Quantal size recorded in WT and TG muscles under conditions of low probability of release (0.2 mm Ca2+, 2.3 mm Mg2+). Evoked and spontaneous responses were combined (see Methods). A sample of PSPs from several cells was taken in the presence of physostigmine (10 μm). A, PSP amplitude. B, PSP rise time (from onset to peak). C, PSPs half-decay time (from peak to half-decay). Numbers of cells analysed are indicated above the bars, number of animals in brackets (similar numbers for A and B). Data were analysed with an unpaired two-tailed t test: *P < 0.05, compared with WT results; ≈P < 0.05, compared with no drug conditions within the same group.