Effects of La3+ on outward K+ channels at plasma membrane in Vicia mesophyll cells

The effects of La3+ on outward K+ channels at plasma membrane in vicia mesophyll cells were studied by using the whole-cell patch-clamp recording mode. It was shown that La3+ on both sides of plasma membrane blocked outward K+ currents in a concentration-dependent manner. The dose response was fitted by the Michalis-Menten relationship characterized by an inhibitory constant K-i of (76.59 +/- 9. 28) mumol/L(outside membrane) and (5.80 +/- 0.62) x 10(-15) mol/L(inside membrane) respectively, suggesting that intra-cellular La3+ had a stronger inhibitory effect on outward K+ currents than extra-cellular La3+ did. Since K+ remains the dominant osmoticum in mesophyll cells, the inhibition of outward K+ currents by La3+ may contribute greatly to preventing the K+ loss and promoting turgor maintenance. These results implied that rare earth elements might have potential practical values in regulating plant water status and strengthening plant drought endurance.