Functional interaction between KChIP1 and GFP-fused Kv4.3L co-expressed in HEK293 cells

The trafficking and electrophysiological characteristics of Kv4 subfamily are regulated by K+-channel-interacting proteins (KChIPs), which bind to the N-terminus of Kv4. We examined in HEK293 expression system whether the fusion of a green fluorescence protein (GFP) with Kv4.3L at the N-terminus would affect the functional interaction of KChIP1 with Kv4.3L. GFP-fused Kv4.3L showed A-type K+ current (I(A)) with significantly slower recovery from inactivation (tau=218 and 496 ms) and much lower density than those of original Kv4.3L expressed in HEK293 cells. The co-expression of KChIP1 with Kv4.3L strikingly increased the density of I(A) and hastened the recovery from inactivation (tau=133 ms). Surprisingly, co-expression of KChIP1 with GFP-fused Kv4.3L markedly enhanced the current density and hastened the recovery (tau=135 ms), just as the co-expression of KChIP1 with Kv4.3L did. In conclusion, the fusion of GFP to the N-terminus of Kv4.3L per se changed the channel kinetics but did not affect the functional interaction of KChIP1 with Kv4.3L at all. The trafficking of Kv4.3L by KChIP1 to the cell membrane was visualized with GFP fusion to the N-terminus without any significant modification of changes in channel kinetics and density.