Novel effect of Y-24180, a presumed specific platelet-activating factor receptor antagonist, on Ca2+ levels and growth of human osteosarcoma cells

In human osteosarcoma MG63 cells, the effect of Y-24180, a presumed specific platelet-activating factor (PAF) receptor antagonist, on intracellular Ca2+ concentration ([Ca2+]i) and proliferation was measured by using fura-2 and tetrazolium as fluorescent dyes, respectively. Y-24180 (1-5 μM) caused a rapid and sustained [Ca2+]i rise in a concentration-dependent manner. The [Ca2+]i rise was inhibited by 35% by dihydropyridines or removal of extracellular Ca2+, but was not altered by verapamil and diltiazem. In Ca2+-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+-ATPase, caused a monophasic [Ca2+]i rise, after which 5 μM Y-24180 failed to increase [Ca2+]i; conversely, depletion of Ca2+ stores with 5 μM Y-24180 abolished thapsigargin-induced [Ca2+]i rise. U73122, an inhibitor of phoispholipase C, inhibited histamine-induced, but not 5 μM Y-24180-induced [Ca2+]i rise. Overnight treatment with 0.1-5 μM Y-24180 inhibited cell proliferation in a concentration-dependent manner. Together, these findings suggest that Y-24180 acts as a potent and cytotoxic Ca2+ mobilizer in human osteosarcoma cells, by inducing both extracellular Ca2+ influx and intracellular Ca2+ release. Alterations in cytosolic Ca2+ regulation may lead to interferences of various cellular functions; thus, attention should be exercised in using Y-24180 as a selective PAF receptor antagonist.