In situ PKC activity in uninfected and infected erythrocytes. (A) Dose-dependent PKC activation by PMA. PKC activity in uninfected erythrocytes (▪) and 65% infected erythrocytes (▴) prepared as described in Materials and Methods section and incubated for 15 minutes at 37°C with various concentrations of PMA. Results represent the mean of triplicate values ± SEM. Non-PKC activity in uninfected (□) and infected (▵) cells, as measured in the absence of Ca²⁺ and the presence of 50 μmol/L PKC,19-31 represents the mean of duplicate values. These results are representative of three separate experiments. (B) Time course of PKC activation by PMA. PKC activity in uninfected erythrocytes (▪) and 55% infected erythrocytes (▴) prepared as described in Materials and Methods and incubated with 500 nmol/L PMA at 37°C for various times. Results represent the mean of triplicate values ± SEM. Non-PKC activity in uninfected (□) and infected (▵) cells, as measured in the absence of Ca²⁺ and the presence of 50 μmol/L PKC,19-31 represents the mean of duplicate values. These results are representative of three separate experiments. (C) Effect of parasitemia on PKC activity. Plasmagel-enriched parasites were diluted to various parasitemias with cells from the same culture before enrichment and incubated for 15 minutes with 500 nmol/L PMA. Results given represent the mean of triplicate assays ± SEM.