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. 2018 Feb 14;38(7):1725–1736. doi: 10.1523/JNEUROSCI.1789-17.2018

Figure 4.

Figure 4.

Upregulation of QC occurs only in blockers with no agonist activity. A, Application of vecuronium triggers upregulation of QC. Left, Plot of average EPC and mEPC amplitude and QC before and after infusion of vecuronium (0.25 μm) at the time indicated. Right, Averaged EPC and mEPC traces before (gray) and in the presence of vecuronium (red) taken from times corresponding to colored symbols on the plot on the left. Below are plots of mean EPC, mEPC, QC, and mEPC amplitude before (n = 10 muscle, 35 NMJs), during (n = 10 muscles, 99 NMJs) and after washout of vecuronium (n = 10 muscles, 45 NMJs. For these experiments, muscle was held at −70 mV and contraction was prevented by addition of 2 μm μ-Ctx (Table 1). B, Application of mecamylamine triggers upregulation of QC. The same experimental protocol was used as described in A for vecuronium. Mecamylamine (12 μm) triggered similar changes in EPC and mEPC amplitude and a similar increase in QC. Bottom summarizes data from 6 muscles before mecamylamine (n = 31 NMJs) and during (n = 32 NMJs) and after washout (n = 43 NMJs) (Table 1). C, Application of succinylcholine fails to trigger upregulation of QC. Left, Plot of average EPC and mEPC amplitude and QC before and after infusion of succinylcholine (1 μm) at the time indicated. D, Averaged EPC and mEPC traces before (gray) and in the presence of succinylcholine (red), taken from times corresponding to colored symbols on the plot shown in C. Bottom, mean data from 10 muscles treated with succinylcholine (500 nm): n = 61 NMJs before, n = 87 NMJs during succinylcholine infusion, and 76 NMJs after washout (Table 1). E, Comparison of changes in mEPC amplitude (gray triangle) and QC (red circle) induced by infusion of ACh (left) or by infusion of mecamylamine (right). All the values shown were normalized to the average value (as 100%) from the beginning of the plots, respectively. Although mEPC amplitude was reduced by a similar proportion, QC increased during mecamylamine infusion, but not ACh infusion. F, Summary of changes in mEPC amplitude and QC induced by BTX (control, 51 NMJs and BTX, 78 NMJs), D-TC (29 and 25), gallamine (33 and 55), mecamylamine (Meca, 31 and 43), vecuronium (33 and 99), succinylcholine (suc, 61 and 87), and ACh (43 and 102). **p < .01. Averaged values were scaled to controls, which were set at 100%.