Increase in QC is triggered by block of nAChRs containing α1 subunits. A, QC was measured before and in the presence of D-TC (0.1 μm) in control muscle (n = 8 mice, 22 NMJs), in muscle pretreated with atropine (10 μm) to block muscarinic AChRs (2 mice, 5 NMJs), in muscle pretreated with α-CtxArIB (17 nm) to block α7 containing nAChRs (3 mice, 9 NMJs), and in muscle from mice lacking nAChRs composed of α7 subunits (6 mice, 20 NMJs). There was no significant difference in baseline QC among the 4 groups (F(3,15) = 0.805, p = 0.499, ANOVA) and D-TC triggered a significant increase in QC in all 4 groups (Table 1). B, QC is significantly increased by α-Ctx MI (40 nm), which blocks nAChRs containing the α1 subunit. Control, n = 3 mice, 30 NMJs; in the presence of α-Ctx MI, n = 3 mice, 50 NMJs. ANOVA, F(2,6) = 9.787, p = 0.0001.