A specific, photolabile and irreversible antagonist (L662,025) of the PAF-receptor

Abstract

PAF (0.2 μM) induced maximal platelet aggregation in human PRP and [ 3H]-PAF (1 – 5 nM) binding to platelet membrane preparations had Kd value of 3.8 nM and B max of 200 fmoles/mg of protein. Without UV irradiation, a synthetic azido tetrahydrofuran derivative L662,025 was a reversible and competitive PAF-receptor antagonist with IC 50 values of 5.6 ± 0.3 μM (platelet aggregation) and 1.0 ± 0.25 μM (receptor binding). Photolysis of L662,025 in the presence of PRP produced an irreversible inhibition of platelet aggregation and specific binding of [ 3H]-PAF (1 nM). L662,025 did not affect collagen- or ADP-induced human platelet aggregation before or after photolysis. It is a new probe that can be used to identify and characterize the PAF-receptor.