Figure 1.

Binding of N-α-[methyl-³H]histamine ([³H]-NMHA) to membranes from CHO-K1-hH₃R_WT or CHO-K1-hH₃R_A280V cells. (A) Saturation binding. Cell membranes were incubated with the indicated concentrations of [³H]-NMHA and specific receptor binding was determined by subtracting the binding in the presence of 10 μM histamine from total binding. Points are means ± SEM from triplicate determinations from a single experiment, which was repeated a further three times. The line drawn is the best fit to a hyperbola. Best-fit values for the equilibrium dissociation constant (K_d) and maximum binding (B_max) are given in the text. (B,C) Inhibition by H₃ receptor ligands. Membranes from CHO-K1-hH₃R_WT (B) or CHO-K1-hH₃R_A280V cells (C) were incubated with 1.5 nM [³H]-NMHA and the indicated drug concentrations. Values are expressed as percentage of control specific binding and are averages ± ranges of duplicates from a single experiment, repeated a further two to four times with similar results. The line drawn is the best fit to a logistic equation for a one-site model. pK_i values calculated from the best-fit IC₅₀ estimates are compared in Table 1.