Characterization of the rabbit ventricular myocardial receptor for angiotensin II. Evidence for two sites of different affinities and specificities

GB Wright, RW Alexander, LS Ekstein and MA Gimbrone

Angiotensin II binding sites in a rabbit ventricular myocardial particulate fraction were identified and characterized with the radioligand 125I-angiotensin II. The order of potency in competing with 125I-angiotensin II for these sites was similar to that observed in physiological studies. Computer-assisted analysis of the competition of binding sites for 0.3 nM 125I-angiotensin II by unlabeled angiotensin II (3 X 10(-11) M to 1 X 10(-5) M) demonstrated that optimal fitting of the competition curves was attained with a two-site model having one site of high affinity (KA1 = 2.4 +/- 0.6 X 10(9) M-1), low capacity (N1 = 7.8 +/- 0.8 fmoles/mg of protein) and a second site low affinity (KA2 = 9.6 +/- 0.6 X 10(6) M-1) and high capacity (N2 = 219 +/- 128 fmoles/mg of protein). Analysis of competition by Sar1-Ile8 angiotensin II for 125I-angiotensin II binding sites indicated that the antagonist interacted with the first site with high affinity (KA1 = 8 X 10(9) M- 1), but interacted minimally with the second site (KA2 = 10(5) M-1). Monovalent cations (Na+, K+, Li+, NH4+) were roughly equipotent in decreasing 125I-angiotensin II binding by reducing the number of high- affinity sites (N1 = 2.6 +/- 0.7 fmoles/mg of protein with 100 mM Na+) without changing the affinity of either site or the number of low- affinity sites. The number of high-affinity sites was increased to 14.4 +/- 1.5 fmoles/mg of protein by 5 mM Mg2+. In the presence of divalent cations, nucleotides reduced binding of 125I-angiotensin II with the potency order guanosyl-5'-yl-imidodiphosphate greater than GTP greater than GDP greater than ATP greater than GMP. Guanosyl-5'yl- imidodiphosphate significantly reduced the affinity of the high- affinity site (KA1 = 1.0 +/- 0.2 X 10(9) M-1) and perhaps of the low- affinity site (KA2 = 1.0 +/- 2.2 X 10(6) M-1). Computer-assisted assessment of dissociation of 0.3 nM 125I-angiotensin II from rabbit myocardial membranes corroborated the equilibrium data: dissociation was biphasic (K-1 = 0.19 +/- 0.2 min-1 for a rapidly dissociating site, k-1 = 2.5 +/- 2.1 X 10(-3) min-1 for a slowly dissociating site); 5 mM Mg2+ did not significantly change either dissociation rate; but guanosyl-5'-yl-imidodiphosphate significantly increased dissociation rates from both sites. Despite the indirect evidence that these angiotensin II receptors interact with guanine nucleotide regulatory proteins, angiotensin II (10(-6) M) failed to influence adenylate cyclase activity. The physiological implications of the presence in ventricular myocardium of two distinct angiotensin II receptors and in particular the implications of a receptor-associated guanine nucleotide regulatory protein which does not couple to adenylate cyclase require further investigation.

Volume 24, Issue 2, pp. 213-221, 09/01/1983
Copyright © 1983 by American Society for Pharmacology and Experimental Therapeutics

This article has been cited by other articles:

				D. M. Browe and C. M. Baumgarten Angiotensin II (AT1) Receptors and NADPH Oxidase Regulate Cl- Current Elicited by {beta}1 Integrin Stretch in Rabbit Ventricular Myocytes J. Gen. Physiol., August 30, 2004; 124(3): 273 - 287. [Abstract] [Full Text] [PDF]

				K. Obayashi, M. Horie, L.-H. Xie, K. Tsuchiya, A. Kubota, H. Ishida, and S. Sasayama Angiotensin II Inhibits Protein Kinase A–Dependent Chloride Conductance in Heart via Pertussis Toxin–Sensitive G Proteins Circulation, January 7, 1997; 95(1): 197 - 204. [Abstract] [Full Text]

				J. R Libonati, F. R Eberli, H. W Sesselberg, and C. S Apstein Effects of low-flow ischemia on the positive inotropic action of angiotensin II in isolated rabbit and rat hearts Cardiovasc Res, January 1, 1997; 33(1): 71 - 81. [Abstract] [Full Text] [PDF]

				V. Regitz-Zagrosek, N. Friedel, A. Heymann, P. Bauer, M. Neuß, A. Rolfs, C. Steffen, A. Hildebrandt, R. Hetzer, and E. Fleck Regulation, Chamber Localization, and Subtype Distribution of Angiotensin II Receptors in Human Hearts Circulation, March 1, 1995; 91(5): 1461 - 1471. [Abstract] [Full Text]