Prostaglandin E2 Receptors in the Chicken Spinal Cord:

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Abstract
Prostaglandins (PGs) are neuroactive substances which act in the vicinity of their site of synthesis through receptors coupled to G-proteins. Since large amounts of PGE2 can be synthesized by chicken spinal cord, binding sites for PGE2 were looked for in various cell fractions of spinal cord. In the 17,000 g pellet incubated with 0.3 nM [3H]PGE2, 70% of ligand was specifcially bound. Two types of PGE2 binding site were characterized high affinity, low capacity binding sites (KD1 1.34 nM, Bmax1 34.5 fmol/mg prot) low affinity, high activity binding sites (KD2 2.23 .mu.M, Bmax2 13.2 pmol/mg prot). The high affinity binding sites fulfil several requirements for being receptors to PGE2: since the KD1 is increased in the presence of the GTP analogue, Gpp(NH)p, these binding sites would be regulated by a G-protein; a desensitization was obtained by an excess of unlabelled PGE2 and reversed by Gpp(NH)p; the competition experiments between PGE2 and various prostanoids pointed to PGE2 receptors such as EP2 or EP3. The receptor characteristics of the low-affinity binding sites were not investigated. Hence, our results support the presence of two of PGE2 binding site in the chicken spinal cord; a high affinity site, which corresponds to a PGE2 receptor responding to nanomolar concentrations and a low affinity site sensitive to micromolar concentrations of PGE2.