Internal aluminum block of plant inward K+ channels

Aluminum (Al) inhibits inward K+ channels (K-in) in both root hair and guar d cells, which accounts for at least part of the Al toxicity in plants. To understand the mechanism of Al-induced K-in inhibition, we performed patch clamp analyses on K-in in guard cells and on KAT1 channels expressed in Xen opus oocytes. Our results show that Al inhibits plant K-in by blocking the channels at the cytoplasmic side of the plasma membrane. In guard cells, si ngle-channel recording revealed that Al inhibition of K-in occurred only up on internal exposure. Using both "giant patch" recording and single-channel analyses, we found that Al reduced KAT1 open probability and changed its a ctivation kinetics through an internal membrane-delimited mechanism. We als o provide evidence that a Ca2+ channel-like pathway that is sensitive to an tagonists verapamil and La3+ mediates Al entry across the plasma membrane. We conclude that Al enters plant cells through a Ca2+ channel-like pathway and inhibits K+ uptake by internally blocking K-in.