title: Nucleotides and Mg2+ ions differentially regulate K+ channels and non-selective cation channels present in cells forming the stomatal complex.
abstract: Voltage-dependent inward-rectifying (K(in)) and outward-rectifying (K(out)) K(+) channels are capable of mediating K(+) fluxes across the plasma membrane. Previous studies on guard cells or heterologously expressed K(+) channels provided evidence for the requirement of ATP to maintain K(+) channel activity. Here, the nucleotide and Mg(2+) dependencies of time-dependent K(in) and K(out) channels from maize subsidiary cells were examined, showing that MgATP as well as MgADP function as channel activators. In addition to K(out) channels, these studies revealed the presence of another outward-rectifying channel type (MgC) in the plasma membrane that however gates in a nucleotide-independent manner. MgC represents a new channel type distinguished from K(out) channels by fast activation kinetics, inhibition by elevated intracellular Mg(2+) concentration, permeability for K(+) as well as for Na(+) and insensitivity towards TEA(+). Similar observations made for guard cells from Zea mays and Vicia faba suggest a conserved regulation of channel-mediated K(+) and Na(+) transport in both cell types and species.
authors.affiliation: Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute for Bioscience, University of Wuerzburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Wolf
authors.forename: David Roger
authors.initials: DR
authors.lastname: Guinot
authors.forename: Rainer
authors.initials: R
authors.lastname: Hedrich
authors.forename: Petra
authors.initials: P
authors.lastname: Dietrich
authors.forename: Irene
authors.initials: I
authors.lastname: Marten
mesh_terms: D002413:Cations, Divalent; D007473:Ion Channels / Q000502:physiology*; D008274:Magnesium / Q000502:physiology*; D009711:Nucleotides / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000502:physiology*; D031307:Vicia faba / Q000502:physiology; D003313:Zea mays / Q000502:physiology
chemical_list: D002413:Cations, Divalent; D007473:Ion Channels; D009711:Nucleotides; D015221:Potassium Channels; D008274:Magnesium