Mechanisms of Mg2+ inhibition of BzATP-dependent Ca2+ responses in THP-1 monocytes.
We have recently reported effects of Mg2+ to confer neuroprotection against toxicity of purinergic stimulated microglia and THP-1 monocytes. To examine mechanisms underlying neuroprotection, we have studied Mg2+ modulation of transient changes in intracellular Ca2+ ([Ca2+]i) in THP-1 cells induced by P2X7R agonist 2',3'-[benzoyl-4-benzoyl]-ATP (BzATP). Application of BzATP caused a rapid transient increase in [Ca2+]i followed by a prolonged component. The time course of the secondary slower phase was significantly reduced with Ca2+-free extracellular solution, with treatment of THP-1 cells by the P2X7R antagonist, oxATP or with exposure of cells to the store-operated channel (SOC) inhibitor, SKF96365. These results suggest that Ca2+ influx, mediated by both the P2X7R or by SOC, contribute to the slow component of [Ca2+]i. Treatment of THP-1 cells with 10 mMMg2+ was highly effective in reducing the time course of BzATP-induced Ca2+ decay; unlike the other modulatory protocols, Mg2+ markedly inhibited the amplitudes of slow and rapid components. In addition, acute application of Mg2+ during BzATP-induced responses elicited in the presence of either oxATP or SKF96365 to block respective P2X7R and SOC contributions, rapidly attenuated [Ca2+]i to baseline levels. Priming of cells with the inflammatory stimulus LPS/IFN-γ markedly enhanced the slower, but not rapid, phase of BzATP-induced [Ca2+]i with application of 10 mMMg2+ inhibiting both components of response. A model is proposed to account for BzATP stimulation of both ionotropic P2XR and metabotropic P2YR which provides a mechanistic basis for elevated Mg2+ anti-inflammatory and neuroprotective actions in inflamed brain.
Department of Anesthesiology, Pharmacology and Therapeutics, 2176 Health Sciences Mall, University of British Columbia, Vancouver, BC, Canada.
Nattinee
N
Jantaratnotai
Patrick L
PL
McGeer
James G
JG
McLarnon
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D045744:Cell Line, Tumor; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007371:Interferon-gamma / Q000276:immunology; D008070:Lipopolysaccharides / Q000276:immunology; D008274:Magnesium / Q000494:pharmacology*; D008954:Models, Biological; D009000:Monocytes / Q000276:immunology / Q000378:metabolism*; D058911:Purinergic P2X Receptor Agonists / Q000494:pharmacology; D058920:Purinergic P2X Receptor Antagonists / Q000494:pharmacology; D058486:Receptors, Purinergic P2X7 / Q000378:metabolism; D058470:Receptors, Purinergic P2Y / Q000378:metabolism
D007093:Imidazoles; D008070:Lipopolysaccharides; D058911:Purinergic P2X Receptor Agonists; D058920:Purinergic P2X Receptor Antagonists; D058486:Receptors, Purinergic P2X7; D058470:Receptors, Purinergic P2Y; C033901:3'-O-(4-benzoyl)benzoyladenosine 5'-triphosphate; C017199:2',3'-dialdehyde ATP; D007371:Interferon-gamma; D000255:Adenosine Triphosphate; D008274:Magnesium; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D002118:Calcium