Neurotensin receptors on the rat liver plasma membranes

Abstract

Neurotensin (NT) is now classified as a brain-gut peptide in the central nervous system and gastrointestinal tract. In the present study, we characterized the NT receptors on the rat liver plasma membranes. The specific binding of [ 3H]NT was time dependent, reversible, and saturable. Scatchard analysis of the specific binding data yielded two classes of binding sites, a high affinity site and a low affinity site. The average maximum number of binding sites (B max) amounted to 13.3 ± 1.1 fmol/mg protein at high affinity site and 122.3 ± 21.5 fmol/mg protein at low affinity site, respectively. The dissociation constant (Kd) had values of 0.39 ± 0.01 nM at high affinity site and 8.1 ± 1.1 nM at low affinity site, respectively. The amount of specifically bound [ 3H]NT was significantly reduced in the presence of mono and divalent cations, EDTA, EGTA and a peptidase inhibitor bacitracin. NT 1–13 competed with [ 3H]NT for its binding site with an IC 50 of 0.19 nM at high affinity site (0.2 nM concentration of [ 3H]NT) and 0.7 nM at low affinity site (4.0 nM concentration of [ 3H]NT). Xenopsin, a NT analogue separated from the skin of Xenopus laevis, was equipotent (IC 50 0.75 nM) with NT 1–13 at 4.0 nM concentration of [ 3H]NT. C-terminal sequence of NT contains the structure necessary for interaction with NT binding sites whereas N-terminal sequence had no binding activity. Since NT has a hyperglysemic and a hypercholesterolemic effects in rats, these NT receptors on the rat liver plasma membranes may be involved in the hyperglycemia and/or hypercholesteroremia induced by NT.