Figure 1. Effects of concatenation and I470V mutations on inactivation.

(a) Shaker homotetramer. Cartoon represents a Shaker homotetramer channel having four inactivation gates (top) with a representative K⁺ current in response to a voltage step to +60 mV from a holding potential of −80 mV displayed below. Red line overlaying the trace represents a fit of the inactivation process to a Markov kinetic model parameterized by the time constants k_on and k_off. Average values were: k_on=430±70 s⁻¹; k_off=21±2 s⁻¹. Horizontal bar for all panels: 10 ms; Vertical bar: 100 pA. (n=5 patches, 43 traces). (b) Shaker concatemer having one inactivation gate. Cartoon (top) with a representative K⁺ current shown below. Best fit parameter values were: k_on=108±21 s⁻¹ and k_off=40±9 s⁻¹. We noticed that k_off of wild-type concatemer was ~ × 2 faster than Shaker homotetramer. Vertical bar: 300 pA. (n=7 patches, 68 traces). (c) Shaker concatemer having one inactivation gate and four subunits with I470V mutation. Cartoon (top) with a representative K⁺ current shown below. Best fit parameter values were: k_on=90±3 s⁻¹; k_off=163±66 s⁻¹. Vertical bar: 100 pA. (n=10 patches, 114 traces).