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PubMed1980

Effects of divalent cations on collagen biosynthesis in isolated chick embryo tendon cells.

Isolated chick embryo tendon cells were used in [14C]proline and [14C]lysine labelling experiments to investigate the effect of divalent cations on collagen biosynthesis with a special reference to prolyl hydroxylation and lysyl modifications. The following metals were studied by adding them to the incubation medium of the cells: Ca2+, Cd2+, Co2+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+ and Zn2+. Zn2+ caused a potent reductin in collagen prolyl hydroxylation with a concomitant increased cellular retention of collagenase-digestible material. These effects were detectable even at physiological concentrations. At the same concentrations of Zn2+, lysyl hydroxylation was considerably less inhibited than prolyl hydroxylation, and the extent of hydroxylysyl glycosylation was even increased. Co2+ was also an efficient inhibitor of collagen prolyl hydroxylation, but at concentrations ten times higher than those of Zn2+. In the presence of other metal ions, no or only up to 10% inhibition of prolyl hydroxylation was noted even at those concentrations at which [14C]proline incorporation into the protein was decreased. However, an increased cellular retention of collagen was detected in the presence of some metal ions. No reduction in lysyl hydroxylation was found in the presence of Ca2+ or Mg2+.

Animals↗
PubMed1995

Modification of gap junction conductance by divalent cations and protons in neonatal rat heart cells.

Myocytes were isolated from neonatal rat hearts and grown in culture dishes. Pairs of cells were selected to study the effect of divalent cations and protons on the conductance of gap junctions, gj. The experimental approach involved the dual voltage-clamp method and cell dialysis via patch pipette, i.e. gj was monitored while the cytosolic level of Ca2+, Mg2+, Sr2+, Ba2+ or H+ was modified in one of the cells. A dose-dependent decrease in gj developed when pCa of the pipette solution was lowered (range: pCa = 7.7-2.42, equivalent to a [Ca2+] of 20 nM-3.8 mM). The gj/pCa-relationship revealed a Hill coefficient n of 0.87 and a half-maximal concentration pKCa of 3.5. Pretreatment with 3 mM NiCl2 and 1 micron ryanodine to minimize the removal of cytosolic Ca2+ did not significantly affect the response to gj. Similarly, gj was decreased in a dose-dependent fashion when pHi in the pipette solution was lowered (range: pH = 7.2-5.0, corresponding to a [H+] of 63 nM-10 microns). The gj/pH-relationship yielded an n of 0.92 and a pKH of 5.85. Pretreatment with 1 mM amiloride to minimize the extrusion of protons enhanced the effects of pH on gj. Simultaneous alterations in pCa and pH demonstrated an additive type of action of Ca2+ and H+ on gj. This is consistent with the existence of two types of sensors which contribute separately to the functional state of gj. No significant decrease in gj was detectable when the pipette solution contained Mg2+ or Ba2+ (up to 5 mM). Partial uncoupling was observed with pipette solution containing 5 mM Sr2+. We conclude that gj of neonatal and adult cardiomyocytes exhibit different ionic sensitivities. This discrepancy may reflect differences in connexin expression and/or molecular intermediates involved in regulating gj.

Aging↗
PubMed2001

Modulation by divalent cations of GABA rho 1 receptor from human retina expressed in Xenopus oocytes.

OBJECTIVE: To investigate functional homooligomeric GABA rho 1 receptors expressed in Xenopus oocytes and the modulation of divalent cations. METHODS: GABA rho 1 cDNA from human retina was transcribed in vitro to obtain sense rho 1 mRNA, which was microinjected into Xenopus oocytes. Two-electrodes voltage clamp technique was performed to record GABA-induced currents. RESULTS: Expressed receptors were found to have similar properties to GABAc receptors characterized in the retina. Cl-currents induced by GABA were blocked by picrotoxin instead of bicuculline. GABA-induced currents reversed at -19 +/- 2.5 mV, and EC50 was 3.3 mumol/L. Zn++ modulated GABA-induced currents with an IC50 = 9.6 mumol/L. Ni++, Cu++ and Cd++ inhibited GABA rho 1 obviously, too. Their rank order of potency was Zn++ > Ni++ > Cu++ > Cd++. CONCLUSION: Zinc (10 mumol/L) inhibited GABA-induced currents in a competitive manner, and its action was sensitive to extracellular pH. Site-directed mutagenesis revealed that substitution of a single histidine residue (H44 and H48) failed to affect zinc sensitivity.

Animals↗
PubMed1983

Effects of manganese and other divalent cations on calcium uptake and catecholamine secretion by primary cultures of bovine adrenal medulla cells.

Primary cultures of bovine adrenal medullary chromaffin cells were used to examine the effect of replacing divalent cations in the extracellular media on secretion. When calcium was replaced by manganese, nicotine-stimulated secretion was delayed in onset for 3 to 5 minutes, but continued for approximately 60 minutes. In contrast, calcium-supported secretion began immediately on stimulation and plateaued by 10 minutes. 54Mn2+ uptake occurred on stimulation but at a lower rate than 45Ca2+ uptake. There was no delay of 54Mn2+ uptake upon stimulation and 54Mn2+ uptake was considerably prolonged compared to 45Ca2+ uptake. Replacement of calcium with strontium gave results similar to those with calcium, and, in addition, strontium was able to bring about secretion by itself in a manner similar to barium. Inhibition experiments showed that the potency for inhibiting calcium uptake was Cd2+ greater than Mn2+ greater than Ca2+ greater than Sr2+.

Adrenal Medulla↗
PubMed1988

Calcium: a program in BASIC for calculating the composition of solutions with specified free concentrations of calcium, magnesium and other divalent cations.

A BASIC program is presented which facilitates the formulation of biologically relevant chemical solutions containing specified free concentrations of as many as three divalent metal cations (Ca2+, Mg2+ and the choice of a third divalent cation) at any pH in the presence of as many as three ligands (EGTA, ATP and GTP). The program uses the law of mass action and the absolute stability (association) constants found in the literature to calculate the total concentration of divalent metal cation needed to achieve a desired free concentration. The user enters the pH, the concentrations of the ligands used and the desired free concentrations of the divalent cations. This program was developed for use in a wide range of biological applications, particularly the rapid design of solutions which mimic certain aspects of intracellular fluid.

Adenosine Triphosphate↗
PubMed2005

Adsorption and thermochemical data of divalent cations onto silica gel surface modified with humic acid at solid/liquid interface.

Humic acid immobilized onto silica gel surface was studied by the calorimetric titration of divalent cations in aqueous solution. The adsorption isotherms were obtained by the batchwise method and were fitted to a modified Langmuir equation. The maximum number of moles per gram of the material gave: 10.42+/-0.75, 13.16+/-0.58, 7.87+/-0.58 for copper, nickel and zinc, respectively. Gibbs free energies were negative for all systems and the adsorption interactions calorimetrically followed presented endothermic enthalpic values: 6.24+/-0.47, 6.75+/-0.74, 6.97+/-0.58 kJ mol-1 for the same sequence of divalent cations. All liquid/solid interface adsorptions were entropically driven.

Adsorption↗
PubMed2005

The structural events associated with the binding of divalent cations to beta-bungarotoxin.

In order to address the mechanism why the Ca2+ was crucial for the manifestation of the phospholipase A2 (PLA2) activity of beta-bungarotoxin (beta-BuTx), four divalent cations were used to assess their influences on the catalytic activity and the fine structures of beta-BuTx. Substitution Mg2+ or Sr2+ for Ca2+ in the substrate solution was found to cause a decrease in the PLA2 activity to approximately 15 or 6% of that in the presence of Ca2+. However, only marginally detectable PLA2 activity was observed with the addition of Ba2+. The nonpolarity of 8-anilinonaphthalene-1-sulfonate (ANS)-binding site of beta-BuTx markedly increased with the binding of cations to beta-BuTx. The negative ellipticity noted with the CD spectra of beta-BuTx increased upon the binding of cations too. With the exception of Ba2+, the order of the ability of cations to enhance the intensity of ANS fluorescence or increase the increment of negative ellipticity was Sr2+ > Ca2+ > Mg2+, which was the same order as the increase in their atomic radii. However, the energy transfer from Trp fluorescence emission to ANS was most effective upon the addition of Ca2+. Moreover, the extent of glutaraldehyde crosslinking between A chain and B chain decreased in the presence of cations. Nevertheless, the binding affinities of beta-BuTx for the four cations were similar. These results, together with the findings that the ANS molecule binds at the active site of the A chain in beta-BuTx, suggest that the binding of Ca2+ to beta-BuTx induces subtly conformational changes occurred at the active site for exerting the activity of beta-BuTx. Moreover, the change in the gross conformation induced by the binding of Ca2+ may affect the interaction between A chain and B chain, and consequently the activity of beta-BuTx as well.

Barium↗
PubMed1983

Photoreceptor disc shedding in eye cups. Inhibition by deletion of extracellular divalent cations.

To further define the medium requirements for in vitro rod disc shedding and phagocytosis in eye cups of Xenopus laevis, the effect of deletion of divalent cations was examined. Calcium-free medium completely eliminated both normal diurnal disc shedding (initiated by light onset) and dark-primed disc shedding (initiated by a period of darkness followed by additional darkness or light). The effect was reversible. Furthermore, the events that occurred during the initial dark-priming period did not require extracellular millimolar calcium, since the addition of calcium (1.8 mM) after an initial hour of darkness in calcium-free medium resulted in a marked increase in disc shedding, regardless of the subsequent lighting condition. Magnesium-free medium did not inhibit light-evoked shedding. However, magnesium-free medium partially inhibited disc shedding in one of the two lighting paradigms used to elicit dark-primed disc shedding. This suggests that the extracellular divalent cation requirement varies for different lighting paradigms that promote shedding. The inhibition of disc shedding by magnesium-free medium was morphologically distinct from calcium-free medium; the inhibition in magnesium-free medium was correlated uniquely with a reduction in the interdigitation between the photoreceptor and the retinal pigment epithelium.

Animals↗
PubMed1983

Effect of divalent cations and chelators on metaphase to telophase progression and nuclear envelope formation in Chinese hamster cells.

Chinese hamster DON cells in log phase were treated with Colcemid in the G2 period with or without divalent cation chelating agents. The metaphase cells were isolated and incubated in two ways: 1) without Colcemid but with chelating agents or La3+ and observed for metaphase to telophase progression, and 2) with Colcemid, with or without chelating agents and the rate of micronuclei formation in the absence of anaphase monitored. The effect of the chelating agents on cellular 45Ca2+ during metaphase to telophase progression was also studied. The results indicate that Ca2+ and possibly Mg2+ ions are involved in the regulation of certain segments of mitosis. The reduction of environmental and plasma membrane associated Ca2+ with the chelators and La3+ promoted the metaphase to telophase progression as well as nuclear envelope and micronuclei formation.

Animals↗
PubMed1997

Modulation of the ER Ca2+ channel BCC1 from tendrils of Bryonia dioica by divalent cations, protons and H2O2.

Electrical properties of the ER Ca2+ channel BCC1 from tendrils of Bryonia dioica were analyzed after incorporation of BCC1 into black lipid bilayers. Single channel current fluctuations were modulated by divalent cations, protons and H2O2. Whereas the channel is permeable for Ca2+, Ba2+ and Sr2+, its conductance is strongly reduced in solutions containing MgCl2. Cu2+ and Zn2+ are potent inhibitors of BCC1 in micromolar concentrations. The open channel conductance of BCC1 increases with acidification of the electrolyte solution. H2O2 shows strong inhibitory effects on BCC1. The channel is almost completely closed at submillimolar concentrations of H2O2. The effects of pH and H2O2 on channel properties are directional and affect BCC1 at the Ca exit side, but not on the entry site. Thus, cytosolic pH and H2O2 levels may play an important role in the modulation of the cytoplasmic free calcium concentration through BCC1.

Calcium↗
PubMed1996

Identification of a high affinity divalent cation binding site near the entrance of the NMDA receptor channel.

Single channel currents from recombinant N-methyl-D-aspartate (NMDA) receptors having an N-to-Q mutation in M2 reveal a divalent cation binding site that is near the entrance of the pore (approximately 0.2 through the electric field). Ca2+ rapidly binds to this site and readily permeates the channel, while Mg2+ binds more slowly and does not permeate as readily. In wild-type receptors, Mg2+ also blocks the current by occupying a site that is approximately 0.6 through the field. When the more external site is occupied by Ca2+, the conductance of the pore to NA+ is reduced but not abolished, perhaps by an electrostatic blocking mechanism. The site serves to enrich the fraction of NMDA receptor current carried by CA2+.

Animals↗
PubMed2002

The use of elevated divalent cation solutions to isolate monosynaptic components of sensorimotor connections in Aplysia.

A commonly used method to remove polysynaptic components of test PSPs is to elevate action potential threshold of interneurons with high extracellular concentrations of divalent cations ('Hi-Di'). Extrapolation to normal conditions requires that Hi-Di have negligible effects on synaptic transmission. We examined effects of Hi-Di on EPSPs from sensory neurons (SNs) onto motor neurons (MNs) of Aplysia in the pleural-pedal and abdominal ganglia, and in dissociated cell culture. In ganglia, standard Hi-Di solutions eliminated spontaneous input from interneurons as well as polysynaptic components of PSPs evoked by single action potentials in single SNs, but failed to block polysynaptic PSPs evoked by nerve stimulation. Hi-Di solutions had no effect on activity-dependent synaptic depression or posttetanic potentiation, or facilitation by serotonin (5-HT). Unexpectedly, standard Hi-Di solutions substantially reduced sensorimotor EPSPs in all preparations, whereas a solution containing 2.2x[Ca(2+)] and 2x[Mg(2+)] blocked the polysynaptic component of EPSPs without obvious changes to the monosynaptic component. In contrast to previous observations in Aplysia, and to predictions of the (J. Physiol. 193 (1967) 419) model, tripling the normal extracellular concentrations of Ca(2+) and Mg(2+) failed to increase sensorimotor EPSPs. Depression of EPSPs by these Hi-Di solutions may result from reduced spike invasion into presynaptic terminals.

Animals↗
PubMed2001

Mutational analysis of baculovirus capping enzyme Lef4 delineates an autonomous triphosphatase domain and structural determinants of divalent cation specificity.

The 464-amino acid baculovirus Lef4 protein is a bifunctional mRNA capping enzyme with triphosphatase and guanylyltransferase activities. The hydrolysis of 5'-triphosphate RNA and free NTPs by Lef4 is dependent on a divalent cation cofactor. RNA triphosphatase activity is optimal at pH 7.5 with either magnesium or manganese, yet NTP hydrolysis at neutral pH is activated only by manganese or cobalt. Here we show that Lef4 possesses an intrinsic magnesium-dependent ATPase with a distinctive alkaline pH optimum and a high K(m) for ATP (4 mm). Lef4 contains two conserved sequences, motif A ((8)IEKEISY(14)) and motif C ((180)LEYEF(184)), which define the fungal/viral/protozoal family of metal-dependent RNA triphosphatases. We find by mutational analysis that Glu(9), Glu(11), Glu(181), and Glu(183) are essential for phosphohydrolase chemistry and likely comprise the metal-binding site of Lef4. Conservative mutations E9D and E183D abrogate the magnesium-dependent triphosphatase activities of Lef4 and transform it into a strictly manganese-dependent RNA triphosphatase. Limited proteolysis of Lef4 and ensuing COOH-terminal deletion analysis revealed that the NH(2)-terminal 236-amino acid segment of Lef4 constitutes an autonomous triphosphatase catalytic domain.

Acid Anhydride Hydrolases↗
PubMed1984

Effects of external calcium reduction on biphasic potassium contractures and action of divalent cations on the calcium reduction in frog single twitch muscle fibers.

The effects of external Ca2+ reduction on the biphasic potassium (K) contractures and the action of divalent cations under conditions of the Ca2+ reduction were examined in detail, using frog single twitch muscle fibers. The peak tension of the initial component of 80 mM K+ contractures was greatly potentiated by exposing the fiber to low Ca2+ solution for 30 sec, and the degree of this potentiation was decreased with increasing the exposing time. In contrast, the peak tension of the secondary component was rapidly inhibited by Ca2+ reduction. The potentiation of the initial component was removed by 3 mM Mg2+ or 0.5 mM Ni2+. The inhibition of the secondary component, especially the shortening of its time course, was reversed partially by 3 mM Mg2+ and almost completely by 0.5 mM Ni2+. The difference between the inhibitory effect of 10 mM Mg2+ or 1-3 mM Ni2+ on the initial component and that on the secondary component was also demonstrated. The tension development of the secondary component was completely inhibited by external Ca2+ reduction for 20 min, but it was observed in the presence of 3 mM Mg2+, although its time course was shorter. These results indicate that the actions of Mg2+ and Ni2+ on the initial component differ from those on the secondary component and suggest the possible mechanisms of the actions of these divalent cations on the biphasic K contractures.

Animals↗
PubMed2001

Effects of divalent cations on voltage-gated Ca2+ channels and depolarization-induced [Ca2+], transients of freshly isolated pyramidal cells of the rat dorsal cochlear nucleus.

The effects of divalent cations on voltage-activated Ca2+ channels and depolarization-evoked cytoplasmic [Ca2+] elevations were studied in pyramidal neurones isolated from the dorsal cochlear nucleus of the rat. Ca2+ currents were recorded using the whole-cell configuration of the patch-clamp technique. 10 micromol x l(-1) Cd2+ exerted a greater blocking effect on the high-voltage activated (HVA) currents than on the low-voltage activated (LVA) ones (decrease to 26.6+/-2.5% and to 87.8+/-2.1%, respectively). The blocking effect of 200 micromol x l(-1) Cd2+ was more pronounced and the difference between the effect on the HVA and LVA currents became smaller (decrease to 11.7+/-2.1% and to 32.4+/-2.7%, respectively). 200 micromol x l(-1) Ni2+ reduced the LVA component more effectively (to 77.6+/-5.4%) than the HVA one (to 86.9+/-2.6%). Cytoplasmic [Ca2+] changes were measured applying a fluorimetric technique (Fura-2). 10 micromol x l(-1) Cd2+ decreased the peak values of 50 mmol x l(-1) K+ depolarization-induced [Ca2]+i transients to 30.4+/-1.4% while 200 micromol x l(-1) Cd2+ caused a drop to 2.5+/-0.2%. 200 micromol x l(-1) Ni2+ decreased the peak of the transients to 69.6+/-2.9%. Comparison of the blocking effects of divalent cations on Ca2+ currents and [Ca2+]i transients supports further the conclusion that the depolarization-induced [Ca2+]i changes are produced mainly by the activation of the HVA Ca2+ channels.

Animals↗
PubMed1992

Pseudomonas aeruginosa acid phosphatase. Activation by divalent cations and inhibition by aluminium ion.

In Pseudomonas aeruginosa, the effect of different cations on the acid phosphatase activity was studied in order to acquire more information related to a previously proposed mechanism, involving the coordinated action of this enzyme with phospholipase C. Although the natural substrate of this enzyme is phosphorylcholine, in order to avoid the possible interaction of its positive charge and those of the different cations with the enzyme molecule, the artificial substrate p-nitrophenylphosphate was utilized. Kinetic studies of the activation of acid phosphatase (phosphorylcholine phosphatase) mediated by divalent cations Mg2+, Zn2+ and Cu2+ revealed that all these ions bind to the enzyme in a compulsory order (ordered bireactant system). The Km values obtained for p-NPP in the presence of Mg2+, Zn2+ and Cu2+ were 1.4 mM, 1.0 mM and 3.5 mM, respectively. The KA values for the same ions were 1.25 mM, 0.05 mM and 0.03 mM, respectively. The Vmax obtained in the presence of Cu2+ was about twofold higher than that obtained in the presence of Mg2+ or Zn2+. The inhibition observed with Al3+ seems to be a multi-site inhibition. The K'app and n values, from the Hill plot, were about 0.25 mM and 4.0 mM, respectively, which were independent of the metal ion utilized as activator. It is proposed that the acid phosphatase may exert its action under physiological conditions, depending on the availability of either one of these metal ions.

Acid Phosphatase↗
PubMed1975

Effects of divalent cations and of catecholamines on the late response of the superior cervical ganglion.

The characteristics of the late response of the superior cervical ganglion of dogs were studied by close-arterial injection of catecholamines and divalent cations to the ganglion. 2. Dopamine, noradrenaline and adrenaline inhibit the late response as well as ganglionic activity induced by other means. The effect of dopamine is brief but that of adrenaline is prolonged. 3. Cd2+, Co2+, Ni2+, Zn2+, Hg2+ and Fe2+ markedly potentiate the late response, whereas Mn2+, Ca2+ and Mg2+ inhibit it. 4. may potentiate ganglionic activity triggered by other ganglionic stimulants. The Cd-augmented activity may be blocked by a ganglion-blocker which is specific to the stimulant. 5. CdCl2 may exhibit a direct ganglion-stimulating action on a ganglion which shows prominent late responses and has been conditioned by tetanic preganglionic stimulation. 6. CdCl2 and MnCl2 may inhibit ganglionic transmission by suppressing acetylcholine release from presynaptic nerve terminals. 7. It is concluded that the late response represents the late discharges of ganglion cells, which are very sensitive to inhibition by CaCl2 and MnCl2 and may be potentiated by CdCl2.

Animals↗
PubMed1987

Permeation and block of N-methyl-D-aspartic acid receptor channels by divalent cations in mouse cultured central neurones.

1. Spinal cord and hippocampal neurones in cell culture were voltage clamped using the tight-seal, whole-cell recording technique. The concentration of sodium and a series of divalent cations in the extracellular media was varied to study permeation through excitatory amino acid receptor channels activated by the selective agonists N-methyl-D-aspartic acid (NMDA), kainic acid and quisqualic acid. 2. On raising the extracellular calcium concentration, with [Na+]o held constant at 105 mM, the reversal potential of responses to NMDA shifted in the depolarizing direction. This shift was adequately described by the extended constant-field equation over the range 0.3-50 mM-calcium. Using ionic activity coefficients we calculate a value of PCa/PNa = 10.6. Under the same experimental conditions the reversal potential of responses to kainic and quisqualic acids was much less affected by raising the calcium concentration, such that PCa/PNa = 0.15. A depolarizing shift of the NMDA reversal potential was also recorded during application of 20 mM-barium, strontium or manganese, suggesting permeation of these ions. The permeability sequence was Ca2+ greater than Ba2+ greater than Sr2+ much greater than Mn2+. No depolarizing shift of the NMDA reversal potential occurred during application of 20 mM-cobalt, magnesium or nickel. 3. In experiments in which the extracellular Na+ concentration was varied the extended constant-field equation was adequate in predicting shifts of the NMDA reversal potential recorded on varying [Na+]o over the range 50-150 mM, but failed to accurately predict the reversal potential of responses to NMDA with 10 mM-[Ca2+]o and only 10 or 20 mM-[Na+]o. These results imply an apparent increase in PCa/PNa on lowering [Na+]o and may result from interaction of permeant ions within the channel. 4. Barium and to a lesser extent calcium, but not strontium (all 20 mM), reduced the slope conductance of responses to NMDA recorded within +/- 15 mV of the reversal potential; over this limited range of membrane potential the current-voltage relationship remained linear in the presence of each of these ions. In contrast manganese produced a strong, voltage-dependent block of responses to NMDA, similar to that produced by magnesium, such that even close to the reversal potential the NMDA current-voltage relationship was highly non-linear. Thus manganese both permeates and blocks the NMDA receptor channel. 5. Raising the extracellular calcium concentration, from 0.1 to 5 mM, had two effects on the conductance mechanism activated by NMDA.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗