title: The rice monovalent cation transporter OsHKT2;4: revisited ionic selectivity.
abstract: The family of plant membrane transporters named HKT (for high-affinity K(+) transporters) can be subdivided into subfamilies 1 and 2, which, respectively, comprise Na(+)-selective transporters and transporters able to function as Na(+)-K(+) symporters, at least when expressed in yeast (Saccharomyces cerevisiae) or Xenopus oocytes. Surprisingly, a subfamily 2 member from rice (Oryza sativa), OsHKT2;4, has been proposed to form cation/K(+) channels or transporters permeable to Ca(2+) when expressed in Xenopus oocytes. Here, OsHKT2;4 functional properties were reassessed in Xenopus oocytes. A Ca(2+) permeability through OsHKT2;4 was not detected, even at very low external K(+) concentration, as shown by highly negative OsHKT2;4 zero-current potential in high Ca(2+) conditions and lack of sensitivity of OsHKT2;4 zero-current potential and conductance to external Ca(2+). The Ca(2+) permeability previously attributed to OsHKT2;4 probably resulted from activation of an endogenous oocyte conductance. OsHKT2;4 displayed a high permeability to K(+) compared with that to Na(+) (permeability sequence: K(+) > Rb(+) ≈ Cs(+) > Na(+) ≈ Li(+) ≈ NH(4)(+)). Examination of OsHKT2;4 current sensitivity to external pH suggested that H(+) is not significantly permeant through OsHKT2;4 in most physiological ionic conditions. Further analyses in media containing both Na(+) and K(+) indicated that OsHKT2;4 functions as K(+)-selective transporter at low external Na(+), but transports also Na(+) at high (>10 mm) Na(+) concentrations. These data identify OsHKT2;4 as a new functional type in the K(+) and Na(+)-permeable HKT transporter subfamily. Furthermore, the high permeability to K(+) in OsHKT2;4 supports the hypothesis that this system is dedicated to K(+) transport in the plant.
authors: Biochimie et Physiologie Moléculaire des Plantes, Unité Mixte de Recherche, 5004 Centre National de la Recherche Scientifique/386 Institut National de la Recherche Agronomique/SupAgro-M/Université Montpellier 2, Campus SupAgro-M, Montpellier cedex 2, France.
authors: Ali
authors: A
authors: Sassi
authors: Delphine
authors: D
authors: Mieulet
authors: Imran
authors: I
authors: Khan
authors: Bertrand
authors: B
authors: Moreau
authors: Isabelle
authors: I
authors: Gaillard
authors: Hervé
authors: H
authors: Sentenac
authors: Anne-Aliénor
authors: AA
authors: Véry
mesh_terms: D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000378:metabolism; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D002463:Cell Membrane Permeability; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000378:metabolism; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D012275:Oryza / Q000378:metabolism*; D018408:Patch-Clamp Techniques / Q000379:methods; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism; D013045:Species Specificity; D014981:Xenopus / Q000235:genetics / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D027682:Cation Transport Proteins; D018076:DNA, Complementary; C434985:HKT2 protein, Oryza sativa; D010940:Plant Proteins; D015221:Potassium Channels; D015222:Sodium Channels; D008274:Magnesium; D011188:Potassium; D002118:Calcium