title: Ca(2+)-permeable, outwardly-rectifying K+ channels in mesophyll cells of Arabidopsis thaliana.
abstract: Arabidopsis thaliana has become a powerful tool in genetics and molecular biology. In order to use Arabidopsis as a model system for electrophysiological studies on plant cells, a detailed characterization of the transporters present in the plasma and vacuolar membranes of this species is required. We used the patch-clamp technique to study ion channels in the plasma membrane of Arabidopsis mesophyll cells. The most prominent conductance in these cells was a K(+)-selective, voltage-dependent, outwardly-rectifying channel (IK,out). In the whole-cell configuration, IK,out was observed in 100% of the cells assayed. In contrast, inward current was observed in less than 50% of the cells which were bathed in 100 mM K+, and was totally absent from cells bathed in 10 mM K+. The activation kinetics of IK,out were modulated by the external K+ concentration with a faster activation at low external K+. Tail-current analysis revealed that in addition to K+, IK,out is also permeable to Ca2+ and Ba2+. Externally applied Ba2+ also caused a voltage-dependent decrease in current magnitude, indicating that IK,out is also partially blocked by this classic K+ channel blocker. Single channels studied in outside-out patches showed Ca2+ and Ba2+ sensitivity, voltage dependence and time activation similar to that of IK,out in the whole-cell configuration. Given their permeability to Ca2+, these channels may function as an avenue for Ca2+ influx as well as K+ efflux, both of which may affect photosynthesis.
authors.affiliation: Dept. of Biology, Pennsylvania State University, University Park 16802, USA.
authors.forename: L A
authors.initials: LA
authors.lastname: Romano
authors.forename: H
authors.initials: H
authors.lastname: Miedema
authors.forename: S M
authors.initials: SM
authors.lastname: Assmann
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000502:physiology*; D001464:Barium / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002463:Cell Membrane Permeability; D008564:Membrane Potentials / Q000187:drug effects; D015221:Potassium Channels / Q000502:physiology*
chemical_list: D015221:Potassium Channels; D001464:Barium; D002118:Calcium