PKC activity in uninfected and P falciparum–infected erythrocytes. (A) PKC activity determined in cytosol and membrane fractions from uninfected erythrocytes (RBC) and enriched infected erythrocytes (IRBC) (60% parasitemia) incubated with DMSO (□) or 500 nmol/L PMA (▨) for 15 minutes. PKC activity given is the total kinase activity minus activity measured in the absence of lipid activators (PMA/Phosphatidyl-serine/Triton-X–100 mixed micelles) and the presence of 20 μmol/L PKC.19-36 Activities represent the mean of duplicate assays + range. This result is representative of six separate experiments. (B) Kinase activity in isolated parasites. IRBC (2.5 × 10⁷) were incubated with DMSO (□) or 500 nmol/L PMA (▨) for 15 minutes at 37°C. Parasites were prepared by saponin lysis, then fractionated as described.28 PKC activity was determined as described above. Values represent the mean of duplicate assays + range. This result is representative of three separate experiments. (C) Membrane PKC activity in RBC and IRBC (60% parasitemia) incubated with DMSO (□) or 500 nmol/L PMA (▨) for 15 minutes. PKC activity was determined as described above. Values represent the mean of triplicate assays + standard error of mean (SEM). This result is representative of six separate experiments.