Paxilline does not hinder MTSET modification of A313C. (A; top) The traces show currents activated with 300 µM Ca²⁺ at voltage steps up to 200 mV for channels arising from Slo1-C430S-A313C. (Bottom) Currents were similarly elicited, but after 120 s of application of 1 mM MTSET while holding the patch at −80 mV with 0 Ca²⁺. (B; top) The traces show current for Slo1-C405A-A313C activated with 300 µM Ca²⁺. The patch was then first perfused with 500 nM paxilline for 100 s while holding at −80 mV with 0 Ca²⁺, and then exposed to 1 mM MTSET with 500 nM paxilline for 120 s while still at −80 mV with 0 Ca²⁺. (C) G-V curves summarize results from patches examined for conditions shown in A and B. Because MTSET modification was tested both without and with paxilline, two separate sets of control G-V curves at 300 µM Ca²⁺ are shown. (D) BK currents were recorded in 300 µM Ca²⁺ before (left) and after (top right) modification by 1 mM MTSET, applied for 120 s in 0 Ca²⁺ at −80 mV. Modification is similar to that in A. The patch was then held at 0 mV, 0 Ca²⁺, and then channels were opened by 20 100-msec steps to 160 mV, after which the traces on the bottom right were obtained in 300 µM Ca²⁺. (E) G-V curves correspond to conditions as in D for control, after closed-state modification by 1 mM MTSET, and then after subsequent open-state modification by the same MTSET solution.