A, relative potentiation of the +L264 response during a train of ten 150 ms pulses of 100 nm ACh spaced 2, 5, 10, 20 or 40 s apart. Error bars are ±s.e.m.B, changes in the peak WT, +L264 and S252F responses during a train of ten 500 μm ACh pulses (10 ms) spaced 5 s apart. Holding potential, Vh =−50 mV. C and D, potentiation of the +L264 100 nm ACh response was reversible. C, potentiation of the +L264 response during a series of ten 300 ms pulses of 100 nm ACh spaced 5 s apart. Downward deflections of traces show the individual ACh responses. D, potentiation of the +L264 response in the same oocyte 3 min after the first pulse train. Note that the initial ACh response in D has returned to nearly the same level as the initial response in C and that both pulse trains induce the same amount of potentiation.