Identification and Characterization of the Inward K^+ Channel in the Plasma Membrane of Brassica Pollen Protoplasts

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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 Ba^<2+> 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 Ca^<2+> concentrations from 10 nM to 30 μM or even 5 mM did not affect the inward K^+ currents. Decrease of external Ca^<2+> concentrations from 10 mM to 1 mM inhibited the inward K^+ currents by 25%, while the increase of external Ca^<2+> 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.
日本植物生理学会の論文