title: Outward K+ channels in Brassica chinensis pollen protoplasts are regulated by external and internal pH.
abstract: Patch-clamp whole-cell and single-channel recording techniques were used to investigate the regulation of outward K(+) channels by external and internal protons in Brassica chinensispollen protoplasts. Outward K(+) currents and conductance were insensitive to external pH (pH(o)) except at pH 4.5. Maximal conductance (G(max)) for the outward K(+) currents was inhibited at acidic external pH. Half-activation voltage ( E(1/2)) for the outward K(+) currents shifted to more positive voltages along with the decrease in pH(o). E(1/2) can be described by a modified Henderson-Hasselbalch equation expected from a single titratable binding site. The activation kinetics of the outward K(+) channels was largely insensitive to pH(o). An internal pH (pH(i)) of 4.5 significantly increased outward K(+) currents and conductance. G(max) for the outward K(+) currents decreased with elevations in pH(i). In contrast to the effect of pH(o), E(1/2) was shifted to more positive voltages with elevations in pH(i). The outward K(+) currents, G(max) and E(1/2) can be described by the modified Henderson-Hasselbalch equation. Furthermore, acidifying pH(i) accelerated the activation of the outward K(+) currents significantly. The differences in electro-physiological properties among previously reported and currently described plant outward K(+) channels may reflect differences in the structure of these channels.
authors.affiliation: Department of Plant Sciences, State Key Laboratory in Plant Physiology, China Agricultural University, Beijing.
authors.forename: L-M
authors.initials: LM
authors.lastname: Fan
authors.forename: Y-F
authors.initials: YF
authors.lastname: Wang
authors.forename: W-H
authors.initials: WH
authors.lastname: Wu
mesh_terms: D001937:Brassica / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000502:physiology; D018408:Patch-Clamp Techniques; D010940:Plant Proteins / Q000502:physiology*; D011058:Pollen / Q000166:cytology / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology*; D011522:Protons; D011523:Protoplasts / Q000502:physiology*
chemical_list: D010940:Plant Proteins; D015221:Potassium Channels; D011522:Protons