ATP-Dependent Regulation of an Anion Channel at the Plasma Membrane of Protoplasts from Epidermal Cells of Arabidopsis Hypocotyls

Although Arabidopsis is the object of many genetic and molecular biology investigations, relatively few studies deal with regulation of its transmembrane ion exchanges. To clarify the role of ion transport in plant development, organ-and tissue-specific ion channels must be studied. We identified a voltage-dependent anion channel in epidermal cells of Arabidopsis hypocotyls, thus providing a new example of the occurrence of voltage-dependent anion channels in a specific plant cell type distinct from the stomatal guard cell. The Arabidopsis hypocotyl anion channel is able to function under two modes characterized by different voltage dependences and different kinetic behaviors. This switch between a fast and a slow mode is controlled by ATP. In the presence of intracellular ATP (fast mode), the channels are closed at resting potentials, and whole-cell currents activate upon depolarization. After activation, the anion current deactivates rapidly and more and more completely at potentials negative to the peak. In the absence of ATP, the current switches from this fast mode to a mode characterized by a slow and incomplete deactivation at resting potentials. In addition, the whole-cell currents can be correlated with the activity of single channels. In the outside-out configuration, the presence of ATP modulates the mean lifetimes of the open and closed states of the channel at hyperpolarized potentials, thus controlling its open probability. The fact that ATP-dependent voltage regulation was observed in both whole-cell and outside-out configurations suggests that a single type of anion channel can switch between two modes with distinct functional properties.