Pharmacological and Biochemical Characterization of Rat Hippocampal 5‐Hydroxytryptamine 1A Receptors Solubilized by 3–[3–(Cholamidopropyl)dimethylammonio]‐1‐Propane Sulfonate (CHAPS)

Rat hippocampal 5‐hydroxytryptamine 1A (5‐HT 1A ) binding sites were solubilized with a yield of 34% using 3–[3–(cholamidopropyl)dimethylammonio]‐1‐propane sulfonate (CHAPS, 10 m M ) as detergent. Kinetic analyses of [ 3 H]8‐hydroxy‐2–(di‐ n ‐propylamino)tetralin ([ 3 H]8‐OH‐DPAT) binding indicated that the 5‐HT 1A sites exhibit the same properties in the soluble form as in the membrane‐bound form. Furthermore, a positive correlation ( r = 0.988) was found between the respective pIC 50 values of a series of agonists and antagonists to inhibit [ 3 H]8‐OH‐DPAT binding to either soluble or membrane‐bound 5‐HT 1A sites. Gel filtration through Sephacryl S‐400 as well as chromatography on wheat germ agglutinin (WGA)‐agarose did not affect the modulation by guanine nucleotides (5′‐guanylylimidodi‐phosphate) of [ 3 H]8‐OH‐DPAT binding which suggests that the 5‐HT 1A binding subunit is a glycoprotein tightly attached to a G protein even in its soluble form. The [ 3 H]8‐OH‐DPAT binding material eluted from Sephacryl S‐400 had an apparent molecular mass of 155 kilodaltons, as expected from a heterodimer with one binding subunit (∼60 kilodaltons) and one G protein (∼80 kilodaltons). Marked enrichment in 5‐HT 1A binding sites relative to other soluble proteins was found in the peak fractions eluted from Sephacryl S‐400 (by sixfold) and WGA‐agarose (by 26‐fold) columns, suggesting that these chromatographic steps might be of interest for the purification of central 5–HT 1A receptors.