Antiplasmodial effects of PBR ligands. (A) Cultures of the 3D7 strain synchronized at ring stage (in 96-well plates at 1.5% parasitemia and 2% hematocrit) were exposed to different concentrations of PBR ligands PK11195, Ro5-4864 and diazepam during 72 hours at 37°C. Their effects were compared with effects of antimalarial drug chloroquine (CQ) and anionic channels NPPB. Inhibition of parasite growth was evaluated by comparison of the total parasitemia to the negative control where cultures were treated with the solvent (DMSO) only. The lines connecting the experimental points were drawn according to nonlinear regression analysis of the experimental results converted into percent values. Each count was made in triplicate and each point on the curves corresponds to the mean (± SEM) of 3 separate experiments. (B,C,D) In sorbitol lysis experiments, culture suspensions were prepared as described in “Electrophysiology.” The effects of diazepam (B), PK11195 (C) and Ro5-4864 (D) added at t = 0 minutes of lysis experiments at concentrations below and above their IC₅₀s were tested by comparison to nontreated cells when haemolysis was at maximum at t = 60 minutes. Each count was made in triplicate and each point on the curves correspond to the mean (± SEM) of 3 separate experiments. Note that Ro5-4864 was not tested at 500 μM because of solubility limitation. (E-H) The whole-cell membrane conductance of infected RBCs was calculated by measurement of the amplitude of currents obtained by evoking a series of test potentials (VT) from −100 to +100 mV in 10 mV steps for 500 ms from a holding potential (VH) of 0 mV in the whole-cell configuration of the patch-clamp technique before and 15 minutes after addition of a ligand. The examples of panels E and F were obtained before and 15 minutes after addition of 100μM PK11195 to the bathing solution containing (in mmol/l) 115 NaCl, 5 KCl, 10 MgCl₂, 5 CaCl₂, 10 Hepes, 10 glucose, 1% human serum, pH 7.4. The pipette solution contained 155 NMDG-Cl, 1 MgCl2, 10 HEPES (pH 7.4). The calcium concentration was adjusted to pCa 3 in the bathing solution and to pCa 7 in the pipette solution. The impacts of the 3 different ligands were assessed by calculating the percentage reduction of inward conductance (G), (cord conductance between −100 mV and 0 mV) and outward conductance (H), (cord conductance between 0 mV and +100 mV). Bars are means ± SEM from 6 experiments.