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Results for “Ca(2+)”

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At least 19 recordsLinked to original sources

PubMed2004

Module-based assembly of copper(II) chloranilate compounds: syntheses, crystal structures, and magnetic properties of [[Cu(2)(CA)(terpy)(2)][Cu(CA)(2)]](n)() and [[Cu(2)(CA)(terpy)(2)(dmso)(2)][Cu(CA)(2)(dmso)(2)](EtOH)](n)(H(2)CA = chloranilic acid, terpy = 2,2':6',2' '-terpyridine, dmso = dimethyl sulfoxide).

Two new copper(II) compounds of chloranilate and 2,2':6',2' '-terpyridine have been synthesized, and the structures have been solved by the single-crystal X-ray diffraction method. The crystal structure of [[Cu(2)(CA)(terpy)(2)][Cu(CA)(2)]](n)(1), where H(2)CA = chloranilic acid and terpy = 2,2':6',2' '-terpyridine, consists of two modules, the dimer unit [Cu(2)(CA)(terpy)(2)](2+) and the anionic mononuclear unit [Cu(CA)(2)](2)(-), forming an alternated chain. The chain is stabilized by semicoordinating and additional but efficient secondary bonding interactions. The crystal structure of [[Cu(2)(CA)(terpy)(2)(dmso)(2)][Cu(CA)(2)(dmso)(2)](EtOH)](n)(2), where dmso = dimethyl sulfoxide, consists of solvent molecules and two discrete modules, the dimer unit [Cu(2)(CA)(terpy)(2)(dmso)(2)](2+) and the anionic mononuclear unit [Cu(CA)(2)(dmso)(2)](2)(-). The dimer units form a layer by secondary bonding interactions, and the monomer units and ethanol molecules are introduced between the layers. The magnetic properties of 1 and 2 have been investigated in the temperature range 2.0-300 K. A weak ferromagnetic interaction was observed in 1, J(a) = 2.36 cm(-)(1) and zJ(b) = -0.68 cm(-)(1) while no exchange coupling was observed in 2.

Journal Article↗

PubMed2001

Surface Complexation Modeling of K(+), NO(3)(-), SO(4)(2-), Ca(2+), F(-), Co(2+), and Cr(3+) Ion Adsorption on Silica Gel.

Surface complex formation of K(+), NO(3)(-), SO(4)(2-), Ca(2+), F(-), Co(2+), and Cr(3+) ions was determined on the surface of silica gel. Experimental data obtained by acid-base titration of suspensions were interpreted in terms of the triple-layer model. The value of the deprotonation constant of surface OH could be determined precisely but the protonation constant was rather uncertain. The logarithms of ion pair formation constants for K(+), NO(3)(-), Ca(2+), and SO(4)(2-) adsorbed in the beta-plane are log K(ipM,X) approximately 0, therefore these species can be considered inert ions in the investigated pH range. F(-), Co(2+), and Cr(3+) ions were found to be strongly sorbed in the o-plane. In order to provide a good fit and to obtain parameters independent of their initial values, all possible equilibrium must be accounted for in the models. Copyright 2001 Academic Press.

Journal Article↗

PubMed1996

Okadaic acid as a probe for regulation in vitro of Mg(2+), Ca(2+)-ATPase activity in rat cortical and cerebellar synaptosomal membranes.

The in vitro effect of okadaic acid on basal phorbol 12-myristate 13-acetate (PMA)-, and cyclic adenosine monophosphate (cAMP)-stimulated Mg(2+)-dependent Ca(2+)-adenosine triphosphatase (ATPase) activity in synaptosomal membranes isolated from rat brain cortex and cerebellum was investigated. The basal activity was enhanced by okadaic acid in both examined regions. This inhibitor differed in the regulation of Mg2+, Ca(2+)-ATPase activity in PMA- and cAMP-incubated membranes. Stimulation by calmodulin (CaM) of basal Mg2+, Ca(2+)-ATPase activity declined in cortex and cerebellum after treatment with okadaic acid. The presence of PMA or cAMP decreases the stimulatory effect of CaM. These results suggest that Mg2+, Ca(2+)-ATPase activity in the rat-brain synaptosomal membrane may be regulated in vitro by dephosphorylation processes.

Animals↗

PubMed2002

Electronic structure of the trilayer cuprate superconductor Bi(2)Sr(2)Ca(2)Cu(3)O(10+delta).

The low-energy electronic structure of the nearly optimally doped trilayer cuprate superconductor Bi(2)Sr(2)Ca(2)Cu(3)O(10+delta) is investigated by angle-resolved photoemission spectroscopy. The normal state quasiparticle dispersion and Fermi surface and the superconducting d-wave gap and coherence peak are observed and compared with those of single- and bilayer systems. We find that both the superconducting gap magnitude and the relative coherence-peak intensity scale linearly with T(c) for various optimally doped materials.

Journal Article↗

PubMed2001

PGE(2), Ca(2+), and cAMP mediate ATP activation of Cl(-) channels in pigmented ciliary epithelial cells.

Purines regulate intraocular pressure. Adenosine activates Cl(-) channels of nonpigmented ciliary epithelial cells facing the aqueous humor, enhancing secretion. Tamoxifen and ATP synergistically activate Cl(-) channels of pigmented ciliary epithelial (PE) cells facing the stroma, potentially reducing net secretion. The actions of nucleotides alone on Cl(-) channel activity of bovine PE cells were studied by electronic cell sorting, patch clamping, and luciferin/luciferase ATP assay. Cl(-) channels were activated by ATP > UTP, ADP, and UDP, but not by 2-methylthio-ATP, all at 100 microM. UTP triggered ATP release. The second messengers Ca(2+), prostaglandin (PG)E(2), and cAMP activated Cl(-) channels without enhancing effects of 100 microM ATP. Buffering intracellular Ca(2+) activity with 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'- tetraacetic acid or blocking PGE(2) formation with indomethacin inhibited ATP-triggered channel activation. The Rp stereoisomer of 8-bromoadenosine 3',5'-cyclic monophosphothioate inhibited protein kinase A activity but mimicked 8-bromoadenosine 3',5'-cyclic monophosphate. We conclude that nucleotides can act at >1 P2Y receptor to trigger a sequential cascade involving Ca(2+), PGE(2), and cAMP. cAMP acts directly on Cl(-) channels of PE cells, increasing stromal release and potentially reducing net aqueous humor formation and intraocular pressure.

Adenosine Triphosphate↗

PubMed2001

Adrenergic stimulation of rat resistance arteries affects Ca(2+) sparks, Ca(2+) waves, and Ca(2+) oscillations.

Confocal laser scanning microscopy and fluo 4 were used to visualize local and whole cell Ca(2+) transients within individual smooth muscle cells (SMC) of intact, pressurized rat mesenteric small arteries during activation of alpha1-adrenoceptors. A method was developed to record the Ca(2+) transients within individual SMC during the changes in arterial diameter. Three distinct types of "Ca(2+) signals" were influenced by adrenergic activation (agonist: phenylephrine). First, asynchronous Ca(2+) transients were elicited by low levels of adrenergic stimulation. These propagated from a point of origin and then filled the cell. Second, synchronous, spatially uniform Ca(2+) transients, not reported previously, occurred at higher levels of adrenergic stimulation and continued for long periods during oscillatory vasomotion. Finally, Ca(2+) sparks slowly decreased in frequency of occurrence during exposure to adrenergic agonists. Thus adrenergic activation causes a decrease in the frequency of Ca(2+) sparks and an increase in the frequency of asynchronous wavelike Ca(2+) transients, both of which should tend to decrease arterial diameter. Oscillatory vasomotion is associated with spatially uniform synchronous oscillations of cellular [Ca(2+)] and may have a different mechanism than the asynchronous, propagating Ca(2+) transients.

Animals↗

PubMed2001

Mitochondrial Ca(2+)-induced Ca(2+) release mediated by the Ca(2+) uniporter.

We have reported that a population of chromaffin cell mitochondria takes up large amounts of Ca(2+) during cell stimulation. The present study focuses on the pathways for mitochondrial Ca(2+) efflux. Treatment with protonophores before cell stimulation abolished mitochondrial Ca(2+) uptake and increased the cytosolic [Ca(2+)] ([Ca(2+)](c)) peak induced by the stimulus. Instead, when protonophores were added after cell stimulation, they did not modify [Ca(2+)](c) kinetics and inhibited Ca(2+) release from Ca(2+)-loaded mitochondria. This effect was due to inhibition of mitochondrial Na(+)/Ca(2+) exchange, because blocking this system with CGP37157 produced no further effect. Increasing extramitochondrial [Ca(2+)](c) triggered fast Ca(2+) release from these depolarized Ca(2+)-loaded mitochondria, both in intact or permeabilized cells. These effects of protonophores were mimicked by valinomycin, but not by nigericin. The observed mitochondrial Ca(2+)-induced Ca(2+) release response was insensitive to cyclosporin A and CGP37157 but fully blocked by ruthenium red, suggesting that it may be mediated by reversal of the Ca(2+) uniporter. This novel kind of mitochondrial Ca(2+)-induced Ca(2+) release might contribute to Ca(2+) clearance from mitochondria that become depolarized during Ca(2+) overload.

Aequorin↗

PubMed2000

Role of Mg(2+) in Ca(2+)-induced Ca(2+) release through ryanodine receptors of frog skeletal muscle: modulations by adenine nucleotides and caffeine.

Mg(2+) serves as a competitive antagonist against Ca(2+) in the high-affinity Ca(2+) activation site (A-site) and as an agonist of Ca(2+) in the low-affinity Ca(2+) inactivation site (I-site) of the ryanodine receptor (RyR), which mediates Ca(2+)-induced Ca(2+) release (CICR). This paper presents the quantitative determination of the affinities for Ca(2+) and Mg(2+) of A- and I-sites of RyR in frog skeletal muscles by measuring [(3)H]ryanodine binding to purified alpha- and beta-RyRs and CICR activity in skinned fibers. There was only a minor difference in affinity at most between alpha- and beta-RyRs. The A-site favored Ca(2+) 20- to 30-fold over Mg(2+), whereas the I-site was nonselective between the two cations. The RyR in situ showed fivefold higher affinities for Ca(2+) and Mg(2+) of both sites than the purified alpha- and beta-RyRs with unchanged cation selectivity. Adenine nucleotides, whose stimulating effect was found to be indistinguishable between free and complexed forms, did not alter the affinities for cations in either site, except for the increased maximum activity of RyR. Caffeine increased not only the affinity of the A-site for Ca(2+) alone, but also the maximum activity of RyR with otherwise minor changes. The results presented here suggest that the rate of CICR in frog skeletal muscles appears to be too low to explain the physiological Ca(2+) release, even though Mg(2+) inhibition disappears.

Adenine Nucleotides↗

PubMed2000

Requirement of ryanodine receptor subtypes 1 and 2 for Ca(2+)-induced Ca(2+) release in vascular myocytes.

While the roles of subtypes 1 and 2 of the ryanodine receptors (RYRs) have been studied in cellular systems expressing specifically one or the other of these subtypes (i.e. skeletal and cardiac muscle), the function of these receptors has not been evaluated in smooth muscles. We have previously reported RYR-mediated elementary (Ca(2+) sparks) and global Ca(2+) responses in rat portal vein myocytes. Here, we investigated the respective roles of all three RYR subtypes expressed in these cells as revealed by reverse transcriptase-polymerase chain reaction. Antisense oligonucleotides targeting each one of the three RYR subtypes were shown to specifically inhibit the expression of the corresponding mRNA and protein without affecting the other RYR subtypes. Confocal Ca(2+) measurements revealed that depolarization-induced Ca(2+) sparks and global Ca(2+) responses were blocked when either RYR1 or RYR2 expression was suppressed. Caffeine-induced Ca(2+) responses were partly inhibited by the same antisense oligonucleotides. Neither the corresponding scrambled oligonucleotides nor the antisense oligonucleotides targeting RYR3 affected depolarization- or caffeine-induced Ca(2+) responses. Our results show that, in vascular myocytes, the two RYR1 and RYR2 subtypes are required for Ca(2+) release during Ca(2+) sparks and global Ca(2+) responses, evoked by activation of voltage-gated Ca(2+) channels.

Animals↗

PubMed2005

'Ca(2+)-induced Ca(2+) entry' or how the L-type Ca(2+) channel remodels its own signalling pathway in cardiac cells.

The adjustment of Ca(2+) entry in cardiac cells is critical to the generation of the force necessary for the myocardium to meet the physiological needs of the body. In this review, we present the concept that Ca(2+) can promote its own entry through Ca(2+) channels by different mechanisms. We refer to it under the general term of 'Ca(2+)-induced Ca(2+) entry' (CICE). We review short-term mechanisms (usually termed facilitation) that involve a stimulating effect of Ca(2+) on the L-type Ca(2+) current (I(Ca-L)) amplitude (positive staircase) or a lessening of Ca(2+)-dependent inactivation of I(Ca-L). This latter effect is related to the amount of Ca(2+) released by ryanodine receptors (RyR2) of the sarcoplasmic reticulum (SR). Both effects are involved in the control of action potential (AP) duration. We also describe a long-term mechanism based on Ca(2+)-dependent down-regulation of the Kv4.2 gene controlling functional expression of the repolarizing transient outward K(+) current (I(to)) and, thereby, AP duration. This mechanism, which might occur very early during the onset of hypertrophy, enhances Ca(2+) entry by maintaining Ca(2+) channel activation during prolonged AP. Both Ca(2+)-dependent facilitation and Ca(2+)-dependent down-regulation of I(to) expression favour AP prolongation and, thereby, promote sustained voltage-gated Ca(2+) entry used to enhance excitation-contraction (EC) coupling (with no change in the density of Ca(2+) channels per se). These self-maintaining mechanisms of Ca(2+) entry have significant functions in remodelling Ca(2+) signalling during the cardiac AP. They might support a prominent role of Ca(2+) channels in the establishment and progression of abnormal Ca(2+) signalling during cardiac hypertrophy and congestive heart failure.

Animals↗

PubMed2003

Ca(2+)-induced Ca(2+) release in the pancreatic beta-cell: direct evidence of endoplasmic reticulum Ca(2+) release.

The role of the Ca(2+)-induced Ca(2+) release channel (ryanodine receptor) in MIN6 pancreatic beta-cells was investigated. An endoplasmic reticulum (ER)-targeted "cameleon" was used to report lumenal free Ca(2+). Depolarization of MIN6 cells with KCl led to release of Ca(2+) from the ER. This ER Ca(2+) release was mimicked by treatment with the ryanodine receptor agonists caffeine and 4-chloro-m-cresol, reversed by voltage-gated Ca(2+) channel antagonists and blocked by treatment with antagonistic concentrations of ryanodine. The depolarization-induced rise in cytoplasmic Ca(2+) was also inhibited by ryanodine, which did not alter voltage-gated Ca(2+) channel activation. Both ER and cytoplasmic Ca(2+) changes induced by depolarization occurred in a dose-dependent manner. Glucose caused a delayed rise in cytoplasmic Ca(2+) but no detectable change in ER Ca(2+). Carbamyl choline caused ER Ca(2+) release, a response that was not altered by ryanodine. Taken together, these results provide strong evidence that Ca(2+)-induced Ca(2+) release augments cytoplasmic Ca(2+) signals in pancreatic beta-cells.

Caffeine↗

PubMed2000