Calcium potentiation of ACh-elicited macroscopic currents for wild-type and mutant α7 nAChRs. (a) Left: Recordings of current as a function of time in the whole-cell configuration following successive 1.5-s applications of the indicated concentrations of ACh with, without, or with 1.8 mM Ca²⁺, at a membrane potential of −50 mV and bandwidth of 5 kHz (see Materials and methods). Currents elicited by 10 and 100 µM ACh were recorded from different cells. For each cell, currents elicited by the same concentration of ACh were compared in the absence and presence of calcium. Right: Plots of the amplitude of the peak current averaged for four to six cells per condition. (b–d) Results are shown for the indicated mutants as in a. For wild-type α7 activated by 100 µM ACh, the time course of current decay is fitted by the sum of two exponential components: τ_fast = 70 ± 27 ms (relative area 0.47 ± 0.22) and τ_slow = 652 ± 296 ms (relative area 0.34 ± 0.20); n = 27. Error bars represent the SD.