Figure 1. α5 deletion increases the nAChR sensitivity to agonist.

The peak amplitude of the currents (I_peak) evoked by the indicated concentrations of either ACh or cytisine were measured and normalized to the maximal response (I_max) (maximal [ACh], 500 μM; maximal [cytisine], 300 μM). An average of two to seven amplitudes are plotted as a function of the agonist concentration. ▴, data from the control neurones; ⋆, data from α5 minus neurones. A, the dose-response curve for cytisine in control neurones was fitted as a simple sigmoidal curve indicating an EC₅₀ of 61.6 μM and an apparent Hill coefficient of 1.29. In α5 minus neurones the cytisine dose-response curve indicated an EC₅₀ of 17.3 μM and an apparent Hill coefficient of 1.57. B, dose-response curves to ACh. ▴, data from control neurones; ⋆, data from α5 minus neurones. Under control conditions, the concentration dependence of ACh-evoked currents was sigmoidal with an EC₅₀ of 76.6 μM and an apparent Hill coefficient of 1.74. Following the deletion of α5, two components of the ACh dose-response curve were resolved: one with an EC₅₀ of 8.47 μM and the other with an EC₅₀ of 47.48 μM. The apparent Hill coefficient for ACh was 2.63.