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 : ENVIRONMENTAL AND STRESS RESPONSES : MEMBARANES AND BIOENERGETICS

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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 in-creasing 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.
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