Figure 1. Concentration-Effect Curve for ACh Simulated ⁸⁶Rb⁺ Efflux and Katz-Thesleff Models for HS and LS Activity.

The upper panel of this figure shows the ACh concentration effect curve for stimulation of ⁸⁶Rb⁺ efflux. Each data point represents the mean ± SEM for six independent studies. The solid line is the fit of the data to a two component model as described in the methods. The two dashed lines are the individual theoretical curves for the HS and LS components. The cyclical Katz-Thesleff diagrams in the boxes below the main figure illustrate the model used to evaluate the desensitization data. HS and LS ⁸⁶Rb⁺ efflux observed following stimulation at each [ACh] are designated E_HS and E_LS, respectively. The ACh concentrations that elicit 50% maximal HS and LS ⁸⁶Rb⁺ efflux are designated, EC_HS and EC_LS, respectively. The apparent K_D for binding of the ligand (D) to the unliganded desensitized state of the receptor subtypes (R*_HS and R*_LS) are designated K_D-HS and K_D-LS. K_UN-HS and K_UN-LS are the equilibrium constants between the unliganded ground state (R_HS and R_LS) and unliganded desensitized state (R*_HS and R*_LS) and K_des-HS and K_des-LS are the equilibrium constants between the liganded active receptors (R_HS-ACh and R_LS-ACh) and the liganded desensitized receptors.