Presence of specific binding sites for platelet-activating factor (PAF) in brain.

The existence of specific binding sites for [3H]-labelled PAF ([3H]PAF) was investigated on membrane preparations of gerbil brain. Binding assays of [3H]PAF showed a specific, saturable, reversible and time dependent binding. Scatchard analysis indicated the presence of two apparent populations of binding sites with Kd1 = 3.66 +/- 0.92 nM and Kd2 = 20.4 +/- 0.50 nM corresponding respectively to a maximum number of binding sites: Bmax1 = 0.83 +/- 0.23 pmol/mg protein Bmax2 = 1.1 +/- 0.32 pmol/mg protein. The binding of [3H]PAF was fully displaced by unlabelled PAF and partially inhibited by the PAF antagonist BN 52021 suggesting that BN 52021 interacts only with one site. Distribution of [3H]PAF specific binding revealed a maximum amount of binding in midbrain and hippocampus. These data suggest a biochemical and physiological role of PAF in brain.