Role of phosphatidylinositol 3-kinase in degranulation induced by IgE-dependent and -independent mechanisms in rat basophilic RBL-2H3 (ml) cells

We have examined the role of phosphatidylinositol 3-kinase (PI3-kinase) in the degranulation induced by the antigen, an IgE-dependent stimulant, and by carbachol and thapsigargin, IgE-independent stimulants, in the muscarine ml receptor-transfected mast cell line RBL-2H3 (ml) cells. These stimulants commonly increased PI3-kinase activity in the anti-phosphotyrosine immunoprecipitate. The PI3-kinase inhibitors wortmannin and LY294002 inhibited the degranulation induced by these stimulants. The membrane ruffling induced by the antigen or carbachol was also inhibited by wortmannin. In contrast, thapsigargin induced by membrane ruffling but induced microspikes, which was not affected by wortmannin. In the permeabilized RBL-2H3 (ml) cells, wortmannin inhibited the GTPγS-induced membrane ruffling without inhibiting the GTPγS-induced degranulation. These findings suggest that PI3-kinase is involved not only in IgE-dependent degranulation but also in IgE-independent degranulation, and that the GTPγS sensitive protein at the downstream of PI3-kinase is responsible for the degranulation but not for the membrane ruffling.