Effects of three different Ca2+-ATPase inhibitors on Ca2+ response and leukotriene release in RBL-2H3 cells

The effects of three Ca2+-ATPase inhibitors, thapsigargin (TG), cyclopiazonic acid (CPA), and 2,5-di(tert-butyl)-1,4-hydroquinone (DTBHQ), on the Ca2+ response, degranulation, and leukotriene C-4 (LTC(4)) release in RBL-2H3 cells were investigated. All three compounds elevated the intracellular free Ca2+ concentration ([Ca2+](i)), and caused degranulation in the presence of 12-O-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C activator. The dose-dependency of each compound in the Ca2+ response was in good agreement with that in degranulation. TG and CPA also caused the release of LTC(4) in a dose-dependent manner, and this effect was unaffected by TPA or calphostin C, a selective PKC inhibitor. DTBHQ, however, did not induce LTC(4) release, and rather inhibited the antigen-induced release of LTC(4). These results suggest [1] that both degranulation and LTC(4) release caused by these compounds are dependent on their [Ca2+](i) increasing effect, [2] that degranulation and LTC(4) release are mediated via independent pathways following the Ca2+ response, and [3] that DTBHQ additionally prevents the synthesis of LTC(4) possibly by inhibition of 5-lipoxygenase.