Calcium potentiation depends on the ACh concentration. (a) Left: Plot of the durations of individual channel openings in the presence of 1 µM ACh as a function of time of occurrence during the recording, without or with 1.8 mM Ca²⁺. Recordings were obtained in the cell-attached patch configuration with an applied potential of −100 mV and Gaussian filter of 25 kHz. Left-middle: Comparison of the average channel opening frequency without or with 1.8 mM Ca²⁺, obtained from four to six patches for each condition; channel opening frequency is expressed relative to that in the presence of 1.8 mM Ca²⁺. Right-middle: Comparison of histograms of open dwell times fitted by the sum of either one or two exponentials, without or with 1.8 mM Ca²⁺, respectively. Right: Comparison of the average duration of channel openings without divalent cations or with 1.8 mM Ca²⁺. (b and c) Results are shown as in a, but with ACh concentrations of 10 (b) and 100 (c) μM. Error bars represent the SEM.