Figure 7. The effect of Ch-T on channel open probability depends on [Ca²⁺].

A, representative wild-type hSlo1 (top) and Triple Met mutant (bottom) currents before (thin sweep) and after (thick sweep) Ch-T treatment. The zero, 200 nm, 5 μm, and 120 μm[Ca²⁺]_i currents were elicited in response to pulses from 0 to 120 mV, 0 to 100 mV, −80 to 20 mV, and −130 to −20 mV, respectively. Grey sweeps denote currents in 5 μm[Ca²⁺]_i post-DTT treatment. Dotted lines represent the zero current level. B, representative wild-type hSlo1 G–V curves before (○) and after (•) modification by Ch-T. Currents were first elicited by pulsing to different test potentials in the virtual absence of Ca²⁺. This recording protocol was repeated after bath application of 200 nm, 5 μm, or 120 μm Ca²⁺. Tail currents in zero, 200 nm, 5 μm, and 120 μm[Ca²⁺]_i were measured at −50, −50, −80, and −120 mV, respectively. Following a return to zero Ca²⁺ for treatment with 2 mm Ch-T, the recording protocols were again repeated in zero and then the appropriate [Ca²⁺]_i. The zero, 200 nm, 5 μm and 120 μm[Ca²⁺]_i mean V_0.5 values for the results obtained before and after Ch-T application were 150.8 ± 2.8 and 119.6 ± 4.4 mV (ΔV_0.5=−31.2 mV), 135.5 ± 3.8 and 111.7 ± 2.9 mV (ΔV_0.5=−23.8 mV), 21.8 ± 3.9 and 35.3 ± 2.6 mV (ΔV_0.5= 13.5 mV), and −36.9 ± 15 and −2.6 ± 11 mV (ΔV_0.5= 24.3 mV), respectively. The 5 μm[Ca²⁺]_i mean V_0.5 value obtained after DTT (dotted squares) application was 32.3 ± 2.8 mV (ΔV_0.5= 10.5 mV). C, representative Triple Met mutant G–V curves before (○) and after (•) treatment with Ch-T. The recording protocol was identical to that in B. The 0, 200 nm, 5 μm and 120 μm[Ca²⁺]_i mean V_0.5 values for the results obtained before and after Ch-T application were 155.2 ± 4.7 and 151.7 ± 4.5 mV (ΔV_0.5=−3.5 mV), 150.3 ± 8.4 and 148.2 ± 7.8 mV (ΔV_0.5=−2.1 mV), 31.0 ± 5.9 and 56.7 ± 7.1 mV (ΔV_0.5= 25.7 mV), and −15.6 ± 4.0 and 1.6 ± 1.1 mV (ΔV_0.5= 17.2 mV), respectively. The 5 μm[Ca²⁺]_i mean V_0.5 value obtained after DTT (dotted squares) application was 40.4 ± 7.9 mV (ΔV_0.5= 9.4 mV). The 200 μm[Ca²⁺]_i control mean V_0.5 value (open sideways triangles) was −17.1 ± 2.1 mV. D, wild-type hSlo1 (left) and Triple Met (right) V_0.5 values before (○) and after (•) treatment with Ch-T at different concentrations of [Ca²⁺]_i. The symbols for Triple Met in the control condition may be located directly under those of the Ch-T condition. The error bars in some cases are smaller than the symbol size (n = 3).