Electrophysiological Characterization And Regulation Of Inward K～+ Channel In The Plasmamembrane Of Tobacco Root Cortex Cells

1. In an attempt to understand the mechanism of K⁺ uptake and the regulated factors, patch clamp whole-cell recording techniques were applied to protoplasts isolated from tobacco root cortex. The results showed activation of a large inward current by K⁺ ions into root cortex at membrane potentials more negative than -100 mV as the bath solution contained 100 mmol/L K⁺ and the pipette solution contained 10 mmol/L K⁺. The inward currents became larger with the membrane became more negative. The inward currents were strongly inhibited by the K⁺-channel blocker TEA⁺; The K⁺ current density depended on the extracellular K⁺ concentrations and the activation potential of inward currents shifted to more negative values with decreasing K⁺ concentrations; The inward K⁺-channel were sensitive to NH₄⁺ ions. The inward currents became smaller with the extracellular NH₄⁺ concentration increased; The inward currents were inhibited differently by Ca²⁺ or Mg²⁺. When the medium contained high concentrations of Ca²⁺ or Mg²⁺, the inward currents showed larger by high membrane potentials or showed smaller by lower membrane potentials with increasing the concentrations of K⁺; The K⁺-channel were highly selective for K⁺ over Na⁺ or Li⁺. The inward currents were strongly inhibited by Na⁺ or Li⁺ ions.2. The low-affinity transporter contributed significantly to K⁺ uptake when K⁺ concentration was 10 mmol/L in the solution culture experiments. â‘ The variation of...