Ca²⁺ regulation of outward rectifying K⁺ channel in the plasma membrane of tobacco cultured cells in suspension: A role of the K⁺ channel in mitigation of salt-stress effects by external Ca²⁺

The patch-clamp technique was used to study effect of the Ca²⁺ on K⁺ channels in the plasma membrane of protoplasts isolated from tobacco (Nicotiana tabacum L., cv. Bright Yellow) cultured cells in suspension. The outward rectifying whole-cell K⁺ currents were not affected by intracellular Ca²⁺, but they were reduced with increasing extracellular Ca²⁺. Neither extracellular nor intracellular Ca²⁺ affected the permeability ratios (P(K)+/P(Na)+) of the plasma membrane. These results suggest that the inhibition of outward-rectifying K⁺ channels by extracellular Ca²⁺ may partially contribute towards the mitigation of detrimental effects of salinity on growth by extracellular Ca²⁺.