The development of the
in vitro culturing technique of
Plasmodium falciparum by Trager and Jensen[
1] revolutionized the understanding of various aspects in the life cycle of this deadly parasite. The adoption of this technique in the research of malaria enabled the development of biochemical, physiological, immunological and genetic techniques[
2‐
5] which resulted in a more comprehensive understanding of the biology of the parasite. In spite of this advancement, falciparum malaria remains the most prevalent infectious disease resulting in a high level of morbidity and mortality[
6]. The major reasons for this state is the lack of an appropriate vaccine[
7,
8] and the evolving phenomenon of anti-malarial drug resistance[
9,
10]. The gaps which still exist in understanding the biology of the parasite contribute, although to a lesser extent, to this state. Since much of the studies on
P. falciparum are done on the intact infected red blood cell (RBC) unit, it is preferable to be able to localize unequivocally the activity within the infected unit. This paper describes an assay of that nature which localizes heavy metal resistance to the parasite itself. By comparing heavy metal resistant and sensitive
P. falciparum lines, it was previously shown[
11] that this property, which prevents the accumulation of the heavy metal, is probably determined by the parasite's
P. falciparum multidrug resistance 2 (
pfmdr2) gene. However, as the labelling technique used a radioactive heavy metal, it was not possible to assess the resistance/sensitivity state at the level of a single infected RBC whereas the technique described in this paper allows it. This was achieved by dual labelling with Fluo-3/AM which labels the heavy metal whose transport is studied and Hoechst which labels the parasite by binding to its DNA. Fluo-3/AM was scarcely used in the study of
P. falciparum and in those cases it served for determination of Ca
+2 metabolism[
12‐
15]. Hoechst and derivatives is used more commonly and in all cases for the visualization of the parasite e.g.[
16‐
20]. No dual labelling with these two dyes was reported hitherto in the literature.