Fig. 2. The effect of succinylcholine (SuCh) on acetylcholine (ACh)–mediated responses in human α1β1δε nicotinic ACh receptor expressed in  Xenopus oocytes voltage clamped at −60 mV. (  A ) ACh, 1 μm, was coapplied with various concentrations of SuCh. Current responses in each oocyte were normalized to the peak current and maximal net charge response to ACh in each oocyte yielding the concentration-response relations shown on the  right . ACh, 5 μm, was coapplied (  B ) or preapplied (  C ) for 55 s with SuCh. The ACh responses in each oocyte were normalized to the ACh precontrols (see Materials and Methods). The preapplication SuCh current was subtracted from the ACh current in preapplication experiments. Representative current traces from a single oocyte are shown on the  left with ACh and SuCh added as indicated by the  horizontal bars . For concentration-response curves, data are presented as mean ± SEM. When no error bars are seen, they are smaller than the symbol.