalent cation binding to phospholipids: an EPR study.

Divalent cation association to sonicated phospholipid liposomes has been examined with electron paramagnetic spectroscopy. Spectra were obtained suggesting that, in some cases, divalent cations associated with acidic phospholipid head groups are highly mobile. Using the amplitude of its characteristic sextet signal as a measure of free Mn(H2O)+6+, the apparent affinities of cardiolipin and phosphatidylserine for Mn2+ were measured as a function of monovalent electrolyte. Monovalent cations having smaller nonhydrated radii were more effective in displacing Mn from the phospholipids. Under conditions of low divalent cation concentrations, it is shown that the Gouy-Chapman diffuse double layer theory predicts a Mn-affinity (KA) inversely proportional to the square of monovalent salt concentration. Although this relationship was closely obeyed for Mn binding to cardiolipin, the fall-off in KA with added sodium chloride was slower in the cases of Mn binding to phosphatidylserin or phosphatidic acid. When phosphatidylcholine or cholesterol was incorporated into mixed vesicles along with a fixed amount of charged phospholipid, the Mn-binding strength was roughly proportional to the weight fraction of the latter. This result is consistent with: (1) a random dispersal of lipids in the bilayer, and (2) a 1:2 divalent cation-phospholipid interaction.

Binding Sites↗
PubMed1975

The effect of divalent cations on bovine spermatozoal adenylate cyclase activity.

The effect of divalent cations on bovine sperm adenylate cyclase activity was studied. Mn2+, Co2+, Cd2+, Zn2+, Mg2+ and Ca2+ were found to satisfy the divalent cation requirement for catalysis of the bovine sperm adenylate cyclase. These divalent cations in excess of the amount necessary for the formation of the metal-ATP substrate complex were found to stimulate the enzyme activity to various degrees. The magnitude of stimulation at saturating concentrations of the divalent cations was strikingly greater with M2+ than with either Ca2+, Mg2+, Zn2+, Cd2+ or Co2+. The apparent Km was lowest for Zm2+ (0.1 - 0.2 mM) than for any of the other divalent cations tested (1.2 - 2.3 mM). The enzyme stimulation by Mn2+ was decreased by the simultaneous addition of Co2+, Cd2+, Ni2+ and particularly Zn2+ and Cu2+. The antagonism between Mn2+ and Cu2+ or Zn2+ appeared to have both competitive and non-competitive features. The inhibitory effect of Cu2+ on Mn2+-stimulated adenylate cyclase activity was prevented by 2,3-dimercaptopropanol, but not by dithiothreitol, L-ergothioneine, EDTA, EGTA or D-penicillamine. Ca2+ at concentrations of 1-5 mM was found to act synergistically with Mg2+, Zn2+, Co2+ and Mn2+ in stimulating sperm adenylate cyclase activity. The Ca2+ augmentation of the stimulatory effect of Zn2+, Co2+, Mg2+ and Mn2+ appeared to be specific.

Adenylyl Cyclases↗
PubMed1978

Ionization and divalent cation dissociation constants of nalidixic and oxolinic acids.

The ionization constants and some divalent cation dissociation constants of nalidixic and oxolinic acids, both specific inhibitors of bacterial DNA replication, have been determined. The carboxylic pKa' values are 6.1 and 6.9 at 25 degrees for nalidixic and oxolinic acids, respectively. These values indicate that intramolecular hydrogen-bonding stabilizes the un-ionized form of these compounds in aqueous solution. Both compounds bind divalent cations; the divalent cation dissociation constants for oxolinic acid are somewhat smaller that those for nalidixic acid. We suggest that both compounds may act by forming a complex in situ with a divalent cation in a metalloprotein involved in DNA replication. The evidence that both drugs inhibit at the same target site is briefly reviewed.

Cations, Divalent↗
PubMed1992

Modulation of (+)-[3H]pentazocine binding to guinea pig cerebellum by divalent cations.

The ability of cations to modulate the binding of the sigma 1 receptor-selective ligand (+)-[3H]pentazocine to guinea pig cerebellum was investigated. Di- and trivalent cations biphasically inhibited (+)-[3H]pentazocine binding, revealing multiple affinity states. The rank order of potency of these cations (based on the high affinity component of inhibition) was Zn2+ > Co2+ >> La3+ = Ni2+ = Cd2+ = Mn2+ = Gd2+ > Ba2+ = Sr2+ >> Mg2+ > Ca2+. The inhibition of 1,3-[3H]di(2-tolyl)guanidine binding to the sigma 2 receptor by these cations differed qualitatively and quantitatively from their effects on (+)-[3H]pentazocine binding. Although monovalent cations decreased the Kd for (+)-[3H]pentazocine binding, divalent cations split (+)-[3H]pentazocine binding into low and high affinity components. The Bmax of the high affinity component decreased with increasing divalent cation concentrations. Both mono- and divalent cations significantly reduced the rate of association of (+)-[3H]pentazocine with the sigma 1 receptor without altering the dissociation rate. (+)-[3H]Pentazocine binding was not altered by guanine nucleotides or by treatment with cholera or pertussis toxins. However, nonselective cation channel blockers (cinnarizine, hydroxyzine, prenylamine, amiodarone, and proadifen) potently inhibited (+)-[3H]pentazocine binding. These results indicate that physiologically relevant concentrations of divalent cations allosterically modulate (+)-[3H]pentazocine binding to the sigma 1 receptor, to reveal multiple affinity states. These sites do not represent sigma 1 to sigma 2 subtype interconversion or ternary complex formation with guanine nucleotide-binding proteins. However, the rank order of cation potency and the inhibition of binding by cation channel blockers is consistent with a potential role for sigma receptors as constituents of cation channels.

Animals↗
PubMed1979

Effects of divalent cation ionophores on the neuron membrane of the crayfish.

The effects of divalent cation ionophores, A23187 and X-537A, on the electrical membrane properties were investigated by using the soma membrane of the X-organ of the crayfish. They reduced the amplitude and maximum rate of rise of Ca-action potential in lower concentration. As the concentration increased, a reduction of membrane resistance and hyperpolarization occurred simultaneously. Further increase resulted in membrane depolarization with a further decrease in resistance. The threshold concentration of X537A was 100 times higher than that of A23187. These effects were reversible only when the application period was relatively short, while a longer application resulted in an incomplete reversibility or in no reversibility at all. The ionophore effect was facilitated in high Ca medium and diminished in low Ca medium. In Sr medium, the same effects on the resistance and the membrane potential were barely observable. TEA reduced the effects of A23187 but did not completely inhibit the effects. The Na-cation potential was also reduced by the higher concentration of the ionophore. From these results it is concluded that the divalent cation ionophores. A23187 and X537A, carry divalent cations, Ca ions in a physiological medium, into the neuron soma through the membrane and the consequent increase of the intracellular divalent cations induces K conductance increase and that higher concentration of the ionophore induces the increase in the conductance of the other ion species, such as Na.

Action Potentials↗
PubMed1978

Effects of cerebroventricular perfusion with monovalent and divalent cations on plasma cortisol of conscious cats.

The effects of altering the concentrations of various cerebrospinal fluid (CSF) cations on hypothalamo-hypophyseal-adrenocortical (HHA) activity were investigated in conscious cats. The cerebroventricles were perfused with CSF containing high or low [Na+], [K+], [Li+], [Ca2+] and [Mg2+] for 60 min and plasma samples taken periodically for analysis of cortisol. The results demonstrate that changing CSF [Na+] or [Li+] does not substantially alter plasma cortisol levels. Although individually elevating CSF [K+], [Ca2+] or [Mg2+] does not affect plasma cortisol levels, reducing these CSF cations activates the HHA system and the latter in turn is inhibited by the addition of dexamethasone (DEX) to low cation CSF. The excitatory action of reduced [Ca2+] is also inhibited by the addition of norepinephrine to the perfusion fluid, suggesting that lowering this cation affects the HHA system by preventing the release of the adrenergic neurotransmitter. Furthermore, these data suggest that in conscious unrestrained cats basal HHA activity is dependent to some extent upon normal brain extracellular [K+], [Ca2+] and [Mg2+].

Animals↗