Transplanting the N-terminus from Kv1.4 to Kv1.1 generates an inwardly rectifying K+ channel

A chimeric channel, 4N/1, was generated from two outwardly rectifying K+ channels by linking the N-terminal cytoplasmic domain of hKv1.4 (N terminus ball and chain of hKv1.4) with the transmembrane body of hKv1.1 (delta78N1 construct of hKv1.1). The recombinant channel has properties similar to the six transmembrane inward rectifiers and opens on hyperpolarization with a threshold of activation at -90 mV. Outward currents are seen on depolarization provided the channel is first exposed to a hyperpolarizing pulse of -100 mV or more. Hyperpolarization at and beyond -130 mV provides evidence of channel deactivation. Delta78N1 does not show inward currents on hyperpolarization but does open on depolarizing from -80 mV with characteristics similar to native hKv1.1. The outward currents seen in both delta78N1 and 4N/1 inactivate slowly at rates consistent with C-type inactivation. The inward rectification of the 4N/1 chimera is consistent with the inactivation gating mechanism. This implies that the addition of the N-terminus from hKv1.4 to hKv1.1 shifts channel activation to hyperpolarizing potentials. These results suggest a mechanism involving the N-terminal cytoplasmic domain for conversion of outward rectifiers to inward rectifiers.