Effect of Counter Ions on the Transport Current Across Membranes Containing KAT1 Potassium Channel

Ion transports from one aqueous phase (W1) to another (W2) across bilayer lipid membranes (BLM) containing KAT1 potassium channel were investigated by recording current fluctuations. KAT1 channel is a voltage-gated K+ channel from Arabidopsis thaliana and has been suggested to have a key role in stomatal opening by osmoregulation in guard cells. Although KAT1 channel is a K+-specific transporter, the species of the counter anions significantly affected the level of the single channel current, suggesting that KAT1 also transported these anions. When various potassium salts were used as electrolytes, the single channel conductance decreased with an increase of the ionic radius of the coexisting anions except for F-. This indicates the existence of selective permeation for anions, but the anion-selectivity is less noticeable than the cation-selectivity.