The K_2P channel TREK-1 is regulated by diverse physical and chemical stimuli and several protein interaction partners. Recently we have identified the enzyme heme oxygenase 2 (HO-2) as a possible interaction partner of TREK-1. Functional interaction was demonstrated by voltage-clamp measurements showing an increase in TREK-1 currents after co-expression with HO-2 in Xenopus oocytes.

HO-2 catalyses the breakdown of heme into biliverdin, iron and carbon monoxide (CO). For this process heme has to be bound to histidine (H) at position 45 in HO-2. Mutation of H45 to asparagine (N) prevents the binding of heme and renders the hemoxygenase inactive. Co-expression of TREK-1 and HO-2-H45N in oocytes did not produce an increase in current amplitude.

To study the influence of the heme degradation product CO on TREK-1 the CO-donor CORM-2 was applied, which caused an increase in TREK-1 currents in both oocytes and HEK 293 cells. Mutation of two serine (S) residues of TREK-1 at positions 344 (PKA phosphorylation site) and 362 (PKG phosphorylation site) produced different results after application of CORM-2: while mutation of S344 drastically reduced the stimulatory effect of CO on the channel, the mutation of S362 did not modulate the effect of CO. As it is well established that nitric oxide (NO) activates TREK-1 currents via the PKG signaling pathway we applied a NO-donor (SNP/DTT) on TREK-1 wt and the S344 and S362 mutants. We found that the stimulatory effect of NO on TREK-1 was abolished when S362 was mutated, but mutation of S344 had no influence on the NO effect.

Our results suggest that (1) interaction between HO-2 and TREK-1 leads to activation of the channel via locally produced CO; (2) the stimulatory effects of CO and NO on TREK-1 are mediated by different signalling pathways: the CO effect is mediated by S344 and the NO effect is mediated by S362.