Investigating the Osmotic Component in Mechanisms of Malaria Parasite Plasmodium Falciparum Egress and Invasion of Human Red Blood Cells

Abstract

Human red blood cells (RBC) experience a transient echinocytic shape change immediately after parasite invasion and another within the last minutes before parasite egress when infected RBC seems to round up. The rapidity of shape changes in both events makes an osmotic mechanism a likely candidate. Indeed, it was shown that the rate of parasite egress is influenced by the osmolarity of the culture medium, suggesting the involvement of ion channels in the egress program and Aquaporin 1, a RBC water channel, was implicated in the initiation of the intraerythrocytic development of Plasmodium falciparum. Currently available methods are able to resolve infected red blood cell volume at the various stages of the 48h plasmodium developmental cycle, yet lack time resolution to capture fast-progressing events such as parasite egress and invasion of RBC. To gain insight into the putative osmotic component of these processes, we tested the suitability of a recently developed method for volume measurements of live cells, based on fluorescence exclusion, for volume evaluation in RBC during fast egress-invasion events in vitro. We show that volumes can be captured with video rate speed, high throughput, and sensitivity to relative changes of 0.3 µm3. We conclude that the fluorescence exclusion method is well suited for testing parasite egress-invasion events in real time and studying multiple individual events in the same cell suspension. Preliminary volume measurements of infected erythrocytes approaching parasite egress will be presented.