Slowing of Instantaneous Inactivation Causes Macroscopic Current Decay in Kv7.1 Alanine Mutants

Abstract

Alanine scanning mutagenesis in Kv7.1 S4-S5 linker and the pore region revealed mutant channels with fast current decay at permanent depolarizing pulses above 10mV. It has been previously shown that such a macroscopic inactivation of many Kv7.1 pore mutants occurs in parallel to instantaneous inactivation of Kv7.1 channel. We have chosen four mutant channels I268A, G269A, F339A and F340A with most pronounced current decays to investigate the molecular mechanism underling decay process. Inactivation of these channels could not be explained by intracellular Na+ block reported earlier for Kv7.1 wild type channel. The fast current decay kinetics significantly changed neither by varying the extracellular K+ concentration nor by replacement of the K+ with equimolar Rb+. Recovery from inactivation showed fast and slow components. The slow component was accelerated at high extracellular K+ conditions, whereas the fast component did not change significantly. Our data suggest that instantaneous inactivation of wild type Kv7.1 channel markedly slowed by above mentioned alanine mutations resulting in macroscopic decay of current during prolonged depolarization.