FUNCTIONAL EXPRESSION OF THE PLANT K+ CHANNEL KAT1 IN INSECT CELLS

Following the biophysical analysis of plant K+ channels in their natur al environment, three members from the green branch of the evolutionar y tree of life KAT1, AKT1 and KST1 have recently been identified on th e molecular level, Among them, we focused on the expression and charac terization of the Arabopsis thaliana K+ channel KAT1 in the insect cel l line Sf9, The infection of Sf9 cells with KAT1-recombinant baculovir us resulted in functional expression of KAT1 channels, which was monit ored by inward-rectifying, K+-selective (impermeable to Na+ and even N H4+) ionic conductance in whole-cell patch-clamp recordings, A voltage threshold as low as -60 to -80 mV for voltage activation compared to other plant inward rectifiers in vivo, and to in vitro expression of K AT1 in Xenopus oocytes or yeast, may be indicative for channel modulat ion by the expression system, A rise in cytoplasmic Ca2+ concentration (up to 1 mM), a regulator of the inward rectifier in Vicia faba guard cells, did not modify the voltage dependence of KAT1 in Sf9 cells, Th e access to channel function on one side and channel protein on the ot her make Sf9 cells a suitable heterologous system for studies on the b iophysical properties, post-translational modification and assembly of a green inward rectifier.