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2001
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vol. 48
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issue 1
157-161
EN
The effects of various concentrations of thapsigargin, a specific inhibitor of Ca2+-ATPase in the endoplasmic reticulum (ER) membrane, on calcium homeostasis in lymphoidal T cells (Jurkat) were investigated. Preincubation of these cells suspended in nominally calcium-free medium with 0.1 μM thapsigargin resulted in a complete release of Ca2+ from intracellular calcium stores. When the medium was supplemented with 3 mM CaCl2 the cells maintained constantly elevated level of cytosolic Ca2+. However, thapsigargin applied at lower concentration produced only a partial depletion of the stores. For example, in the cells pretreated with 1 nM thapsigargin and suspended in calcium-free medium approximately 75% of the calcium content was released from the intracellular stores. The addition of 3 mM CaCl2 to such cell suspension led to a transient increase in cytosolic calcium concentration, followed by a return to a lower steady-state. This phenomenon, related to the refilling of the ER by Ca2+, allowed to estimate the half-time for the process of cell recovery after activation of store-operated calcium channels. By this approach we have found that carbonyl cyanide m-chlorophenylhydrazone, which has been documented to inhibit calcium entry into Jurkat cells, does not influence the stability of the intracellular signal involved in the activation of store-operated calcium channels.
EN
In the search for potential therapeutics, isoxazole derivatives are still objects of interest. Previously described immunoregulatory properties of 5-amino-3-methyl-4-isoxazolecarboxylic acid (AC) benzylamides prompted us to synthesize a new class of compounds of immunotropic activity. A series of new compounds containing the isoxazole moiety were synthesized using Passerini three-component reaction. The effects on phytohemagglutinin A (PHA)-induced proliferation of human peripheral blood mononuclear cells (PBMC), production of tumor necrosis factor alpha (TNF α) in human whole blood cultures stimulated with lipopolysaccharide (LPS) and two-way mixed lymphocyte reaction (MLR) of PBMC, were investigated. Also, the effect of 1-(cyclohexylcarbamoyl)cyclohexyl 5-amino-3-methylisoxazole-4-carboxylate (PUB1) on the expression of signaling molecules associated with cell apoptosis in Jurkat cells was also determined. The results showed that the compounds inhibited to various degree mitogen-induced PBMC proliferation in a dose-dependent manner and TNF α production at 10 μg/ml. PUB1 compound, selected on the basis of its strongest antiproliferative activity, was also shown to inhibit MLR. The molecular data suggest that immunosuppressive action of PUB1 depended on induction of Fas and elevation of caspase 8 expression. In summary, we revealed immunosuppressive properties of a new class of isoxazoles and established the mechanism of action of a representative PUB1 compound.
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2000
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vol. 47
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issue 3
591-599
EN
The participation of phospholipase A2 isoforms in capacitative store-operated Ca2+ influx into Jurkat leukemic T and MDCK cells was investigated. Preincubation of Jurkat cells with either bromophenacyl bromide (an inhibitor of secreted phospholipase A2, sPLA2) or Helss (an inhibitor of calcium independent phospholipase A2 - iPLA2) resulted in a significant inhibition of the calcium influx. The extent of this inhibition depended on the pH of the extracellular millieu; it increased with alkalisation. The rate of Ca2+ influx into MDCK cells was reduced by bromophenacyl bromide. Preincubation of these cells with Helss resulted in the stimulation of the influx. These observations suggest the participation of different PLA2 isoforms in the regulation of Ca2+ influx. They also show that the extent that PLA2 isoforms control the influx depends on the pH of the medium. Finally, these data indicate that various phospholipase A2 isoforms may play a role in the control of Ca2+ influx in different cell lines.
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