title: Identification and characterization of the inward K+ channel in the plasma membrane of Brassica pollen protoplasts.
abstract: Patch clamp techniques have been used to identify and characterize the whole-cell currents carried by inward K+ channels in isolated matured pollen protoplasts of Brassica chinensis var. chinensis. The whole-cell inward currents in the isolated pollen protoplasts were activated at hyperpolarized membrane potentials more negative than -100 mV. The magnitudes of the whole-cell inward currents were strongly dependent on the external K+ concentration, and were highly selective for K+ over other monovalent cations. The inward currents were not observed when external K+ was replaced with the same concentration of Cs+ or Na+. The addition of 1 mM or 10 mM Ba2+ in external solutions resulted in 30% or 80% inhibition of the inward currents at -180 mV, respectively. These results demonstrated that the inward K+ currents mainly account for the recorded whole-cell inward currents in Brassica pollen protoplasts. Increase of cytoplasmic Ca2+ concentrations from 10 nM to 30 microM or even 5 mM did not affect the inward K+ currents. Decrease of external Ca2+ concentrations from 10 mM to 1 mM inhibited the inward K+ currents by 25%, while the increase of external Ca2+ from 10 mM to 50 mM almost completely blocked the inward K+ currents. Physiological importance of K+ transport into pollen and its possible regulatory mechanisms are also discussed.
authors.affiliation: Department of Plant Sciences, College of Biological Sciences, China Agricultural University, Beijing, China.
authors.forename: L M
authors.initials: LM
authors.lastname: Fan
authors.forename: W H
authors.initials: WH
authors.lastname: Wu
authors.forename: H Y
authors.initials: HY
authors.lastname: Yang
mesh_terms: D001937:Brassica / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D011058:Pollen / Q000378:metabolism*; D015221:Potassium Channels / Q000378:metabolism / Q000502:physiology*; D024661:Potassium Channels, Inwardly Rectifying; D011523:Protoplasts / Q000378:metabolism*
chemical_list: D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying