The hepatic angiotensin II receptor. II. Effect of guanine nucleotides and interaction with cyclic AMP production.

Abstract

Guanine nucleotides were observed to modify the binding of '261-angiotensin I1 t o rat hepatic plasma membrane receptors.G T P and its nonhydrolyzable analogues greatly increased the dissociation rate of bound "'I-angiotensin I1 and altered hormone binding t o the receptor under equilibrium conditions.In the absence of GTP, '261-angiotensin 11 labeled both high affinity sites (&I = 0.46 m, Nl = 650 fmol/mg) and low affinity sites (&z = 4.1 m, Nz = 1740 fmol/mg).In the presence of guanine nucleotides, the affinities of the two sites were unchanged, but the number of high affinity sites decreased markedly to 52 fmol/mg.In analogous experiments using the angiotensin I1 antagonist, "'1-sarcosine',Ala'-angiotensin I1 ("'I-saralasin), guanine nucleotides minimally affected the interaction of "'I-saralasin with its receptor, increasing the dissociation rate 1.9-fold and the Kd 1.4-fold.The guanine nucleotide inhibition of agonist binding required a cation such as Na' or M8', with a maximal effect occurring at about 1 m~ M&'.In liver plasma membranes prepared in EDTA, angiotensin I1 inhibited basal and glucagon-stimulated adenylate cyclase activities by 30% and lo%, respectively.Angiotensin I1 also caused a 40% inhibition of glucagon-stimulated cyclic AMP accumulation in intact hepatocytes, with a half-maximal effect occurring at 1