Received for publication December 5, 2007.
Revised January 18, 2008.
Accepted for publication January 22, 2008.

Structural basis for ether-a-go-go-related gene K⁺ channel subtype-dependent activation by niflumic acid

Abstract

Niflumic acid (2-((3-(trifluoromethyl)phenyl)amino)-3-pyridinecarboxylic acid, NFA) is a nonsteroidal anti-inflammatory drug that also blocks or modulates the gating of a wide spectrum of ion channels. Here we investigated the mechanism of channel activation by NFA on ether-a-go-go-related gene (ERG) K⁺ channel subtypes expressed in Xenopus oocytes using two-electrode voltage clamp techniques. NFA acted from the extracellular side of the membrane to differentially enhance ERG channel currents independent of channel state. At 1 mM, NFA shifted the half-point for activation by -6, -18 and -11 mV for ERG1, ERG2 and ERG3 channels respectively. The half-point for channel inactivation was shifted by +5 to +9 mV by NFA. The structural basis for the ERG subtype-specific response to NFA was explored with chimeric channels and site-directed mutagenesis. The molecular determinants of enhanced sensitivity of ERG2 channels to NFA were isolated to an Arg and a Thr triplet in the extracellular S3-S4 linker.

Key words: Ion transporters (SERCA, Na/K ATPase, CFTR), Structure-activity relationships and modeling, Mutagenesis/Chimeric approaches