The recently discovered endogenous μ receptor selective endomorphin 2 was prepared in tritiated form by a catalytic dehalogenation method resulting in a specific radioactivity of 1.98 TBq/mmol (53.4 Ci/mmol), and used for in vitro labelling of rat brain membranes. The binding was saturable, stereospecific and of high affinity (K(d): 0.97 and 1.12 nM based on kinetic and equilibrium binding studies, respectively). The maximal number of binding sites (B(max)) was found to be 114.8 fmol/mg protein. [3H]Endomorphin 2 was displaced by μ-receptor selective specific peptides and heterocyclic compounds with high affinity, whereas κ and δ receptor specific ligands were much less potent. The K(i) values of endomorphin 1 and 2 in inhibiting [3H]naloxone binding increased by 15-fold in the presence of 100 mM NaCl which indicates the agonist property of these peptides. Endomorphins stimulated [35S]GTPγS binding and inhibited adenylyl cyclase activity which also provides evidence for the agonist character of endomorphins.
|Number of pages||6|
|Journal||Biochemical and biophysical research communications|
|Publication status||Published - Sep 29 1998|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology