Aluminum activates an anion channel in the apical cells of wheat roots

We describe an anion channel in the plasmalemma of protoplasts isolated from wheat (Triticum aestivum L.) roots that is activated by aluminum (Al(3+)). In the whole-cell configuration, addition of 20-50 micromolar AlCl3 to the external solution depolarized the membrane and activated an inward current that could remain active for more than 60 min. The activation by Al(3+) was rapid in 20% of protoplasts examined, whereas in another 30% a delay of more than 10 min occurred after Al(3+) was added. Once the current was activated, changing the external Cl- concentration shifted the membrane reversal potential with E(Cl) showing that the channel is more selective for anions than cations (Ca(2+), K(+), tetraethylammonium(+)). The channel could be activated by Al(3+), but not by La(3+), and was observed in protoplasts isolated from the root apex but not in protoplasts isolated from mature root tissue. The anion channel antagonist niflumate inhibited the current in whole cell measurements by 83% at 100 micromolar. Outside-out patch recordings revealed a multistate channel with single-channel conductances of between 27 and 66 pS