Figure 4.

Kinetics and blockade by α-toxins of I_ACh, in Xenopus oocytes injected with cRNAs for α₇ or α₃β₄ nAChR. Oocytes maintained at a holding potential of −60 mV, were stimulated with pulses of ACh (100 μM) as shown by the top horizontal bars. (A) Two original I_ACh traces (normalized currents) obtained by stimulation with ACh (20 s) in one oocyte expressing α₇ receptors and in another expressing α₃β₄ receptors. (B) Effect of α-conotoxin ImI on I_ACh generated by 1 s pulses of ACh (100 μM) applied to oocytes expressing α₇ receptors. (C and D) Concentration-response curves of α-toxins to block I_ACh in oocytes expressing α₇ nAChR (C) or α₃β₄ receptors (D). Protocols to estimate the blockade exerted by each toxin on I_ACh were as those described in B. Repeated pulses of ACh (1s, 100 μM) generated inward currents that were normalized to 100% (before adding each toxin concentration). The blockade exerted by each toxin concentration was expressed as percentage of the initial current. Data are means ± SE of 5–10 oocytes for each blocker.