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 Kd 1 = 3.66 ± 0.92 nM and Kd 2 = 20.4 ± 0.50 nM corresponding respectively to a maximun number of binding sites : Bmax 1 = 0.83 ± 0.23 pmol/mg protein Bmax 2 = 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 maximun amount of binding in midbrain and hippocampus. These data suggest a biochemical and physiological role of PAF in brain.