V1-like [Arg8]vasopressin binding sites occur in rat hepatocyte nuclei

Arginine vasopressin binding site characterization was performed on purified nuclei and plasma membranes from livers of Sprague-Dawley rats. [125I][d(CH2)5,Sarc7,Arg8]vasopressin, a selective V1 vasopressin receptor antagonist radioligand, bound to the nuclei in a protein concentration and time dependent manner. Scatchard analysis of nuclear binding sites revealed a single binding site with maximal binding site density (Bmax) of 115 ± 13 fmol/mg protein and affinity (KD) of 5.2 ± 0.7 nM. Plasma membrane binding demonstrated a Bmax of 529 ± 25 fmol/mg protein and KD of 1.9 ± 0.1 nM. The displacement profile for nuclear binding sites using vasopressin analogues was similar to that for plasma membrane binding sites and was typical of a V1 vasopressin receptor type. There was no evidence of V2-like vasopressin receptor binding using [3H]des-Gly-NH29[d(CH2)5,D-Ile2,Ile4,Arg8]vasopressin, a selective V2 vasopressin receptor radioligand, in the nuclear or membrane fractions. These results suggest the existence of nuclear V1-like vasopressin binding sites.