SUBUNIT INTERACTIONS IN THE ASSEMBLY OF NEURONAL KIR3.0 INWARDLY RECTIFYING K+ CHANNELS

Cardiac G protein-activated Kir (GIRK) channels may assemble as hetero tetrameric polypeptides from two subunits, Kir3.1 and Kir3.4. For a fu nctional comparison with native channels in the CNS we investigated al l possible combinations of heteromeric channel formation from brain Ki r3.1, Kir3.2, Kir3.3, and Kir3.4 subunits in mRNA-injected Xenopus ooc ytes. Analysis of macroscopic current amplitudes and channel gating ki netics indicated that individual subunits or combinations of Kir3.2, K ir3.3, and Kir3.4 formed functional channels ineffectively. Each of th ese subunits gave rise to prominent currents with distinct characteris tics only in the presence of Kir3.1 subunits. Functional expression of concatemeric constructs between Kir3.1 and Kir3.2/3.4 subunits as wel l as coimmunoprecipitations with subunit-specific antibodies confirmed heteromeric channel formation. Mutational swapping between subunits o f a single pore loop residue (Kir3.1(F137S); Kir3.3(S114F); a phenylal anine confers slow channel gating in Kir3.1 subunits) revealed that Ki r3.1 subunits are an important constituent for native heteromeric chan nels and dominate their functional properties. However, homomeric chan nels from Kir3.1 subunits in vivo may not exist due to the spatial con flict of bulky phenylalanines in the pore structure.