Fig. 6. S177W G protein-coupled inwardly rectifying potassium 3.2 (GIRK2) channel allows K⁺ and Na⁺ but not N-methyl-D-glucamine (NMDG) to permeate the channel, whereas wild-type and S177T GIRK2 allow only K⁺ permeation. Shown are representative current traces (Left) and averaged current–voltage relations (Right) obtained from Xenopus oocytes bathed in an external solution containing 90 mM K⁺, 90 mM Na⁺, or 90 mM NMDG. Currents were recorded at membrane potentials ranging from +40 to –150 mV in 10-mV increments. Only traces at –150 mV are shown in K⁺ (solid line), Na⁺ (long-dash line), and NMDG (short-dash line). Points in the I–V curves represent mean ± SEM in 90 mM Na⁺ (filled circles), 90 mM K⁺ (open triangles), and 90 mM NMDG (filled squares).