Prostaglandin-E1-binding sites in rabbit erythrocyte membranes

Prostaglandin E1 (PGE1) binding sites have been identified on rabbit erythrocyte membranes. The binding of PGE1 to the membranes was found to be highly specific, reversible, and saturable. The high-affinity binding sites had a dissociation constant (Kd.1) of 5.6 +/- 1.2 nM with a binding capacity of 210 +/- 51 fmol/mg protein, whereas the low-affinity binding sites had a dissociation constant (Kd.2) of 22 +/- 6.4 microM, and a binding capacity of 321 +/- 78 pmol/mg protein. Incubation with PGE1 did not activate adenylate cyclase in the membranes. Preincubation of rabbit erythrocyte membranes with physiological amounts of insulin (1.5 nM) resulted in an increase of PGE1 binding to the membranes from 241 +/- 65 to 429 +/- 85 fmol/mg protein. The insulin-induced increase in PGE1 binding was due to an increase in binding sites (both high-affinity and low-affinity binding sites) rather than to an increase in the affinity of the binding sites. Treatment of erythrocyte membranes with PGE1 at concentrations (4.0-7.5 nM) which were within the Kd.1 value of the high-affinity binding sites, resulted in a significant reduction in membrane fluorescence anisotropy (0.27 +/- 0.005-0.21 +/- 0.003). Use of higher concentrations (> 15 nM) of PGE1 reversed the effect of its lower concentration on the membrane anisotropy.