SALT ADAPTATION OF K+ CHANNELS IN THE PLASMA-MEMBRANE OF TOBACCO CELLS IN SUSPENSION-CULTURE

The patch-clamp technique was used to study and compare the characteristics of cation channels in the plasma membrane of cultured lines of tobacco (Nicotiana tabacum L. cv. Bright Yellow-2) cells that were unadapted (NaCl-unadapted cells) and adapted to 50 and 100 mM NaCl (NaSO-adapted and Na100-adapted cells). In these three types of tobacco cell, the outward whole-cell current activated by depolarization was dominated mainly by the activity of the outward rectifying K+ channels with a single-channel conductance of 20 pS. The steady-state amplitude of the outward whole-cell currents at all the positive potentials examined decreased in the following order: NaCl-unadapted cells >Na50-adapted cells >Na100-adapted cells. There were no significant differences between the NaCl-unadapted and the NaSO-adapted cells in terms of the ratio of permeabilities of these channels to K+ and Na+ ions. Furthermore, no significant differences in terms of the single-channel conductance of these channels were observed among the NaCl-unadapted, the NaSO-adapted and the Na100-adapted cells. These observations suggest that adaptation to salinity of tobacco cells in suspension results in reduced permeability of the K+ channels to both K+ and Na+ ions, without any change in the K+/Na+ selectivity and single-channel conductance of these channels.