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 2000ms pulses at potentials positive to the activation threshold was described by three exponents (46±3, 152±13, and 930±50ms at +50mV, n=7) whereas closed-state inactivation (at potentials below threshold) was described by two exponents (1079±119 and 3719±307ms at −40mV, n=9). The fast component of open-state inactivation was dominant at potentials positive to −20mV. Negative to −30mV, 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.