From frog oocytes to mammalian cells: substantial differences in modulation of NaV1.4 channel slow kinetic behaviour by the β1 subunit

Background Voltage gated sodium channels consist of an α subunit and several modulating β subunits. Upon depolarization, the α subunit first opens and then enters into different types of inactivated states. When expressed in mammalian cells, the β1 subunit has been shown to modulate the kinetics of fast inactivation. Here, we tested whether a very stable inactivated state, which we refer to as ultra-slow inactivation (Ius), is subject to modulation by the β1 subunit of the sodium channel. Previously, we showed that NaV1.4 channels, containing the mutation K1237E in the selectivity filter, had enhanced entry into Ius when expressed in Xenopus oocytes. Coexpression of the β1 subunit in this system had no effect on Ius. However, the kinetic behaviour of NaV1.4 may vary between the Xenopus oocyte system and mammalian expression systems. As both systems are widely used in ion channel research, it appeared of interest to evaluate the kinetic effect of coexpression of β1 in a mammalian expression system. Therefore, we tested whether Ius could be reproduced in TSA201 mammalian cells and whether it is subject to modulation by the β1 subunit in this system.