GrTX-SIA interacts with two K V 2.1/Na V 1.6 VSD chimeras. (A) Example potassium ion currents (top row) elicited by depolarizations to the maximum voltage of the voltage-activation curve (second row) for the four KV2.1/NaV1.6 VSD chimeras (VSDI–VSDIV) in the absence (black) and presence of 1 µM GrTX-SIA after a 4-min incubation period. The holding voltage was −90 mV and the tail voltage was −60 mV (−80 mV for DIII). The second row of panel A shows the normalized current–voltage relationships for the corresponding KV2.1/NaV1.6 VSD chimeras before and after the addition of 1 µM GrTX-SIA, normalized to the maximal control current. *P < 0.05 compared with recordings before toxin addition. (B) Representative example of partial KV2.1/NaV1.6 VSDII inhibition (left) by 1 µM GrTX-SIA followed by wash-off with ND-100 (Y-axis: percentage of current remaining assessed with 5 s pulses to +50 mV). Current amplitude completely recovered during a 4-min wash-off period (black circles). Right panel shows virtually complete KV2.1/NaV1.6 VSDIV inhibition by 1 µM GrTX-SIA followed by incomplete wash-off with ND-100 after 10 min. Data shown are mean ± SEM of n = 7 oocytes for KV2.1/NaV1.6 VSDI, and n = 5 oocytes for KV2.1/NaV1.6 VSDII–VSDIV.