Reduced permeability to K⁺ and Na⁺ ions of K⁺ channels in the plasma membrane of tobacco cells in suspension after adaptation to 50 mM NaCl

The whole-cell patch-clamp technique was used to study and compare the characteristics of K⁺-and Na⁺-transport processes across the plasma membrane in two types of protoplast isolated from NaCl-adapted and -unadapted cells of tobacco (Nicotiana tabacum L. cv. Bright Yellow-2) in suspension culture. In both types of protoplast, with 100 mM KCl in the bathing solution and in the pipette solution, depolarization of the plasma membrane from the holding potential of 0 mV to a positive potential resulted in a relatively large outward current which increased with increasing positive potential, whereas hyperpolarization to negative potentials up to -100 mV resulted in only a small inward current. The outward current activated by depolarization was predominantly carried by K⁺ ions through K⁺ channels. Na⁺ ions also had a finite ability to pass through these K⁺ channels. The outward K⁺ and Na⁺ currents of the NaCl-adapted cells were considerably smaller than those of the NaCl-unadapted cells. These results suggest that adaptation to salinity results in reduced permeability of the plasma membrane to both K⁺ and Na⁺ ions.