PAF-induced kinase activity of PKCα and inhibitory effect of Ro31-8220 and low Ca2+ in HEC-1B cell. (A) shows the effect of Ro 31-8220 on PAF mediated kinase activity in immunoprecipitates of PKCα. In some experiments, cells were pretreated for 30 min with 10 µM Ro31-8220 and challenged for 1hr with 1 nM or 10 nM PAF. Lysates of cells were immunoprecipitated with PKCα antisera and kinase reactions performed with histome H1 (H1) as decribed in the methods section. (B) shows the effect of removing Ca2+ from the medium on PAF stimulation of PKCα activity. Cells were incubated in Hank’s balanced salt solution (HBSS) with and without Ca2+ and challenged with 1 and 10 nM PAF. The kinase activity in PKCα immunoprecipitates is shown in the graph.