Fig. 7.

Upregulation of total α4β2 receptors after chronic nicotine incubation. Specific [³H]nicotine binding to homogenized membranes is upregulated by nicotine. Oocytes were injected with α4 and β2 subunit cRNAs. Twenty-four hours later, oocytes were placed in ND96+Ca in the absence or presence of various concentrations of nicotine for 24 hr. After preparation of homogenized membranes, binding assays were performed using 60 nm [³H]nicotine. The plot shows a dose–response curve constructed from the relative increase in specific [³H]nicotine binding to homogenized membranes at each nicotine incubation concentration. Data are plotted as the amount of specific [³H]nicotine binding for oocytes incubated in nicotine compared with the specific [³H]nicotine binding for control oocytes not incubated in nicotine (n = 16–20 oocytes per data point).