Figure 2
Positive allosteric modulation by divalent cations requires E44. ACh dose-response curves for the parental C115A/L247T (A) and the E44C mutant (B) in the absence (open squares) and presence (filled squares) of 10 mM BaCl2. Data are fitted to the Hill equation (solid lines). The positive allosteric modulation (leftward shift in the dose response curve) typically exhibited by α7 AChRs (A) is lost in the E44C mutant (B). Data are mean values (± SEM) from three determinations, normalized to the maximal value of the Hill equation fit of each data set. Hill coefficients for C115A/L247T (A): 2.5 ± 0.2 (open squares, -Ba2+), 1.9 ± 0.4 (filled squares, +Ba2+); and for the E44C mutant (B) 1.7 ± 0.2 (open squares, -Ba2+), 2.9 ± 0.7 (filled squares, +Ba2+).