Skip to main content
NCBI home page
The EMBO Journal logoLink to The EMBO Journal
. 1997 May 15;16(10):2565–2575. doi: 10.1093/emboj/16.10.2565

New structure and function in plant K+ channels: KCO1, an outward rectifier with a steep Ca2+ dependency.

K Czempinski 1, S Zimmermann 1, T Ehrhardt 1, B Müller-Röber 1
PMCID: PMC1169868  PMID: 9184204

Abstract

Potassium (K+) channels mediating important physiological functions are characterized by a common pore-forming (P) domain. We report the cloning and functional analysis of the first higher plant outward rectifying K+ channel (KCO1) from Arabidopsis thaliana. KCO1 belongs to a new class of 'two-pore' K+ channels recently described in human and yeast. KCO1 has four putative transmembrane segments and tandem calcium-binding EF-hand motifs. Heterologous expression of KCO1 in baculovirus-infected insect (Spodoptera frugiperda) cells resulted in outwardly rectifying, K+-selective currents elicited by depolarizing voltage pulses in whole-cell measurements. Activation of KCO1 was strongly dependent on the presence of nanomolar concentrations of cytosolic free Ca2+ [Ca2+]cyt. No K+ currents were detected when [Ca2+]cyt was adjusted to <150 nM. However, KCO1 strongly activated at increasing [Ca2+]cyt, with a saturating activity observed at approximately 300 nM [Ca2+]cyt. KCO1 single channel analysis on excised membrane patches, resulting in a single channel conductance of 64 pS, confirmed outward rectification as well as Ca2+-dependent activation. These data suggest a direct link between calcium-mediated signaling processes and K+ ion transport in higher plants. The identification of KCO1 as the first plant K+ outward channel opens a new field of structure-function studies in plant ion channels.

Full Text

The Full Text of this article is available as a PDF (717.7 KB).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Anderson J. A., Huprikar S. S., Kochian L. V., Lucas W. J., Gaber R. F. Functional expression of a probable Arabidopsis thaliana potassium channel in Saccharomyces cerevisiae. Proc Natl Acad Sci U S A. 1992 May 1;89(9):3736–3740. doi: 10.1073/pnas.89.9.3736. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Atkinson N. S., Robertson G. A., Ganetzky B. A component of calcium-activated potassium channels encoded by the Drosophila slo locus. Science. 1991 Aug 2;253(5019):551–555. doi: 10.1126/science.1857984. [DOI] [PubMed] [Google Scholar]
  3. Barrett J. N., Magleby K. L., Pallotta B. S. Properties of single calcium-activated potassium channels in cultured rat muscle. J Physiol. 1982 Oct;331:211–230. doi: 10.1113/jphysiol.1982.sp014370. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Cao Y., Anderova M., Crawford N. M., Schroeder J. I. Expression of an outward-rectifying potassium channel from maize mRNA and complementary RNA in Xenopus oocytes. Plant Cell. 1992 Aug;4(8):961–969. doi: 10.1105/tpc.4.8.961. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Cao Y., Ward J. M., Kelly W. B., Ichida A. M., Gaber R. F., Anderson J. A., Uozumi N., Schroeder J. I., Crawford N. M. Multiple genes, tissue specificity, and expression-dependent modulationcontribute to the functional diversity of potassium channels in Arabidopsis thaliana. Plant Physiol. 1995 Nov;109(3):1093–1106. doi: 10.1104/pp.109.3.1093. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Chomczynski P., Sacchi N. Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction. Anal Biochem. 1987 Apr;162(1):156–159. doi: 10.1006/abio.1987.9999. [DOI] [PubMed] [Google Scholar]
  7. Devereux J., Haeberli P., Smithies O. A comprehensive set of sequence analysis programs for the VAX. Nucleic Acids Res. 1984 Jan 11;12(1 Pt 1):387–395. doi: 10.1093/nar/12.1part1.387. [DOI] [PMC free article] [PubMed] [Google Scholar]
  8. Fieuw S., Müller-Röber B., Gálvez S., Willmitzer L. Cloning and expression analysis of the cytosolic NADP(+)-dependent isocitrate dehydrogenase from potato. Implications for nitrogen metabolism. Plant Physiol. 1995 Mar;107(3):905–913. doi: 10.1104/pp.107.3.905. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Gilroy S., Fricker M. D., Read N. D., Trewavas A. J. Role of Calcium in Signal Transduction of Commelina Guard Cells. Plant Cell. 1991 Apr;3(4):333–344. doi: 10.1105/tpc.3.4.333. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Goldstein S. A., Price L. A., Rosenthal D. N., Pausch M. H. ORK1, a potassium-selective leak channel with two pore domains cloned from Drosophila melanogaster by expression in Saccharomyces cerevisiae. Proc Natl Acad Sci U S A. 1996 Nov 12;93(23):13256–13261. doi: 10.1073/pnas.93.23.13256. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Hamill O. P., Marty A., Neher E., Sakmann B., Sigworth F. J. Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patches. Pflugers Arch. 1981 Aug;391(2):85–100. doi: 10.1007/BF00656997. [DOI] [PubMed] [Google Scholar]
  12. Iijima T., Hagiwara S. Voltage-dependent K channels in protoplasts of trap-lobe cells of Dionaea muscipula. J Membr Biol. 1987;100(1):73–81. doi: 10.1007/BF02209142. [DOI] [PubMed] [Google Scholar]
  13. Irving H. R., Gehring C. A., Parish R. W. Changes in cytosolic pH and calcium of guard cells precede stomatal movements. Proc Natl Acad Sci U S A. 1992 Mar 1;89(5):1790–1794. doi: 10.1073/pnas.89.5.1790. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Ketchum K. A., Poole R. J. Cytosolic calcium regulates a potassium current in corn (Zea mays) protoplasts. J Membr Biol. 1991 Feb;119(3):277–288. doi: 10.1007/BF01868732. [DOI] [PubMed] [Google Scholar]
  15. Ketchum K. A., Slayman C. W. Isolation of an ion channel gene from Arabidopsis thaliana using the H5 signature sequence from voltage-dependent K+ channels. FEBS Lett. 1996 Jan 2;378(1):19–26. doi: 10.1016/0014-5793(95)01417-9. [DOI] [PubMed] [Google Scholar]
  16. Kyte J., Doolittle R. F. A simple method for displaying the hydropathic character of a protein. J Mol Biol. 1982 May 5;157(1):105–132. doi: 10.1016/0022-2836(82)90515-0. [DOI] [PubMed] [Google Scholar]
  17. Lesage F., Guillemare E., Fink M., Duprat F., Lazdunski M., Romey G., Barhanin J. A pH-sensitive yeast outward rectifier K+ channel with two pore domains and novel gating properties. J Biol Chem. 1996 Feb 23;271(8):4183–4187. doi: 10.1074/jbc.271.8.4183. [DOI] [PubMed] [Google Scholar]
  18. Lesage F., Guillemare E., Fink M., Duprat F., Lazdunski M., Romey G., Barhanin J. TWIK-1, a ubiquitous human weakly inward rectifying K+ channel with a novel structure. EMBO J. 1996 Mar 1;15(5):1004–1011. [PMC free article] [PubMed] [Google Scholar]
  19. McAinsh M. R., Brownlee C., Hetherington A. M. Visualizing Changes in Cytosolic-Free Ca2+ during the Response of Stomatal Guard Cells to Abscisic Acid. Plant Cell. 1992 Sep;4(9):1113–1122. doi: 10.1105/tpc.4.9.1113. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. McAinsh M. R., Webb AAR., Taylor J. E., Hetherington A. M. Stimulus-Induced Oscillations in Guard Cell Cytosolic Free Calcium. Plant Cell. 1995 Aug;7(8):1207–1219. doi: 10.1105/tpc.7.8.1207. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Moran N., Ehrenstein G., Iwasa K., Mischke C., Bare C., Satter R. L. Potassium Channels in Motor Cells of Samanea saman: A Patch-Clamp Study. Plant Physiol. 1988 Nov;88(3):643–648. doi: 10.1104/pp.88.3.643. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Müller-Röber B., Ellenberg J., Provart N., Willmitzer L., Busch H., Becker D., Dietrich P., Hoth S., Hedrich R. Cloning and electrophysiological analysis of KST1, an inward rectifying K+ channel expressed in potato guard cells. EMBO J. 1995 Jun 1;14(11):2409–2416. doi: 10.1002/j.1460-2075.1995.tb07238.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Neher E. Correction for liquid junction potentials in patch clamp experiments. Methods Enzymol. 1992;207:123–131. doi: 10.1016/0076-6879(92)07008-c. [DOI] [PubMed] [Google Scholar]
  24. Perney T. M., Kaczmarek L. K. The molecular biology of K+ channels. Curr Opin Cell Biol. 1991 Aug;3(4):663–670. doi: 10.1016/0955-0674(91)90039-2. [DOI] [PubMed] [Google Scholar]
  25. Salkoff L., Jegla T. Surfing the DNA databases for K+ channels nets yet more diversity. Neuron. 1995 Sep;15(3):489–492. doi: 10.1016/0896-6273(95)90137-x. [DOI] [PubMed] [Google Scholar]
  26. Schachtman D. P., Schroeder J. I., Lucas W. J., Anderson J. A., Gaber R. F. Expression of an inward-rectifying potassium channel by the Arabidopsis KAT1 cDNA. Science. 1992 Dec 4;258(5088):1654–1658. doi: 10.1126/science.8966547. [DOI] [PubMed] [Google Scholar]
  27. Schroeder J. I., Raschke K., Neher E. Voltage dependence of K channels in guard-cell protoplasts. Proc Natl Acad Sci U S A. 1987 Jun;84(12):4108–4112. doi: 10.1073/pnas.84.12.4108. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Schroeder J. I., Ward J. M., Gassmann W. Perspectives on the physiology and structure of inward-rectifying K+ channels in higher plants: biophysical implications for K+ uptake. Annu Rev Biophys Biomol Struct. 1994;23:441–471. doi: 10.1146/annurev.bb.23.060194.002301. [DOI] [PubMed] [Google Scholar]
  29. Sentenac H., Bonneaud N., Minet M., Lacroute F., Salmon J. M., Gaymard F., Grignon C. Cloning and expression in yeast of a plant potassium ion transport system. Science. 1992 May 1;256(5057):663–665. doi: 10.1126/science.1585180. [DOI] [PubMed] [Google Scholar]
  30. Spalding E. P., Cosgrove D. J. Large plasma-membrane depolarization precedes rapid blue-light-induced growth inhibition in cucumber. Planta. 1989;178:407–410. [PubMed] [Google Scholar]
  31. Stoeckel H., Takeda K. Calcium-sensitivity of the plasmalemmal delayed rectifier potassium current suggests that calcium influx in pulvinar protoplasts from Mimosa pudica L. can be revealed by hyperpolarization. J Membr Biol. 1995 Jul;146(2):201–209. doi: 10.1007/BF00238009. [DOI] [PubMed] [Google Scholar]
  32. Tufty R. M., Kretsinger R. H. Troponin and parvalbumin calcium binding regions predicted in myosin light chain and T4 lysozyme. Science. 1975 Jan 17;187(4172):167–169. doi: 10.1126/science.1111094. [DOI] [PubMed] [Google Scholar]
  33. Van Duijn B., Ypey D. L., Libbenga K. R. Whole-Cell K+ Currents across the Plasma Membrane of Tobacco Protoplasts from Cell-Suspension Cultures. Plant Physiol. 1993 Jan;101(1):81–88. doi: 10.1104/pp.101.1.81. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Wegner L. H., Raschke K. Ion Channels in the Xylem Parenchyma of Barley Roots (A Procedure to Isolate Protoplasts from This Tissue and a Patch-Clamp Exploration of Salt Passageways into Xylem Vessels. Plant Physiol. 1994 Jul;105(3):799–813. doi: 10.1104/pp.105.3.799. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from The EMBO Journal are provided here courtesy of Nature Publishing Group

RESOURCES