The Character of Inward K⁺-channels in the Plasma Membrane from Tobacco Root Cortex Protoplasts

To understand the mechanism of K⁺ uptake and the regulated factors,patch clamp whole-cell recording techniques were applied to isolated tobacco root cortex protoplasts.The results showed that the inward current were activated by K⁺ into root cortex at membrane potentials more negative than-40 mV.The inward currents were strongly inhibited by the K⁺-channel blocker TEA⁺ kinetic analysis of the inward currents yielded an apparent K⁺ equilibrium dissociation constant(K_m) of≈15.2 mmol/L,which closely correlated to the major component of low-affinity K⁺ uptake.The inward K⁺-channels were sensitive to NH₄⁺ and NH₄⁺ was acted on a bin-(ding) site external to the channel pore.The inward currents were inhibited differently by Ca²⁺ and Mg²⁺.It is suggested that the inward K⁺ channels in root cortex may function as both a physiologically important mechanism for low-affinity K⁺ uptake and regulators of membrane potentials.