title: Characterization of the Ca2+-gated and voltage-dependent K+-channel Slo-1 of nematodes and its interaction with emodepside.
abstract: The cyclooctadepsipeptide emodepside and its parent compound PF1022A are broad-spectrum nematicidal drugs which are able to eliminate nematodes resistant to other anthelmintics. The mode of action of cyclooctadepsipeptides is only partially understood, but involves the latrophilin Lat-1 receptor and the voltage- and calcium-activated potassium channel Slo-1. Genetic evidence suggests that emodepside exerts its anthelmintic activity predominantly through Slo-1. Indeed, slo-1 deficient Caenorhabditis elegans strains are completely emodepside resistant. However, direct effects of emodepside on Slo-1 have not been reported and these channels have only been characterized for C. elegans and related Strongylida. Molecular and bioinformatic analyses identified full-length Slo-1 cDNAs of Ascaris suum, Parascaris equorum, Toxocara canis, Dirofilaria immitis, Brugia malayi, Onchocerca gutturosa and Strongyloides ratti. Two paralogs were identified in the trichocephalids Trichuris muris, Trichuris suis and Trichinella spiralis. Several splice variants encoding truncated channels were identified in Trichuris spp. Slo-1 channels of trichocephalids form a monophyletic group, showing that duplication occurred after the divergence of Enoplea and Chromadorea. To explore the function of a representative protein, C. elegans Slo-1a was expressed in Xenopus laevis oocytes and studied in electrophysiological (voltage-clamp) experiments. Incubation of oocytes with 1-10 µM emodepside caused significantly increased currents over a wide range of step potentials in the absence of experimentally increased intracellular Ca2+, suggesting that emodepside directly opens C. elegans Slo-1a. Emodepside wash-out did not reverse the effect and the Slo-1 inhibitor verruculogen was only effective when applied before, but not after, emodepside. The identification of several splice variants and paralogs in some parasitic nematodes suggests that there are substantial differences in channel properties among species. Most importantly, this study showed for the first time that emodepside directly opens a Slo-1 channel, significantly improving the understanding of the mode of action of this drug class.
authors.affiliation: Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany; Global Drug Discovery, Animal Health, Parasiticides, Bayer HealthCare, Leverkusen, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Kulke
authors.affiliation: Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany.
authors.forename: Georg
authors.initials: G
authors.lastname: von Samson-Himmelstjerna
authors.affiliation: Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany.
authors.forename: Sandra M
authors.initials: SM
authors.lastname: Miltsch
authors.affiliation: Department of Infectious Diseases, College of Veterinary Medicine, The University of Georgia, Athens, Georgia, United States of America.
authors.forename: Adrian J
authors.initials: AJ
authors.lastname: Wolstenholme
authors.affiliation: Faculty of Veterinary Science, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Aaron R
authors.initials: AR
authors.lastname: Jex
authors.affiliation: Faculty of Veterinary Science, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Robin B
authors.initials: RB
authors.lastname: Gasser
authors.affiliation: Institute of Parasitology, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada.
authors.forename: Cristina
authors.initials: C
authors.lastname: Ballesteros
authors.affiliation: Institute of Parasitology, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada.
authors.forename: Timothy G
authors.initials: TG
authors.lastname: Geary
authors.affiliation: Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Keiser
authors.affiliation: Tropical Parasitic Diseases Unit, Northwick Park Institute for Medical Research, Harrow, Middlesex, United Kingdom.
authors.forename: Simon
authors.initials: S
authors.lastname: Townson
authors.affiliation: WE Biology, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany.
authors.forename: Achim
authors.initials: A
authors.lastname: Harder
authors.affiliation: Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Krücken
mesh_terms: D000818:Animals; D000871:Anthelmintics / Q000494:pharmacology*; D017173:Caenorhabditis elegans / Q000187:drug effects / Q000235:genetics; D029742:Caenorhabditis elegans Proteins / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D047630:Depsipeptides / Q000494:pharmacology*; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D018408:Patch-Clamp Techniques; D010802:Phylogeny; D014982:Xenopus laevis
chemical_list: D000871:Anthelmintics; D029742:Caenorhabditis elegans Proteins; D047630:Depsipeptides; D051036:Large-Conductance Calcium-Activated Potassium Channels; C494845:slo-1 protein, C elegans; D002118:Calcium; C468987:emodepside