Effect of Y-24180 on Ca2+ movement and proliferation in renal tubular cells

In canine renal tubular cells, the effect of Y-24180, a presumed specific platelet activating factor (PAF) receptor antagonist, on intracellular Ca(2+) concentration (Ca(2+)](i)) was measured by using fura-2 as a Ca(2+)-sensitive fluorescent probe. Y-24180 (0.1-10 microM) caused a rapid and sustained Ca(2+)](i) rise in a concentration-dependent manner. The Ca(2+)](i) rise was prevented by 30% by removal of extracellular Ca(2+), but was not changed by dihydropyridines, verapamil and diltiazem. Y-24180-induced Ca(2+) influx was confirmed by Mn(2+)-influx induced quench of fura-2 fluorescence. In Ca(2+)-free medium, thapsigargin, an inhibitor of the endoplasmic reticulum Ca(2+)-ATPase, caused a monophasic Ca(2+)](i) rise, after which the increasing effect of 5 microM Y-24180 on Ca(2+)](i) was abolished; conversely, depletion of Ca(2+) stores with 5 microM Y-24180 abolished thapsigargin-induced Ca(2+)](i) rise. U73122, an inhibitor of phoispholipase C, inhibited ATP-, but not Y-24180-induced Ca(2+)](i) rise. Overnight treatment with Y-24180 did not alter cell proliferation rate. Collectively, these results suggest that Y-24180 acts as a potent, but not cytotoxic, Ca(2+) mobilizer in renal tubular cells, by stimulating both extracellular Ca(2+) influx and intracellular Ca(2+) release. Since alterations in Ca(2+) movement may interfere many cellular signaling processes unrelated to modulation of PAF receptors, caution must be applied in using this chemical as a selective PAF receptor antagonist.