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

Plasmodium falciparum is the causative agent of the deadliest human malaria. New molecules are needed that can specifically bind to erythrocytes that are infected with P. falciparum for diagnostic purposes, to disrupt host-parasite interactions, or to deliver chemotherapeutics. Aptamer technology has the potential to revolutionize biological diagnostics and therapeutics; however, broad adoption is hindered by the high failure rate of the systematic evolution of ligands by exponential enrichment (SELEX). Here we performed parallel SELEX experiments to compare the impact of two different methods for single-strand recovery on the efficiency of aptamer enrichment. Our experimental results and analysis of SELEX publications spanning 13 years implicate the alkaline denaturation step as a significant cause for inefficient aptamer selection. Thus, we applied an exonuclease single-strand recovery step in our SELEX to direct aptamers to the surface of erythrocytes infected with P. falciparum. The selected aptamers bind with high affinity (low nanomolar K d values) and selectivity to exposed surface proteins of both laboratory parasite strains as well isolates from patients in Asia and Africa with clinical malaria. The results obtained in this study potentially open new approaches to malaria diagnosis and surveillance. Malaria is a global health problem, with 228 million clinical episodes and an estimated 405,000 deaths each year 1. Plasmodium falciparum is the causative agent of the deadliest human malaria. A constellation of parasite-encoded proteins is displayed on the surface of infected erythrocytes (IEs) that are important in the life cycle of the parasite and mediate critical host-parasite interactions. One important host-parasite interaction is IE sequestration in the microvasculature which is thought to lead to the most severe manifestations of the disease. Therefore, ligand-binding molecules that can specifically identify and bind to IEs may disrupt important host-parasite interactions, deliver chemotherapeutics to parasitized cells, and have potential to further our understanding of the diversity of proteins expressed on the IE surface 2-5. Indeed, antibodies targeting IEs disrupt pathogenesis and contribute to naturally-acquired immunity to malaria 6-9. Aptamers are an alternative to antibodies that may sufficiently serve as molecular recognition agents of IEs. Several aptamers have been selected that bind to targets and biomarkers of malaria infection (see review 10 for examples). Aptamers are single-stranded nucleic acids that bind target molecules with antibody-like affinity and specificity through shape complementarity 11,12. However, the nucleic acid composition of aptamers presents several advantages over antibodies including increased stability, cell-free synthesis (either by PCR or chemical synthesis), and simple modification for detection and immobilization. Aptamers have been developed against small molecules, peptides, proteins, and whole cells including bacteria and parasites 3,13-16. As such, aptame...