Prostaglandin E2 Receptors in the Chicken Spinal Cord: 1. Biochemical Characterization.
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 specifically bound. Two types of PGE2 binding site were characterized (i) high affinity, low capacity binding sites (KD1 1.34 nM, Bmax1 34.5 fmol/mg prot); (ii) low affinity, high capacity binding sites (KD2 2.23 microM, Bmax2 13.2 pmol/mg prot). The high affinity binding sites fulfil several requirements for being receptors to PGE2: (i) 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; (ii) a desensitization was obtained by an excess of unlabelled PGE2 and reversed by Gpp(NH)p; (iii) 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 types 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.
Pralong
E.
E
Institut d'Histologie et d'Embryologie, Faculté de Médecine, Université de Lausanne, rue du Bugnon 9, 1005 Lausanne, Switzerland.
Vesin
M.-F.
MF
Droz
B.
B