Figure 4. Correlation between invasion and Ca²⁺ signal.

(a) T994 merozoites isolated from each Ca²⁺ measurement experiment (Fig. 3b) were also used in parallel to test invasion (Supplementary Table S3). The percentage of invasion (Parasitemia (%), horizontal axis) is plotted against the Ca²⁺ signals at t=600 s (≤ΔF (t=600 s), vertical axis) (Fig. 3b). Blue diamonds represent merozoites incubated with erythrocytes in the absence of mAbs (RBC). Green triangles represent merozoites incubated with erythrocytes in the presence of inhibitory mAb C41 (RBC+C41 (0.2 mg ml⁻¹)). Purple circles represent merozoites incubated with erythrocytes in the presence of non-inhibitory mAb C2 (RBC+C2 (0.2 mg ml⁻¹)). The R-square (R²) with value of 0.836 indicates strong correlation between invasion and Ca²⁺ signalling. (b) Merozoite invasion kinetics assay under heparin treatment. Freshly isolated T994 merozoites were allowed to invade erythrocytes followed by treatment with heparin (200 μg ml⁻¹) at different time points (2–10 min with 2 min interval) to inhibit invasion. After the final time point, cultures were incubated for 40 h, and resulting parasitemias were analysed by flow cytometry. The proportion of merozoites that have invaded with increasing time is shown as % of maximum invasion obtained in uninhibited culture. The rate of merozoite invasion over time is linear (R²=0.991). Experimental data are presented as the mean±s.e.m.; n=3.