Functional and biochemical evidence for G-protein-gated inwardly rectifying K+ (GIRK) channels composed of GIRK2 and GIRK3

G-protein-gated inwardly rectifying K+ (GIRK) channels are widely expressed in the brain and are activated by at least eight different neurotransmitte rs. As Kt channels, they drive the transmembrane potential toward E-K when open and thus dampen neuronal excitability. There are four mammalian GIRK s ubunits (GIRK1-4 or Kir 3.1-4), with GIRK1 being the most unique of the fou r by possessing a long carboxyl-terminal tail. Early studies suggested that GIRK1 was an integral component of native GIRK channels. However, more rec ent data indicate that native channels can be either homo- or heterotetrame ric complexes composed of several GIRK subunit combinations. The functional implications of subunit composition are poorly understood at present. The purpose of this study was to examine the functional and biochemical propert ies of GIRK channels formed by the co-assembly of GIRK2 and GIRK3, the most abundant GIRK subunits found in the mammalian brain. To examine the proper ties of a channel composed of these two subunits, we co-transfected GIRK2 a nd GIRK3 in CHO-K1 cells and assayed the cells for channel activity by patc h clamp. The most significant difference between the putative GIRK2/GIRK3 h eteromultimeric channel and GIRK1/GIRKx channels at the single channel leve l was an similar to5-fold lower sensitivity to activation by G beta gamma. Complexes containing only GIRK2 and GIRK3 could be immunoprecipitated from transfected cells and could be purified from native brain tissue. These dat a indicate that functional GIRK channels composed of GIRK2 and GIRK3 subuni ts exist in brain.