Time- and Voltage-Dependent Components of Kv4.3 Inactivation

Abstract

Kv4.3 inactivation is a complex multiexponential process, which can occur from both closed and open states. The fast component of inactivation is modulated by the N-terminus, but the mechanisms mediating the other components of inactivation are controversial. We studied inactivation of Kv4.3 expressed in Xenopus laevis oocytes, using the two-electrode voltage-clamp technique. Inactivation during 2000 ms pulses at potentials positive to the activation threshold was described by three exponents (46 +/- 3, 152 +/- 13, and 930 +/- 50 ms at +50 mV, n = 7) whereas closed-state inactivation (at potentials below threshold) was described by two exponents (1079 +/- 119 and 3719 +/- 307 ms at -40 mV, n = 9). The fast component of open-state inactivation was dominant at potentials positive to -20 mV. Negative to -30 mV, the intermediate and slow components dominated inactivation. Inactivation properties were dependent on pulse duration. Recovery from inactivation was strongly dependent on voltage and pulse duration. We developed an 11-state Markov model of Kv4.3 gating that incorporated a direct transition from the open-inactivated state to the closed-inactivated state. Simulations with this model reproduced open- and closed-state inactivation, isochronal inactivation relationships, and reopening currents. Our data suggest that inactivation can proceed primarily from the open state and that multiple inactivation components can be identified.

Inhibition of Kv4.3 by genistein via a tyrosine phosphorylation-independent mechanism

“…Our results indicate that the affinity of Kv4.3 for genistein is 100 times greater for the inactivated state than for the closed state. Kv4.3 channels can be inactivated from either the open or closed states, but inactivation most frequently occurs from the closed state without activation (37). Accordingly, genistein caused a marked acceleration of the closed-state inactivation of Kv4.3.…”

“…Previous studies have shown that Kv4.3 channels are predominantly inactivated from the closed state without opening in the subthreshold voltage range (37). We tested the effect of genistein on the kinetics of closed-state inactivation.…”

Heteropoda Toxin 2 Interaction with Kv4.3 and Kv4.1 Reveals Differences in Gating Modification

“…Two-Electrode Voltage-Clamp Technique. Currents were measured in oocytes using a two-microelectrode Dagan CA-1B amplifier as described previously (Wang et al, 2004;Wang et al, 2005). Electrodes were filled with 3 M KCl.…”

W-7 modulates Kv4.3: pore block and Ca2+-calmodulin inhibition

“…We used a 1,000-ms depolarization pulse, which only results in a biexponential inactivation time course (72). During exposure to 85 M W-7, 1 and 2 decreased from 47.1 Ϯ 2.7 and 322.4 Ϯ 27.1 ms to 24.8 Ϯ 4.2 and 123.8 Ϯ 7.0 ms, respectively.…”

“…8). The kinetics of closed-state inactivation were evaluated using subthreshold depolarizing pulses (9,10,72). These protocols consisted of four pulses: P1 from Ϫ100 to ϩ40 mV (800 ms); P2 to Ϫ100 mV (5 s); P3 to variable voltages and durations (from Ϫ80 to Ϫ40 mV and from 800 ms to 14.4 s); and P4 to ϩ40 mV (800 ms), followed by a return to a holding potential of Ϫ100 mV.…”