Effects of ionic strength on gating and permeation of TREK-2 K2P channels.

Linus J Conrad,Stephen J Tucker,Peter Proks,Jorge Arreola

doi:10.1371/journal.pone.0258275

Abstract

In addition to the classical voltage-dependent behavior mediated by the voltage-sensing-domains (VSD) of ion channels, a growing number of voltage-dependent gating behaviors are being described in channels that lack canonical VSDs. A common thread in their mechanism of action is the contribution of the permeating ion to this voltage sensing process. The polymodal K2P K+ channel, TREK2 responds to membrane voltage through a gating process mediated by the interaction of K+ with its selectivity filter. Recently, we found that this action can be modulated by small molecule agonists (e.g. BL1249) which appear to have an electrostatic influence on K+ binding within the inner cavity and produce an increase in the single-channel conductance of TREK-2 channels. Here, we directly probed this K+-dependent gating process by recording both macroscopic and single-channel currents of TREK-2 in the presence of high concentrations of internal K+. Surprisingly we found TREK-2 is inhibited by high internal K+ concentrations and that this is mediated by the concomitant increase in ionic-strength. However, we were still able to determine that the increase in single channel conductance in the presence of BL1249 was blunted in high ionic-strength, whilst its activatory effect (on channel open probability) persisted. These effects are consistent with an electrostatic mechanism of action of negatively charged activators such as BL1249 on permeation, but also suggest that their influence on channel gating is complex.

Highlights

K2P-channels are involved in diverse physiological processes such as the perception of pain, mood [1, 2] and many other signaling pathways [3]
We found that BL1249 can activate TREK-2 in high [K+int] without increasing γ, a result that is consistent with the proposed electrostatic mechanism of action of negatively charged activators
If BL1249 activates TREK channels primarily via an increase in K+ occupancy of the filter, its effects on both γ and Po should both be masked in high [K+int]. Such concentration-dependent masking of electrostatic effects on γ have been well established in other K+ channels such as the BK and shaker channels [30, 31]

Summary

Introduction

K2P-channels are involved in diverse physiological processes such as the perception of pain, mood [1, 2] and many other signaling pathways [3]. They are often described as ‘background’ or ‘leak’ channels, many members of the family display prominent voltage-dependent behavior [4,5,6] and their activity can be regulated by a diverse array of physical and chemical stimuli [3]. K2P channels do not contain a classical voltage-sensing-domain (VSD) and most, including the subfamily of mechanically-gated K2Ps (TREK/TRAAK), lack an internal bundle-crossing gate making the selectivity filter (SF) the principal gate in these channels [7, 8]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Methods

Results

Conclusion