Sulfate is both a substrate and an activator of the voltage-dependent anion channel of Arabidopsis hypocotyl cells

On the basis of the anion content of in vitro-cultured Arabidopsis plantlets, we explored the selectivity of the voltage-dependent anion channel of the plasma membrane of hypocotyl cells. In the whole-cell configuration, substitution of cytosolic Cl- by different anions led to the following sequence of relative permeabilities: NO3- (2.6) greater than or equal to SO42- (2.0) > Cl- (1.0) > HCO3- (0.8) much greater than malate(2-)(0.03). Large whole-cell currents were measured for NO3- and SO42-, about five to six times higher than the equivalent Cl- currents. Since SO42- is usually considered to be a weakly permeant or non-permeant ion, the components of the large whole-cell current were explored in more detail. Aside from its permeation through the channel with a unitary conductance, about two-thirds that of Cl-, SO42- had a regulatory effect on channel activity by preventing the run-down of the anion current both in the whole-cell and the outside-out configuration, increasing markedly the whole-cell current. The fact that the voltage-dependent plasma membrane anion channel of hypocotyl cells can mediate large NO3- and SO42- currents and is regulated by nucleotides favors the idea that this anion channel can contribute to the cellular homeostasis of important metabolized anions.