Malaria symptoms occur during Plasmodium falciparum development into red blood cells. During this process, the parasites make substantial modifications to the host cell in order to facilitate nutrient uptake and aid in parasite metabolism. One significant alteration that is required for parasite development is the establishment of an anion channel, as part of the establishment of New Permeation Pathways (NPPs) in the red blood cell plasma membrane, and we have shown previously that one channel can be activated in uninfected cells by exogenous protein kinase A. Here, we present evidence that in P. falciparum-infected red blood cells, a cAMP pathway modulates anion conductance of the erythrocyte membrane. In patch-clamp experiments on infected erythrocytes, addition of recombinant PfPKA-R to the pipette in vitro, or overexpression of PfPKA-R in transgenic parasites lead to down-regulation of anion conductance. Moreover, this overexpressing PfPKA-R strain has a growth defect that can be restored by increasing the levels of intracellular cAMP. Our data demonstrate that the anion channel is indeed regulated by a cAMP-dependent pathway in P. falciparum-infected red blood cells. The discovery of a parasite regulatory pathway responsible for modulating anion channel activity in the membranes of P. falciparum-infected red blood cells represents an important insight into how parasites modify host cell permeation pathways. These findings may also provide an avenue for the development of new intervention strategies targeting this important anion channel and its regulation.

A recent study on malaria‐infected human red blood cells (RBCs) has shown induced ion channel activity in the host cell membrane, but the questions of whether they are host‐ or parasite‐derived and their molecular nature have not been resolved. Here we report a comparison of a malaria‐induced anion channel with an endogenous anion channel in Plasmodium falciparum‐infected human RBCs. Ion channel activity was measured using the whole‐cell, cell‐attached and excised inside‐out configurations of the patch‐clamp method. Parasitised RBCs were cultured in vitro, using co‐cultured uninfected RBCs as controls. Unstimulated uninfected RBCs possessed negligible numbers of active anion channels. However, anion channels could be activated in the presence of protein kinase A (PKA) and ATP in the pipette solution or by membrane deformation. These channels displayed linear conductance (∼15 pS), were blocked by known anion channel inhibitors and showed the permeability sequence I− > Br− > Cl−. In addition, in less than 5 % of excised patches, an outwardly rectifying anion channel (∼80 pS, outward conductance) was spontaneously active. The host membrane of malaria‐infected RBCs possessed spontaneously active anion channel activity, with identical conductances, pharmacology and selectivity to the linear conductance channel measured in stimulated uninfected RBCs. Furthermore, the channels measured in malaria‐infected RBCs were shown to have a low open‐state probability (Po) at positive potentials, which explains the inward rectification of membrane conductance observed when using the whole‐cell configuration. The data are consistent with the presence of two endogenous anion channels in human RBCs, of which one (the linear conductance channel) is up‐regulated by the malaria parasite P. falciparum.

The altered permeability characteristics of erythrocytes infected with malaria parasites have been a source of interest for over 30 years. Recent electrophysiological studies have provided strong evidence that these changes reflect transmembrane transport through ion channels in the host erythrocyte plasma membrane. However, conflicting results and differing interpretations of the data have led to confusion in this field. In an effort to unravel these issues, the groups involved recently came together for a week of discussion and experimentation. In this article, the various models for altered transport are reviewed, together with the areas of consensus in the field and those that require a better understanding. KeywordsPatch-clamp; Ion channels; New permeability pathways; PSAC; Plasmodium; Oxidation It has been known for several decades that Plasmodium falciparum-infected erythrocytes exhibit increased permeability to a wide range of structurally unrelated solutes as the internal parasite matures. These changes are thought to be important for the survival of the parasite. They may be involved in nutrient uptake, metabolite removal, volume regulation and/or