Specific receptor sites for PAF in iris and ciliary body of the rabbit eye

The existence cf specific binding sites by using tritiated 1-0-alkyl-2-0-acetyl-sn-glycero-3-phos-phocholine (3H-PAF) was investigated on iris and ciliary body tissue of pigmented rabbit eyes. The binding was saturable, specific, time-dependent and reversible.Scatchard's analysis indicated the presence of two types of binding sites with a Kd1 90 ± 0.47 nM, a Kd2 11.60 ± 0.33 nM, a Bmax1 3.17 ± 0.50 pmol/mg protein and a Bmax2.12 ± 45 ± 2.30 pmol/mg protein for iris tissue, and a Kd4 5.71 ± 0.09 nM, a Kd2 24.40 ± 0.91 nM, a Bmax1 3.41 ± 1.00 pmol/mg protein and a Bmax2 16.60 ± 0.51 pmol/mg protein for ciliary body. The binding was fully displaced by unlabelled PAF in both iris and ciliary body preparations, and partially inhibited by the PAF antagonist BN 52021 in iris tissue.