A highly conserved mutation in S6, E275D, enhances channel opening probability. (A) Currents recorded from an oocyte expressing E275D Slo2.1 channels without NFA treatment. (B) I-V_t relationship for E275D Slo2.1 channels with [K⁺]_e of 2 and 104 mM (1 ng cRNA/oocyte; 2 d expression; n = 8). (C) G-V relationship for E275D channels calculated from I_Slo2.1 recorded from oocytes bathed in K104 solution (n = 4). Data were fitted with a Boltzmann function (smooth curve) to estimate V_0.5 (92.4 ± 1.4 mV), z (0.48 ± 0.01 e), and minimum G/G_max (0.14). (D) Relative amplitudes of instantaneous (A_inst), and the fast (A_fast) and slow (A_slow) time-dependent components of E275D I_Slo2.1. (E) Time constants for activation of E275D I_Slo2.1. For D and E, oocytes were injected with 1 ng cRNA and recorded 2 d later (n = 11). (F) [NFA]–response relationship for E275D Slo2.1 channels. Data were fitted with a logistic equation (smooth curve) to calculate EC₅₀ (192 ± 25 µM) and n_H (1.08 ± 0.09, n = 10). (G and H) E275D I_Slo2.1 recorded in the same oocyte under control conditions (G) and after further activation by 3 mM NFA (H). V_h was −90 mV and pulses were applied in 20-mV steps to a V_t that ranged from +80 to −140 mV. (I) Mean I-V_t relationships for oocytes expressing E275D Slo2.1 channels (1 d after injection with 0.5 ng cRNA) under control conditions and after treatment with 3 mM NFA (n = 5). (J and K) E275D I_Slo2.1 recorded in the same oocyte under control conditions (J) and after further activation by intracellular loading with NaCl (K). V_h was −90 mV and pulses were applied in 20-mV steps to a V_t that ranged from +80 to −140 mV. (L) Mean I-V_t relationships for oocytes expressing E275D Slo2.1 channels (n = 11) under control conditions (1 d after injection with 0.4 ng cRNA) and after NaCl loading (NaCl), and uninjected oocytes (n = 5) before (control) and after NaCl loading (NaCl). Error bars indicate mean ± SEM.