14(R),15(S)-epoxyeicosatrienoic acid (14(R),15(S)-EET) receptor in guinea pig mononuclear cell membranes

A high affinity binding site for 14(R),15(S)-EET, one of the major cytochrome P-450 metabolites of arachidonic acid (AA) in blood vessels, liver, kidney and urine of patients with pregnancy-induced hyertension, has been identified in a membrane preparation from guinea pig mononuclear (GPM) cells. Using a radioligand assay, binding of 14(R),15(S)-[³H]EET to its receptor site was saturable, specific and reversible. Scatchard analysis of saturation binding studies yielded a dissociation constant (K(d)) of 5.7 X 10^-9 M, and maximum number of binding sites (B(max)) of 2.4 pmol/mg membrane protein. The specificity of the binding site was determined by competition studies. 14(S),15(R)-EET and 8,9-EET had a K(i) of 6.3 and 8.8 nM, respectively, followed by 12(R)-HETE and LTD₄. 12(S)-HETE and 5,6-EET were even less effective as a competitive inhibitor of radioligand binding with K(i) values from 2 to 20 μM. Receptor antagonists for TxA₂, LTB₄, LTD₄ and PAF failed to displace 14(R),15(S)-[³H]EET from its binding site on GPM cell membranes. The results correlate well with the reported biological functions of 14,15-EET. In view of its potent biological activities, 14,15-EET may exert its cellular function through the binding and activation of its stereo-specific cell surface binding sites or receptor.