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. 2019 Mar 4;151(3):292–315. doi: 10.1085/jgp.201812213

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© 2019 Tilley et al.

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Figure 1. — GxTx modulation of Kv2.1 conductance in whole-cell recordings. (A) Kv2.1 current response to 10-mV increment voltage steps ranging from −80 to +120 mV. The holding potential was −100 mV. Traces were recorded in vehicle (left) or the indicated concentration of GxTx. Voltage stimuli colored identically in all panels. (B) Conductance calculated from the mean current of the last 20 ms of each voltage step. GxTx concentrations are the same as in A. Symbols denote individual cells (n = 4–5). (C) Mean conductance from cells in B. Black circles, control; pink triangles, 10 nM GxTx; red inverted triangles, 100 nM GxTx; dark red diamonds, 1 µM GxTx. Dotted lines, fit of Eq. 1 with x = 1 (vehicle: V_1/2 = 19.4 ± 0.4 mV, z = 1.50 ± 0.02 e₀, A =1.008 ± 0.002; 1 µM GxTx: V_1/2 = 73 ± 2 mV, z = 2.6 ± 0.2 e₀, A = 0.66 ± 0.02); dashed lines, fit of Eq. 1 with x = 4 (vehicle: V_1/2 = −23.6 ± 0.6 mV, z =1.02 ± 0.02 e₀, A = 1.041 ± 0.003; 100 nM GxTx: V_1/2 = 44.5 ± 1.5 mV, z = 1.06 ± 0.06 e₀, A = 0.79 ± 0.04; 1 µM GxTx: V_1/2 = 43 ± 2 mV, z = 1.3 ± 0.1 e₀, A = 0.73 ± 0.04); black lines, fit of Eq. 2 (vehicle: V_independent = −26 ± 6 mV, z_independent = 2.6 ± 0.2 e₀, V_concerted = 12 ± 2 mV, z_concerted = 0.54 ± 0.04 e₀, A = 1.19 ± 0.02; 1 µM GxTx: V_independent = 27 ± 14 mV, z_independent = 2.0 ± 1.4 e₀, V_concerted = 74 ± 13 mV, z_concerted = 1.1 ± 0.1 e₀, A = 0.79 ± 0.18); pink line, fit of sum of fits of Eq. 2 to vehicle and 1 µM GxTx (10 nM GxTx: A_vehicle = 24 ± 2%). (D) Gating schemes underlying fitting from C. C = closed channel, O = open channel, R = resting voltage sensor, A = active voltage sensor. (E) Calculated conductance of channels with varying GxTx stoichiometry. Each voltage sensor has a V_1/2 = 43 mV and z = 1.3 e₀ as in the fit of Eq. 1 to 1 µM in C. (F) Calculated conductance of channels in varying concentrations of GxTx. GxTx stoichiometry from binomial distribution with K_d = 12.7 nM. Channels with zero voltage sensors bound are represented by fit of Eq. 2 to vehicle from C. Channels with GxTx as in E.