Fig. 7. The effects of the mutation ζ1-N598Q on the voltage dependence of block by morphine. (  A ) The current–voltage relationships of the ε2/ζ1-N598Q channel before and during perfusion of 300 μM morphine. The measured current responses were normalized to the control current responses at −70 mV before morphine perfusion (n = 6). (  B ) The effects of the membrane potential on the extent of inhibition of the ε2/ζ1 and ε2/ζ1-N598Q channels by 300 μM morphine. The K^d(0)values (mM) for morphine of the ε2/ζ1 and ε2/ζ1-N598Q channels were 3.8 ± 0.5 and 6.5 ± 1.0, respectively, and the zδ values of those were 1.0 ± 0.04 and 0.6 ± 0.06, respectively (n = 6–8).