Calcium-dependent activation of TREK-1 and TREK-2 background potassium channels by calcineurin

TREK-1 (K_2P2.1) and TREK-2 (K_2P10.1) background K⁺ channels are widely expressed determinants of cellular excitability. We examined the regulation of TREK channels by the increase of cytoplasmic calcium concentration in Xenopus oocytes. Extracellular application of ionomycin, as well as the microinjection of inositol 1,4,5-trisphosphate (IP₃), evoked TREK-1 activation, whereas the microinjection of EGTA prevented the effect. TRAAK (K_2P4.1) was not affected, whereas TREK-2 was activated by ionomycin in the presence of ML-335 K_2P activator compound. Cyclosporin A and FK506, specific inhibitors of the calcium/calmodulin-dependent protein phosphatase (calcineurin), abrogated the activation of TREK channels by ionomycin. Coexpression of a constitutively active form of calcineurin with TREK-1 increased the background K⁺ current, but FK506 restored the basal channel activity. Mutations of TREK-1 phosphorylation sites (S300A/S333A) eliminated the response to ionomycin. Coexpression of the known interaction partner AKAP5 (AKAP79/AKAP150) with TREK-1 significantly enhanced the calcium-dependent activation. The wild-type anchoring protein induced higher TREK activation than a dominant negative AKAP5 construct carrying mutations in the PXIXIT-like calcineurin binding site. In conclusion, TREK-1 and TREK-2 are regulated in a calcium-dependent manner, in addition to the previously described TRESK (K_2P18.1), however, TREK channels are activated by calcineurin anchored to AKAP5.