Fig. 4.

Cortical D₁ receptors, but not D₅ or D₂ receptors float on sucrose density gradients. Western blot analysis was conducted using discontinuous sucrose gradient fractions, and shown in the figure are representative gradient profiles. A, D₁ receptor-containing membranes localize to fractions where the lipid raft protein flotillin (D) and the caveolar protein caveolin (E) are found. D₁ receptors are also present in diverse detergent-soluble membranes and in the detergent-resistant pellet, where PSD-95 (F) is located. B, D₅ receptors are only detectable in the 200,000g supernatant (cytoplasmic) fraction. C, D₂ receptors are distributed between the cytoplasmic, detergent-resistant pellet and detergent-soluble fractions, but are clearly absent from the raft fraction. All panels were derived from the same gradient. Graph inserts on the right represent densitometric quantification of the immunoreactivity in each fraction (compiled from two independent experiments) as a percentage of summed immunoreactivity in all fractions, for each individual protein.