Emerging Concepts in Ion Channel Biophysics

Emerging Concepts in Ion Channel Biophysics

Poster Abstracts

42-POS Board 42 Mefloquine: a Local Anaesthetic Site Binder with a Unique Structure-activity Profile on the Mammalian Na + Channel Angel Islas 1,2 , Bertin Paiz-Candia 2 , Alfredo Sánchez-Solano 1 , Claudia Mancilla-Simbro 1 , Thomas Scior 2 , Lourdes Millan-Perez 3 , Eduardo M. Salinas-Stefanon 1 . 1 Laboratorio de Biofísica, Instituto de Fisiología, Universidad Autónoma de Puebla, Puebla, Puebla, Mexico, 2 Facultad de Ciencias Químicas, Universidad Autónoma de Puebla, Puebla, Mexico, 3 Centro de Química, Instituto de Ciencias, Universidad Autónoma de Puebla, Puebla, Puebla, Mexico. Mefloquine is a cation channel inhibitor, originally co-developed by the US Department of Defense to treat malaria. By combining site-directed mutagenesis, electrophysiology, molecular modelling, docking and Molecular Dynamics (MD), we were able to predict a loss and gain-of- function of the mefloquine-induced block of rat Nav1.4 channels. This antimalarial may occupy the local anaesthetic binding site (LABS) inasmuch as the mutant Phe1579A increased the IC50 by two-fold. All-atom MD combined with rigid-protein and induced-fit docking posits that (11S,12R)-mefloquine binds the rNav1.4 channel at a hydrophobic cavity that communicates the LABS with the selectivity filter, which coincides with the latest local anaesthetics binding mode, but differs in that this drugs binds above Phe1579, the side of which fluctuates from a proximal to a distal conformation from the channel permeation pathway during the simulations. Although, like most local anaesthetics, mefloquine showed used-dependent increase in block, the current rundown did not increased at escalating frequencies. This compound prominently accelerated peak current decay, with no effect on recovery from inactivation and the co-expression of the β1 subunit, which significantly accelerates the inactivation and recovery kinetics of most mammalian Na+ channels, increased the IC50 of mefloquine from 67 to 128μM. Taken together these results suggest that, in contrast to the hallmark action mechanism of local anaesthetics, mefloquine does not stabilize Na+ channels in the inactivated state, but it preferentially binds activated channels facilitating inactivation. However the apparent drug affinity to inactivated channels (Ki), derived by differences in the steady-state inactivation, suggest drug binding preference to inactivated channels than to channels in the resting state, i.e Ki=9.6μM, if IC50≈Kr, (IC50=67μM).

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