AMINO TERMINAL-DEPENDENT GATING OF THE POTASSIUM CHANNEL RAT EAG IS COMPENSATED BY A MUTATION IN THE S4 SEGMENT

1. Rat eag potassium channels (r-eag) were expressed in Xenopus oocyte s. They gave rise to delayed rectifying K+ currents with a strong Cole -Moore effect. 2. Deletions in the N-terminal structure of r-eag eithe r shifted the activation threshold to more negative potentials and slo wed the activation kinetics (Delta 2-190, Delta 2-12 and Delta 7-12) o r resulted in a shift to more positive potentials and faster activatio n kinetics (Delta 150-162). 3. The impact of the deletion Delta 7-12 w as investigated in more detail: it almost abolished the Cole-Moore eff ect and markedly slowed down channel deactivation. 4. Unlike wild-type channels, the deletion mutants Delta 7-1.2 exhibited a rapid inactiva tion which, in combination with the slow deactivation, resulted in cur rent characteristics which were similar to those of the related potass ium channel HERG. 5. Both the slowing of deactivation and the inactiva tion induced by the deletion Delta 7-12 were compensated by a single h istidine-to-arginine change in the S4 segment, while this mutation (H3 43R) only had minor effects on the gating kinetics of the full-length r-eag channel. 6. These results demonstrate a functional role of the N -terminus in the voltage-dependent gating of potassium channels which is presumably mediated by an interaction of the N-terminal protein str ucture with the S4 motif during the gating process.