Abstract
Little is known about the effect of lead on the activity of the vacuolar K(+) channels. Here, the patch-clamp technique was used to compare the impact of lead (PbCl(2)) on the slow-activating (SV) and fast-activating (FV) vacuolar channels. It was revealed that, under symmetrical 100-mM K(+), the macroscopic currents of the SV channels exhibited a typical slow activation and a strong outward rectification of the steady-state currents, while the macroscopic currents of the FV channels displayed instantaneous currents, which, at the positive potentials, were about three-fold greater compared to the one at the negative potentials. When PbCl(2) was added to the bath solution at a final concentration of 100 µM, it decreased the macroscopic outward currents of both channels but did not change the inward currents. The single-channel recordings demonstrated that cytosolic lead causes this macroscopic effect by a decrease of the single-channel conductance and decreases the channel open probability. We propose that cytosolic lead reduces the current flowing through the SV and FV channels, which causes a decrease of the K(+) fluxes from the cytosol to the vacuole. This finding may, at least in part, explain the mechanism by which cytosolic Pb(2+) reduces the growth of plant cells.