Figure 2.

Simulations. Effect of the competitor dissociation rate on the recovery of radioligand binding after a fixed-time incubation. Competitor and radioligand parameters, radioligand concentration and incubation time are given in Table 1. For the simulations, the receptor-containing preparation is pre-incubated with different concentrations (abscissa) of competitors with the indicated dissociation t_1/2 till equilibrium is reached. Free competitor molecules are removed and the preparation is further incubated with a fixed concentration (2 nM = 2.K_D) of radioligand for 30 min. Radioligand binding is expressed in percent of control, i.e. binding to receptors pretreated with medium only (i.e. [LR]_c=0). Competitor dissociation t_1/2 values (=0.69/k₄), calculated according to Equation 5 with [LR]_cmax (radioligand binding to receptors pretreated with the highest concentration of each competitor) and the radioligand k₁ and k₂ values (Table 1) are close to the input values: i.e. 6.9, 13.7, 34.4 and 137.6 min respectively. Insert: [LR]_cmax as a function of the dissociation t_1/2 (abscissa, natural logarithmic scale) of distinct competitors (symbols are in red for the competitors displayed in the main panel).