Pharmacological characterization of the Raji lymphoblast platelet‐activating factor receptor

Abstract

AbstractPrevious studies in our laboratory have described the presence of high‐affinity plateletactivating factor (PAF) binding sites on the B lymphoblast cell line, Raji. In the present study, PAF receptor antagonists were used to examine the specificity of [3H]PAF binding and PAF‐induced intracellular calcium mobilization in this human lymphocyte cell line. In binding studies conducted at 4°C, PAF receptor antagonists competed with [3H]PAF for binding to Raji lymphocytes with the following rank order of potency: Ro 19‐3704 ∼ CV‐6209 > CV‐3988 > BN52021 > alprazolam. This order of potency is similar to those described for binding studies in platelets and neutrophils. The PAF receptor antagonists CV‐6209 and alprazolam inhibited the PAF‐induced calcium changes and PAF binding with similar potencies, indicating that the high‐affinity PAF binding sites are functional receptors coupled to calcium mobilization. The calcium channel antagonists verapamil, diltizem, and nimodipine inhibited Raji lymphoblast PAF binding with similar potencies, but had no effect on PAF‐induced intracellular calcium changes, suggesting the possibility that these compounds are not true competitive antagonists. These studies provide evidence that the Raji lymphoblast PAF receptor is pharmacologically similar to PAF receptors found on platelets and neutrophils, and thus could be of use as a model system to study the PAF receptor.