An essential function of phosphatidylinositol phosphates in activation of plant shaker-type K+ channels

A prominent regulatory property of plant shaker-type Kþ channels is the 'rundown' that causes channel closure upon membrane excision from the cell, implicating intracellular factor(s)in maintaining channel activity. One such factor has been identified as hydrolysable ATP-Mg although the mechanism for ATP function remains unknown. Here we report identification of phosphatidylinositol (PI)phosphates (PIPs)as essential regulators for the voltage-dependent and -independent activation of plant shaker-type channels such as SKOR, an outward rectifying Kþ channel. Inhibition of PI kinase activity abolished the function of ATP-Mg in restoration of rundown channel activity, demonstrating that PIPs production by PI kinases and ATP-Mg underlies ATPinduced activation of the rundown channel. We also identified aluminum block as a common feature of the plant shaker-type channels and provided evidence that aluminum block of these channels may result from Al interaction with PIPs.