Inward Rectifying K+ Channels in the Plasma Membrane of Arabidopsis thaliana

Ion channels in the plasma membrane of protoplasts isolated from cultured cells of Arabidopsis thaliana were studied by means of the patch-clamp technique applied in the whole-cell configuration. In some protoplasts, depolarizing pulses and, in other protoplasts, hyperpolarizing pulses elicited time-dependent currents; both kinds of current were only rarely observed in the same protoplast. The hyperpolarization-activated inward rectifying currents, the focus of this paper, appeared to be due to the relatively slow opening of channels (activation time constant = 150 to 300 milliseconds), which closed at positive potentials. The reversal potential of this current, measured in the presence of different ion concentrations (symmetrical or asymmetrical K(+) and Cl(-) or gluconate), was always close to the electrochemical equilibrium potential of K(+). The currents were inhibited by 10 millimolar tetraethylammonium, a K(+) channel blocker. These data show that the hyperpolarization-activated currents flow through K(+) channels, which can provide a pathway for the passive diffusion of K(+) down its electrochemical gradient.