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Identification and characterization of the inward K+ channel in the plasma membrane of Brassica pollen protoplasts

Fan, L.M., Wu, W.H., Yang, H.Y.
Plant & cell physiology 1999 v.40 no.8 pp. 859-865
Brassica rapa subsp. chinensis, potassium, ion transport, protoplasts, pollen, electric current, cesium, sodium, barium, culture media, cytoplasm, cations, plasma membrane, application rate, inorganic ions, calcium
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 micromolar 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.