Trafficking of the plant potassium inward rectifier KAT1 in guard cell protoplasts of Vicia faba

Trafficking of K+ inward (K-in(+)) rectifying channels was analyzed in guard cells of Vicia faba transfected with the K-in(+) rectifier from Arabidopsis thaliana KAT1 fused to the green fluorescent protein (GFP). Confocal images and whole-cell patch-clamp measurements confirmed the incorporation of active KAT1 channels into the plasma membrane of transfected guard cell protoplasts. The K-in(+) rectifier current density of the plasma membrane was much larger in transfected protoplasts than in wild-type (wt) protoplasts. This shows a coupling between K+ channel synthesis and incorporation of the channel into the plasma membrane. Pressure-driven increase and decrease in surface area led to the incorporation and removal of vesicular membrane carrying active K-in(+) rectifier in wt and transfected protoplasts. These vesicular membranes revealed a higher channel density than the plasma membrane, suggesting that K-in(+) rectifier remains in clusters during trafficking to and from the plasma membrane. The observed results can be explained by a model illustrating that vesicles of a pre-plasma membrane pool carry K+ channels preferentially in clusters during constitutive and pressure-driven exo- and endocytosis.