Regulation of (3H) Arginine8Vasopressin Binding to the Rat Renal Medulla by Guanine Nucleotides

Abstract

In rat renal medullary membranes, we have examined modulatory effects of guanine nucleotides on binding of arginine vasopressin (AVP) to its receptor. Equilibrium binding studies analyzed by an iterative curve fitting program revealed an interaction of (³H) AVP with a single class of binding sites with a dissociation constant of 1.4±0.2 nM and a binding site concentration of 201±37 fmol/mg protein (n=6). With the addition of 100 _μM guanylyl-imidodiphosphate (Gpp(NH)p), the binding site concentration was significantly (p < 0.01) reduced to 151±36 fmol/mg protein with no change in receptor affinity. The nonhydrolyzable analogues, guanosine-5₃′-O-(3-thiophosphate) and Gpp(NH)p were the most potent inhibitors of (³H) AVP binding. Guanosine 5′-triphoshate and guanosine-5′-diphosphate were both relatively poor inhibitors. Guanosine-5′-monophosphate and adenosine 5′-triphosphate did not inhibit (³H) AVP binding at concentrations up to 100 μM. Furthermore, 100 μM Gpp(NH)p accelerated the dissociation of (³H) AVP from the receptor. We conclude that guanine nucleotides are important modulators of AVP binding to the V₂ receptor subtype in the renal medulla.