Ligand depletion affecting homologous competition data shifts IC
rightward and distorts the sigmoidal shape of the competition curve. A. Homologous competition of 0.013 nM [3H]EB and α4β2 nAChR at various concentrations of R1T. B. Homologous competition of 13 nM [3H]EB and α4β2 nAChR. Compared with A, the larger [3H]EB concentration leads to an initially larger IC50 at small R1T (Eq. (13)) and a larger R1T concentration needed for the onset of significant ligand depletion. The curves for the five smallest R1T values overlap and form the leftmost solid curve. The competition curves of both A and B are distorted away from sigmoidal shape as ligand depletion increases.