Figure 1.

Paxilline blocks Slo1, but not Slo3 current. (A) Traces show block of Slo1 by paxilline, and the general topology of the Slo1 α subunit is shown on the top. Currents were activated by a step to +120 mV in an inside-out patch exposed to 10 µM Ca²⁺ with the indicated concentrations of paxilline. The holding potential was 0 mV, but the command steps were preceded by a brief 10-ms step to −140 mV. (B) The time course of paxilline block and unblock of Slo1 current is illustrated. Steps were to +100 mV. (C) G-V curves were generated from steady-state current levels for recordings in the absence and presence of paxilline (n = 4–7 patches). For this set of data, paxilline was applied at increasing concentrations, and full washout was not usually achieved (see B). Red lines correspond to a fit of Eq. 1, with K_b = 10.6 ± 0.49 nM with z_c = z_o = 0 e. (D) 500 nM paxilline is without effect on MC13 currents activated at +200 mV with pH 8.5. The composition of the MC13 construct is schematized at the top with Slo3 sequence shown in red. (E) MC13 currents are unaltered by 500 nM paxilline during 6 min of application. (F) 500 nM paxilline has little effect on MC13 G-V curves.