title: Breaking the silence: functional expression of the two-pore-domain potassium channel THIK-2.
abstract: THIK-2 belongs to the 'silent' channels of the two-pore-domain potassium channel family. It is highly expressed in many nuclei of the brain but has so far resisted all attempts at functional expression. THIK-2 has a highly conserved 19-amino-acid region in its N terminus (residues 6-24 in the rat orthologue) that is missing in the closely related channel THIK-1. After deletion of this region (THIK-2(Δ6-24) mutant), functional expression of the channel was observed in Xenopus oocytes and in mammalian cell lines. The resulting potassium current showed outward rectification under physiological conditions and slight inward rectification with symmetrical high-K(+) solutions and could be inhibited by application of halothane or quinidine. Another THIK-2 mutant, in which the putative retention/retrieval signal RRR at positions 14-16 was replaced by AAA, produced a similar potassium current. Both mutants showed a distinct localisation to the surface membrane when tagged with green fluorescent protein and expressed in a mammalian cell line, whereas wild-type THIK-2 was mainly localised to the endoplasmic reticulum. These findings suggest that deletion of the retention/retrieval signal RRR enabled transport of THIK-2 channels to the surface membrane. Combining the mutation THIK-2(Δ6-24) with a mutation in the pore cavity (rat THIK-2(I158G)) gave rise to a 12-fold increase in current amplitude, most likely due to an increase in open probability. In conclusion, the characteristics of THIK-2 channels can be analysed in heterologous expression systems by using trafficking and/or gating mutants. The possible mechanisms that enable THIK-2 expression at the surface membrane in vivo remain to be determined.
authors.affiliation: Institute of Physiology and Pathophysiology, Marburg University, Deutschhausstr. 2, 35037, Marburg, Germany, vijay@staff.uni-marburg.de.
authors.forename: Vijay
authors.initials: V
authors.lastname: Renigunta
authors.forename: Xinle
authors.initials: X
authors.lastname: Zou
authors.forename: Stefan
authors.initials: S
authors.lastname: Kling
authors.forename: Günter
authors.initials: G
authors.lastname: Schlichthörl
authors.forename: Jürgen
authors.initials: J
authors.lastname: Daut
mesh_terms: D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D002522:Chlorocebus aethiops; D003412:Cricetulus; D006367:HeLa Cells; D006801:Humans; D009865:Oocytes; D018408:Patch-Clamp Techniques; D024683:Potassium Channels, Tandem Pore Domain / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology*; D051381:Rats; D014162:Transfection; D014982:Xenopus laevis
chemical_list: C430726:Kcnk12 protein, rat; D024683:Potassium Channels, Tandem Pore Domain