TASK-5, a new member of the tandem-pore K(+) channel family.

TASKs are members of the recently identified K(+) channel family (KCNKx). Four TASKs (TASK1-4) identified so far form functional K(+) channels and encode background K(+) channels in various cell types. Recently, another member (TASK-5) was identified in the human genome. We cloned it and studied its tissue expression and functional properties. TASK-5 shares 51% amino acid identity with TASK-1 and TASK-3. Northern blot analysis showed that TASK-4 mRNA was expressed primarily in the adrenal gland and pancreas. Single nucleotide polymorphism (SNP) was found at amino acid position 95 that normally forms part of the K(+) channel selectivity filter. Neither form of TASK-5 showed channel activity when transfected in COS-7 cells. Exchange of C-termini of TASK-3 and TASK-5 failed to generate whole-cell currents. Thus, TASK-5 is a new member of the tandem-pore K(+) channel family but does not produce a functional plasma membrane K(+) current by itself.