Replacement of the Slo1 S6 segment with the Slo3 sequence abolishes sensitivity to paxilline. (A) Replacing the Slo1 S5–P loop–S6 segment with the homologous Slo3 sequence (chimera MC2) abolishes paxilline sensitivity. The MC2 construct is diagrammed at the top. Traces show MC2 currents activated with 10 µM Ca²⁺ at +200 mV with and without 500 nM paxilline. (B) Paxilline has no effect on MC2 G-V curves (n = 4 patches). (C) Paxilline sensitivity persists after replacement of the Slo1 S5 segment with the homologous Slo3 sequence. The MC28 construct is diagrammed at the top. Traces show MC28 currents activated with 10 µM Ca²⁺ at +180 mV with and without paxilline. (D) G-V curves for MC28 with and without 50 nM paxilline (n = 3 patches) are shown. Red lines correspond to a fit of Eq. 1, with K_bc = K_bo = 30.4 ± 1.7 nM with no voltage dependence. (E) Paxilline sensitivity is lost when the Slo1 S6 segment is replaced with the homologous Slo3 sequence. The MC10 construct is diagrammed at the top. Traces show MC10 currents activated with 0 Ca²⁺ at +200 mV with and without paxilline. MC10 is strongly activated by Ca²⁺, but like Slo3 and MC13, it is also strongly blocked by µM Ca²⁺. (F) G-V curves are shown for MC10 with and without paxilline (n = 4 patches).