We began by comparing the functional properties of GIRK2a and GIRK2c expressed in mammalian (HEK) cells. As most neuronal GIRK channels are thought to be GIRK1/GIRK2 heteromers23, 24, HEK cells were transfected with GIRK1 and either GIRK2a or GIRK2c, along with the GABAB receptor (GABABR) subunits, GABABR1 and GABABR2. Whole-cell currents evoked by rapid bath application of the GABABR agonist baclofen (100 μM) were measured (Fig. 1A). While no response to baclofen was seen with expression of GABABR alone, cells expressing GABABR and either GIRK1/GIRK2a or GIRK1/GIRK2c exhibited baclofen-induced currents of comparable size (Fig. 1A,B), with similar activation and deactivation kinetics (Fig. 1C,D). Furthermore, no difference in the EC50 for baclofen activation of GIRK1/GIRK2a or GIRK1/GIRK2c channels was observed (Fig. 1E–G), indicating that alternative splicing of GIRK2 does not impact the sensitivity of the prototypical neuronal GIRK channel to GABABR activation in a typical mammalian expression system.
