Fig. 9.

Inhibition of [³H]NMS binding to wild type and mutant (D103N) M₂ muscarinic receptors by gallamine. The binding of [³H]NMS (1 nM) to homogenates of cells expressing wild-type and mutant (D103N) M₂ muscarinic receptors was measured at 37°C in the presence of increasing concentrations of gallamine. The data represent the mean binding values ± S.E.M. of three experiments, each done in triplicate. The theoretical curve represents the least-squares fit of a four-parameter-logistic equation to the data. The plateau (Y′) and IC₅₀ values were then corrected using eqs. 10 and 11 to estimate the cooperativity of the gallamine-NMS interaction (α) and dissociation constant of gallamine for the free receptor (K).