title: Cytosolic nucleotides block and regulate the Arabidopsis vacuolar anion channel AtALMT9.
abstract: The aluminum-activated malate transporters (ALMTs) form a membrane protein family exhibiting different physiological roles in plants, varying from conferring tolerance to environmental Al(3+) to the regulation of stomatal movement. The regulation of the anion channels of the ALMT family is largely unknown. Identifying intracellular modulators of the activity of anion channels is fundamental to understanding their physiological functions. In this study we investigated the role of cytosolic nucleotides in regulating the activity of the vacuolar anion channel AtALMT9. We found that cytosolic nucleotides modulate the transport activity of AtALMT9. This modulation was based on a direct block of the pore of the channel at negative membrane potentials (open channel block) by the nucleotide and not by a phosphorylation mechanism. The block by nucleotides of AtALMT9-mediated currents was voltage dependent. The blocking efficiency of intracellular nucleotides increased with the number of phosphate groups and ATP was the most effective cellular blocker. Interestingly, the ATP block induced a marked modification of the current-voltage characteristic of AtALMT9. In addition, increased concentrations of vacuolar anions were able to shift the ATP block threshold to a more negative membrane potential. The block of AtALMT9-mediated anion currents by ATP at negative membrane potentials acts as a gate of the channel and vacuolar anion tune this gating mechanism. Our results suggest that anion transport across the vacuolar membrane in plant cells is controlled by cytosolic nucleotides and the energetic status of the cell.
authors.affiliation: From the Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland and.
authors.forename: Jingbo
authors.initials: J
authors.lastname: Zhang
authors.affiliation: From the Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland and enrico.martinoia@botinst.uzh.ch.
authors.forename: Enrico
authors.initials: E
authors.lastname: Martinoia
authors.affiliation: From the Institute of Plant Biology, University of Zurich, CH-8008 Zurich, Switzerland and the Institut des Sciences du Végétal, CNRS, 91198 Gif-sur-Yvette, France alexis.de-angeli@isv.cnrs-gif.fr.
authors.forename: Alexis
authors.initials: A
authors.lastname: De Angeli
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism*; D000535:Aluminum / Q000737:chemistry / Q000378:metabolism*; D000838:Anions / Q000737:chemistry / Q000378:metabolism; D017360:Arabidopsis / Q000737:chemistry / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism*; D018118:Chloride Channels / Q000737:chemistry / Q000378:metabolism*; D003600:Cytosol / Q000737:chemistry / Q000378:metabolism; D017136:Ion Transport; D008564:Membrane Potentials; D014617:Vacuoles / Q000737:chemistry / Q000378:metabolism
chemical_list: C584418:ALMT9 protein, Arabidopsis; D000838:Anions; D029681:Arabidopsis Proteins; D018118:Chloride Channels; D000255:Adenosine Triphosphate; D000535:Aluminum
keywords: ATP; Chloride Channels; Chloride Transport; Electrophysiology; Intracellular; Malate; Membrane Biophysics; Membrane Transport; Open Channel Blocker