Sulfate Is Both a Substrate and an Activator of the Voltage-Dependent Anion Channel of Arabidopsis Hypocotyl Cells

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Abstract
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) ≥ SO42− (2.0) > Cl−(1.0) > HCO3− (0.8) ≫ malate2− (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.