Specific binding of prostaglandin D2 to rat brain synaptic membrane. Occurrence, properties, and distribution

Prostaglandin (PG) D2 bound specifically to a particulate fraction rich in the synaptic membrane of rat brain. The binding was dependent on time and temperature, equilibrium being reached after 5 min at 37 degrees C. The specific binding constituted about 70% of the total binding at 37 degrees C, and 55% at 0 degrees C. The maximal binding was obtained in the presence of 100 mM sodium ion and at pH 8. The equilibrium dissociation constant and the maximal concentration of binding sites as determined by Scatchard analysis were 28 +/- 7 nM and 0.45 pmol/mg of protein (n = 3), respectively. Hill coefficient was 1.15, indicating a single entity of binding sites and no cooperativity. The binding sites were highly specific for PGD2; the Ki values for PGD1 and PGF2 alpha were 523 and 693 nM, respectively. Other PGs including 13,14-dihydro-15-keto-PGD2, an inactive metabolite of PGD2, had 150- to 1000-fold lower affinities than PGD2. The binding was inhibited by boiling or treatment with proteases, phospholipases, or beta-galactosidase. The specific activity of PGD2 binding was highest in the pituitary gland, followed by the hypothalamus and the olfactory bulb od the rat brain, this pattern being almost parallel to that of the cytosolic NADP-linked PGD2 dehydrogenase activity. The results suggest that PGD2 plays a significant role in these regions of the rat brain.