Incubation of oocytes with Na_i-loading solution activates I_Slo2.1. (A) Currents recorded from an uninjected oocyte before (control) and after 10-min incubation in Na_i-loading solution. V_t was varied from −140 to +80 mV and applied in 20-mV increments from a holding potential of −80 mV. (B) Currents recorded from an oocyte injected with 3.2 ng Slo2.1 cRNA before (control) and after incubation in Na_i-loading solution for 10 min. V_t was varied from −140 to +80 mV and applied in 20-mV increments from a holding potential of −80 mV. (C) Average I_Slo2.1–V relationship determined after incubation of oocytes in Na_i-loading solution for 10–15 min (n = 8). (D) Kinetics of I_Slo2.1 activated by incubation of oocytes with Na_i-loading solution for 15 min. Left plot summarizes the fast and slow time constants for activation (τfast and τslow) of the time-dependent component of current (n = 15). On the right is a plot of the amplitude of the instantaneous current (I_inst) divided by the total outward current (I_total) (n = 15). (E) Currents recorded from oocytes injected with 3.2 ng Slo2.1 cRNA and incubated in Barth’s solution (top) or Barth’s solution plus 10 µM ouabain for 2 d (bottom). V_t was varied from −160 to +80 mV, applied in 40-mV increments. (F) I-V relationships for uninjected oocytes incubated in Barth’s solution plus 10 µM ouabain for 2 d (open triangle; n = 9) and in oocytes injected with 3.2 ng Slo2.1 cRNA and incubated in Barth’s solution alone (open circle; n = 7) or in Barth’s solution plus 10 µM ouabain for 2 d (filled square; n = 13).