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At least 1,189 records · Page 66Linked to original sources
PubMed1999

Involvement of inositol 1,4,5-trisphosphate-regulated stores of intracellular calcium in calcium dysregulation and neuron cell death caused by HIV-1 protein tat.

HIV-1 infection commonly leads to neuronal cell death and a debilitating syndrome known as AIDS-related dementia complex. The HIV-1 protein Tat is neurotoxic, and because cell survival is affected by the intracellular calcium concentration ([Ca2+]i), we determined mechanisms by which Tat increased [Ca2+]i and the involvement of these mechanisms in Tat-induced neurotoxicity. Tat increased [Ca2+]i dose-dependently in cultured human fetal neurons and astrocytes. In neurons, but not astrocytes, we observed biphasic increases of [Ca2+]i. Initial transient increases were larger in astrocytes than in neurons and in both cell types were significantly attenuated by antagonists of inositol 1,4,5-trisphosphate (IP3)-mediated intracellular calcium release [8-(diethylamino)octyl-3,4,5-trimethoxybenzoate HCI (TMB-8) and xestospongin], an inhibitor of receptor-Gi protein coupling (pertussis toxin), and a phospholipase C inhibitor (neomycin). Tat significantly increased levels of IP3 threefold. Secondary increases of neuronal [Ca2+]i in neurons were delayed and progressive as a result of excessive calcium influx and were inhibited by the glutamate receptor antagonists ketamine, MK-801, (+/-)-2-amino-5-phosphonopentanoic acid, and 6,7-dinitroquinoxaline-2,3-dione. Secondary increases of [Ca2+]i did not occur when initial increases of [Ca2+]i were prevented with TMB-8, xestospongin, pertussis toxin, or neomycin, and these inhibitors as well as thapsigargin inhibited Tat-induced neurotoxicity. These results suggest that Tat, via pertussis toxin-sensitive phospholipase C activity, induces calcium release from IP3-sensitive intracellular stores, which leads to glutamate receptor-mediated calcium influx, dysregulation of [Ca2+]i, and Tat-induced neurotoxicity.

2-Amino-5-phosphonovalerate↗
PubMed2005

Anti-platelet aggregating and anti-oxidative activities of 11-O-(4'-O-methylgalloyl)-bergenin, a new compound isolated from Crassula cv. 'Himaturi'.

A new compound, 11- O-(4'- O-methylgalloyl)-bergenin was isolated from the MeOH extract of Crassula cv. 'Himaturi'. The structure of the compound was determined on the basis of chemical and spectroscopic data. It inhibited arachidonic acid-induced platelet aggregation more efficiently than acetylsalicylic acid and showed an anti-oxidative effect (EC (50) = 23.9 microM) equivalent to that of L-ascorbic acid or quercetin.

Antioxidants↗
PubMed1991

Bradykinin induces elevations of cytosolic calcium through mobilisation of intracellular and extracellular pools in bovine aortic endothelial cells.

1. In the presence of 1.8 mM extracellular calcium, bradykinin (0.3 nM-100 nM) induced a biphasic elevation of intracellular calcium ([Ca2+]i) in bovine aortic endothelial cells, consisting of an initial, large transient component followed by a lower sustained component. 2. When endothelial cells were bathed in nominally calcium-free solution containing 0.5 mM EGTA, bradykinin induced only a transient elevation of [Ca2+]i: the magnitude of this was significantly smaller than that obtained in the presence of extracellular calcium and the sustained phase was abolished. In the continued presence of bradykinin, re-addition of extracellular calcium to achieve a level of around 1.8 mM resulted in the induction of a biphasic elevation of [Ca2+]i consisting of a large initial component followed by a lower sustained component. 3. In the presence of 1.8 mM extracellular calcium, caffeine (5 mM) induced a small elevation of [Ca2+]i. When endothelial cells were bathed in nominally calcium-free solution containing 0.5 mM EGTA, the caffeine-induced elevation of [Ca2+]i was almost completely abolished. 4. In the presence of 1.8 mM extracellular calcium, treatment of endothelial cells with the calcium influx blocker, nickel chloride (4 mM), had no effect on resting [Ca2+]i or on the magnitude of the bradykinin-induced initial transient elevation of [Ca2+]i but abolished the sustained component. 5. In the presence of 1 mM extracellular calcium, treatment with the calcium chelator EGTA (2 mM; 1 min) had no effect on resting [Ca2+]i but the magnitude of the bradykinin-induced initial transient elevation of [Ca2+]i was significantly reduced. Increasing the exposure time or concentration of EGTA resulted in no further reduction in the magnitude of the bradykinin-induced transient component. 6. Treatment of endothelial cells with the putative inhibitor of intracellular calcium release, 3,4,5-trimethoxybenzoic acid 84diethylamino)octyl ester (TMB-8, 0.1 mM) increased resting [Ca21]i slightly but had no effect on the magnitude of the bradykinin-stimulated elevation of [Ca22ji. 7. These findings suggest that, in bovine aortic endothelial cells, the bradykinin-induced initial transient elevation of [Ca21]i is completely dependent upon release of calcium from intracellular stores and the sustained component is due to calcium influx. They further suggest the possible existence of two intracellular calcium pools, one which is rapidly depleted in the absence of extracellular calcium and a second which is resistant to such depletion.

Animals↗
PubMed1991

Low doses of ethanol have Ca2+ ionophore-like effects on apical membrane potential of in vitro Necturus antrum.

The effects of low doses of luminal ethanol on the amiloride-sensitive apical membrane potential of Necturus antral mucosa were studied using conventional microelectrode techniques. Luminal ethanol (0.250-4.0% vol/vol) caused a dose-dependent hyperpolarization of the apical membrane potential (Vmc), an increase in transepithelial resistance (Rt) and resistance ratio (Ra/Rb), and a decrease in transepithelial potential (Vms). Luminal amiloride (100 microM) to 4% ethanol-treated antra did not cause any additional hyperpolarization of Vmc. Compared with luminal 2% ethanol-Ringer, an equivalent osmotic mannitol solution depolarized Vmc and basolateral potential (Vcs), decreased Rt and Ra/Rb, and increased Vms. A single dose of 0.50% ethanol attenuated the effects of a second 2% ethanol exposure on Vmc. No change in periodic acid-Schiff (PAS)-positive mucous granule content could be found between control and 2% ethanol-treated antra. The Ca2+ ionophores A23187 or ionomycin (0.25-5.0 microM) dose dependently hyperpolarized the Vmc and Vcs, increased Rt and Ra/Rb, and decreased Vms. Luminal Ca(2+)-free Ringer had no effect on luminal 2.00% ethanol-induced changes in membrane potentials or resistances. Pretreatment with BAPTA blocked by approximately 70 and 55% the Vmc hyperpolarization of 2 and 4% ethanol, respectively. Pretreatment with ruthenium red (10-50 microM) also dose dependently reduced the 2% ethanol-induced changes in Vmc. The data indicate that 1) low doses of luminal ethanol and Ca2+ ionophores have similar effects on Necturus gastric antral membrane potentials and resistances, 2) ethanol-induced hyperpolarizations of the Vmc are partially mediated through an alteration in intracellular Ca2+, and 3) low doses of luminal ethanol do not cause the release of antral epithelial mucous granules at the time when significant changes are occurring in the Vmc.

Animals↗
PubMed1993

Carbachol-induced potassium release in rat parotid acini: comparison of the roles of cytosolic Ca2+ and protein kinase C.

Carbachol (CCh) stimulated K+ release from rat parotid acini. Treatment with the intracellular Ca2+ antagonist 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) or the intracellular Ca2+ chelator 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) strongly suppressed the CCh-induced K+ release. Combined addition of the Ca2+ ionophore ionomycin and the microsomal Ca(2+)-ATPase inhibitor thapsigargin caused a rapid increase in cytosolic Ca2+ concentration ([Ca2+]i) and resulted in a marked release of K+. In the absence of extracellular Ca2+, CCh or a combination of ionomycin and thapsigargin caused a transient release of K+ which correlated well with the transient change in [Ca2+]i. On the other hand, phorbol 12-myristate 13-acetate (PMA) did not potentiate the CCh-induced K+ release, although the CCh-induced amylase release was significantly enhanced in the presence of PMA. Staurosporine, a protein kinase C-inhibitor, did not inhibit the CCh-induced K+ release, which was in contrast with its inhibitory effect on amylase release. These results suggest that the K+ release from rat parotid acini induced by CCh stimulation is mediated by a rapid increase in [Ca2+]i but is not associated with activation of protein kinase C. This signal pathway is different from that for amylase release where activation of protein kinase C plays an important role.

Alkaloids↗
PubMed1999

Influence of inhibitors on increase in intracellular free calcium and proliferation induced by platelet-activating factor in bovine oviductal cells.

Oviductal endosalpingeal cells were isolated mechanically from heifers and cultured until there was 100% confluency. The cells were loaded with the Ca(2+)-sensitive fluorochrome, fura-2/acetoxymethylester, and cytosolic free calcium ([Ca2+]i) was monitored by spectrofluorimetry. Platelet-activating factor, at a concentration of 30 nmol l-1, induced an intracellular Ca2+ increase in cultured bovine oviductal cells, mainly via influx from the extracellular space. In fura-2-loaded oviductal cells, different Ca2+ channel blockers were investigated to characterize the pathways responsible for the Ca2+ influx. The negative effects of Ni(2+)-, La(3+)-activated K+ channel blockers, such as apamin and charybdotoxin, and Ca2+ channel blockers, such as dotarizine, on the platelet-activating factor-induced [Ca2+]i increase indicate the minor participation of the voltage-gated Ca2+ channels. TMB-8 and flufenamic acid blocked the platelet-activating factor-induced Ca2+ increase directly on non-selective cationic channels or acted via a Ca2+ release-triggered Ca2+ influx. Platelet-activating factor, at concentrations of 1.25 mumol l-1 and 2.5 mumol l-1, significantly stimulated the proliferation and depolarization of oviductal cells, but 10 mumol l-1 significantly decreased both parameters and exerted a cytotoxic effect on cells. After incubation with TMB-8 or flufenamic acid, the cell proliferation was inhibited in a concentration-dependent manner, with IC50 values of 26.57 mumol l-1 and 95.29 mumol l-1, respectively. The depolarization was significantly inhibited at 50 mumol l-1 for both TMB-8 and flufenamic acid. The results of the present study may contribute to further understanding of the mechanism behind the actions of platelet-activating factor on oviductal cells.

Analysis of Variance↗
PubMed1979

Oxidative and demethylating activity of multiple forms of laccase from Pholiota mutabilis.

1. The inducible and constitutive forms of laccase from the fungus Pholiota mutabilis show both the oxidative and demethylating activity, which proves the bifunctional character of the enzyme. 2. The oxidative/demethylating activity ratio of the forms induced either with ferulic or syringic acid is different from that shown by the constitutive form. 3. Splitting of one methoxyl group from the methoxyphenol substrate is associated with the release of one molecule of methanol.

Agaricales↗
PubMed1993

TMB-8 and thapsigargin modulate purine release from dissociated primary cultures of rat brain astrocytes.

In our previous studies, the evoked purine outflow from rat brain cultured astrocytes was reported to be Na+ independent and K+ and [Ca2+]e partially dependent. Thus, the eventual [Ca2+]i influence on purine astrocyte release was investigated in an attempt to better characterize the ionic requirements of this mechanism in cells which serve many complex and still partly unknown functions within the CNS. TMB-8 and Thapsigargin (drugs described as able to inhibit and increase the ion efflux from its internal stores respectively) and BAPTA/AM (able to chelate the cytoplasmic free Ca2+), were used. TMB-8 and BAPTA/AM decreased, whereas Thapsigargin enhanced glial purine outflow. These findings suggest a significant [Ca2+]i dependence of the electrically evoked purine efflux from cultured astrocytes even though further investigations using fluorescent probes are needed.

Adenosine↗
PubMed2000

Analysis of oak tannins by liquid chromatography-electrospray ionisation mass spectrometry.

Extractable tannins were analysed by liquid chromatography-electrospray ionisation mass spectrometry in two oak species, North American white oak (Quercus alba) and European red oak (Quercus robur). They mainly included various glucose gallic and ellagic acid esters. The structures were partially determined, and they included grandinin/roburin E, castalagin/vescalagin, gallic acid, valoneic acid bilactone, monogalloyl glucose, digalloyl glucose, trigalloyl glucose, ellagic acid rhamnose, quercitrin and ellagic acid.

Chromatography, Liquid↗