Fig. 3. Identification of halothane-responsive domain of IK. (A ) Inhibition of IK, SK1, and chimera channels by halothane. Inside-out patches from oocytes expressing IK, SK1, and chimera channels were excised and examined for halothane response. Currents were measured at a membrane potential of −100 mV in the presence of 10 μm Ca²⁺. Both 1 mM and 10 mm halothane were applied to measure the inhibition. The leak currents were estimated by EGTA application and were subtracted to calculate the percentage of inhibition. Data are shown as mean ± SEM. Leak subtracted total currents were 1,073 ± 926 pA (n = 13), 534 ± 232 pA (n = 12), 1,018 ± 604 pA (n = 4), 163 ± 73 pA (n = 4), 2,746 ± 1030 pA (n = 9), 2,233 ± 349 pA (n = 16), and 3,676 ± 657 pA (n = 5) for IK, SK1, chimeras A, B, C, D, and E, respectively. (B ) The amino acid sequence of the halothane-responsive domain of IK. The defined domain of IK is aligned with the corresponding domain of SK1. Identical residues are boxed. The predicted pore and N-terminal half of the S6 domain are indicated by bars .