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 (B_max) of 115 ± 13 fmol/mg protein and affinity (K_D) of 5.2 ± 0.7 nM. Plasma membrane binding demonstrated a B_max of 529 ± 25 fmol/mg protein and K_D 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.