title: High guanidinium permeability reveals dehydration-dependent ion selectivity in the plasmodial surface anion channel.
abstract: Malaria parasites grow within vertebrate erythrocytes and increase host cell permeability to access nutrients from plasma. This increase is mediated by the plasmodial surface anion channel (PSAC), an unusual ion channel linked to the conserved clag gene family. Although PSAC recognizes and transports a broad range of uncharged and charged solutes, it must efficiently exclude the small Na(+) ion to maintain infected cell osmotic stability. Here, we examine possible mechanisms for this remarkable solute selectivity. We identify guanidinium as an organic cation with high permeability into human erythrocytes infected with Plasmodium falciparum, but negligible uptake by uninfected cells. Transport characteristics and pharmacology indicate that this uptake is specifically mediated by PSAC. The rank order of organic and inorganic cation permeabilities suggests cation dehydration as the rate-limiting step in transport through the channel. The high guanidinium permeability of infected cells also allows rapid and stringent synchronization of parasite cultures, as required for molecular and cellular studies of this pathogen. These studies provide important insights into how nutrients and ions are transported via PSAC, an established target for antimalarial drug development.
authors.affiliation: The Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
authors.forename: Abdullah A B
authors.initials: AA
authors.lastname: Bokhari
authors.affiliation: The Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
authors.forename: Neida K
authors.initials: NK
authors.lastname: Mita-Mendoza
authors.affiliation: The Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Fuller
authors.affiliation: The Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
authors.forename: Ajay D
authors.initials: AD
authors.lastname: Pillai
authors.affiliation: The Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852, USA.
authors.forename: Sanjay A
authors.initials: SA
authors.lastname: Desai
mesh_terms: D002463:Cell Membrane Permeability / Q000502:physiology*; D003681:Dehydration; D004910:Erythrocyte Membrane / Q000378:metabolism*; D004912:Erythrocytes / Q000378:metabolism / Q000469:parasitology; D019791:Guanidine / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007473:Ion Channels / Q000737:chemistry / Q000378:metabolism*; D016778:Malaria, Falciparum / Q000378:metabolism / Q000469:parasitology; D010963:Plasmodium falciparum
chemical_list: D007473:Ion Channels; C505335:surface anion channel protein, Plasmodium falciparum; D019791:Guanidine