Since their first isolation, the 2P potassium channels have posed a fascinating conundrum. On the one hand, they are always open, leading to the impression that they are leak channels that “merely” set up the resting membrane potential. On the other hand, they are regulated by a very large number of signaling systems (including polyunsaturated fatty acids, phosphoinositides, pH, GPCRs, protein kinases, temperature, and mechanical

force), giving the impression that they are a vital hub of neuronal control. Adding to the mystery, their genetic knockout often has only subtle effects, although in some cases intriguing specificity has emerged for different family members, for example in poly-unsaturated-fatty-acid-mediated neuroprotection, selleck products anesthesia, pain perception, and for a possible role in the treatment of depression (Heurteaux et al., 2004, Heurteaux et al., 2006, Mazella et al., 2010 and Noël et al., 2009). Attempts at definitive determination of function have been hampered by a lack of specific, reversible pharmacological agents. Our TREK1-PCS paves the way for solving this pharmacological problem, since the 2P potassium

channels show similar block by external quaternary ammonium moieties and this is the blocking ligand of the MAQ photoswitch. In the present case of TREK1, the Shaker channel served as a successful guide for where to introduce the MAQ attachment site, even though, outside of the pore region, the 2P potassium channels have strongly diverged from the Shaker-type Kv channels. Our Selleckchem BVD 523 screen for MAQ attachment sites in the P regions of TREK1 provided

one preferred position, at which block is relieved in the dark, conferred under 380 nm illumination (cis state), and relieved under 500 nm illumination (trans state). As with other azobenzene PTLs, on and off gating can be repeated many times without loss of efficacy and the switch is bistable, persisting for long periods without illumination in the higher energy cis-blocked state, but available for a rapid return to trans with light. Interestingly, in TREK1 we found differences in photoblock by MAQ when it was attached to homologous positions in the Resminostat first (P1) pore region versus the second (P2) pore region. Recently obtained structures of the pore of 2P-potassium channels, TRAAK ( Brohawn et al., 2012) and TWIK1 ( Miller and Long, 2012), have shown that the two-fold symmetry converges to an essential four-fold symmetric pore helix and selectivity filter. However, the regions homologous to our cysteine attachment sites in TREK1 are not seen in these crystal structures. Our finding that MAQ attachment to homologous positions in the P1 and P2 of TREK1 yield different blocking characteristics suggests that these portions of the pore region are not four-fold symmetric. The tandem coupling of pairs of subunits that characterizes 2P channels may serve to constrain this asymmetry.