Figure 1.

FcεRI cross-linking activates both isoforms of PLCγ and PLCγ1 activation is selectively blocked by wortmannin. PLC activity was measured in anti-PLCγ immune complexes prepared from resting and antigen-stimulated RBL-2H3 cells from the hydrolysis of [³H]-PtdIns(4,5)P₂ in the Triton-based mixed micelle assay described in MATERIALS AND METHODS. Results show activation of PLCγ1(A) and PLCγ2 (B) at 2 and 10 min after addition of cross-linking reagent (1 μg/ml DNP-BSA) to control cells (open bars). PLCγ1 activation, but not that of PLCγ2, is inhibited in cells pretreated for 15 min with 10 nM wortmannin (hatched bars). Results are the average of duplicate samples in one of at least two similar experiments. Inset: The time course of antigen-induced Ins(1,4,5)IP₃ production in control cells, measured with the radioreceptor assay described in Deanin et al. (1991).