Fig. 7. Tertiapin block of mutant G protein-coupled inwardly rectifying potassium 3.2 (GIRK2) channels. (A) Current traces were recorded from Xenopus oocytes expressing S177T GIRK2 channels and obtained at membrane potentials ranging from +40 to –150 mV in 10-mV increments in 90 mM K⁺ in the absence and presence of tertiapin-Q (TPN_Q), a nonoxidizable derivative of tertiapin, at 0.5 m M. (B) Oocytes expressing S177T, S177W, and N94Y–S177W mutants were exposed sequentially to 90 mM Na⁺ (long dashes) and 90 mM K⁺ in presence (short dashes) or in absence (solid line) of 0.5 m M TPN_Q. Only traces at –150 mV are shown. (C) Normalized remaining current (I/I₀) after exposing S177W and N94Y–S177W channels to various concentrations of TPN_Q. The curves superimposed on the data points correspond to the fits of equation I/I₀ = K_i/(K_i + [TPN_Q]). The K_i values determined from the fits are 6 and 7 nM for S177W and N94Y–S177W GIRK2 channels, respectively.