Effects Of Mk-886, A Leukotriene Synthesis Inhibitor, On [Ca2+](I) And Apoptosis In Mg63 Human Osteosarcoma Cells

The effect of MK-886 (3-[1-(p-chlorobenzyl)-5-(isopropyl)-3-tert-butylthioindol-2-yl]-2, 2-dimethylpropanoic acid), a compound widely used to inhibit leukotriene synthesis, on cytosolic free Ca2+ concentrations ([Ca2+](i)) in osteosarcoma cells has not been explored. This study examined whether MK-886 altered [Ca2+](i) levels in suspended MG63 human osteosarcoma cells using fura-2. MK-886 at 0.1 mu M and above increased [Ca2+](i) in a concentration-dependent manner. The Ca2+ signal was reduced partly by removing extracellular Ca2+. MK-886 induced Mn2+ quenching of fura-2 fluorescence, implicating Ca2+ entry. MK-886-induced Ca2+ influx was inhibited by store-operated Ca2+ entry inhibitors, nifedipine, econazole, and SKF96365; and by the protein kinase C modulators, phorbol 12-myristate 13-acetate (PMA) and GF109203X. In Ca2+-free medium, after pretreatment with 5 mu M MK-886, 1 mu M thapsigargin (an encloplasmic reticulum Ca2+ pump inhibitor)-induced [Ca2+](i) rises were abolished; conversely, thapsigargin pretreatment nearly abolished MK-886-induced [Ca2+](i) rises. Inhibition of phospholipase C with U73122 did not change MK-886-induced [Ca2+](i) rises. Collectively, in MG63 osteosarcoma cells, MK-886 induced [Ca2+](i) rises by causing phospholipase C-independent Ca2+ release from the encloplasmic reticulum and Ca2+ influx via protein kinase C-regulated store-operated Ca2+ entry.