Coverslips containing transfected HEK cells or infected hippocampal neurons were transferred to a chamber containing a low-K+ bath solution (in mM): 130 NaCl, 5.4 KCl, 1 CaCl2, 1 MgCl2, 5.5 D-glucose, 5 HEPES/NaOH (pH 7.4). Neurons were visualized using an Olympus IX-70 microscope. Fire-polished borosilicate patch pipettes (3–5 MΩ) were filled with K-gluconate pipette solution (in mM): 140 K-gluconate, 2 MgCl2, 1.1 EGTA, 5 HEPES, 2 Na2-ATP, 0.3 Na-GTP, and 5 phosphocreatine (pH 7.2). Upon achieving whole-cell access, cells were held in voltage-clamp mode at −70 mV (with no correction for liquid junction potential). GIRK currents were measured in a high-K+ bath solution containing (in mM): 120 NaCl, 25 KCl, 1 CaCl2, 1 MgCl2, 5.5 D-glucose, 5 HEPES/NaOH (pH 7.4); GPCR agonists were dissolved in the high-K+ bath solution, which was then applied directly to the cell using a ValveLink 8.2 rapid perfusion system (AutoMate Scientific, Inc.; Berkeley, CA). Whole-cell currents were measured at room temperature with hardware (Axopatch-200B amplifier, Digidata 1322A) and software (pCLAMP v. 8.2) from Molecular Devices, LLC (Sunnyvale, CA). All currents were low-pass filtered at 2
