PT  - JOURNAL ARTICLE
AU  - Y Nozawa
AU  - A Haruno
AU  - N Oda
AU  - Y Yamasaki
AU  - N Matsuura
AU  - S Yamada
AU  - K Inabe
AU  - R Kimura
AU  - H Suzuki
AU  - T Hoshino
TI  - Angiotensin II receptor subtypes in bovine and human ventricular myocardium.
DP  - 1994 Aug 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 566--571
VI  - 270
IP  - 2
4099  - http://jpet.aspetjournals.org/content/270/2/566.short
4100  - http://jpet.aspetjournals.org/content/270/2/566.full
SO  - J Pharmacol Exp Ther1994 Aug 01; 270
AB  - Angiotensin II (AII) binding sites in bovine and human ventricular myocardium were characterized by a radioreceptor assay. The specific binding of [125I]AII to myocardial membranes appeared to be saturable, and it was of high affinity with apparent dissociation constants of 1.60 nM (bovine) and 1.09 nM (human). The Bmax values were 39.7 fmol/mg protein (bovine) and 6.07 fmol/mg protein (human). Both losartan (angiotensin type 1 receptor subtype selective antagonist) and PD123177 (the angiotensin type 2 receptor subtype selective antagonist) inhibited specific [125I]AII binding to bovine myocardium, and their Hill coefficients were less than unity. Nonlinear least-squares regression analysis has suggested the existence of two populations of [125I]AII binding sites that have high and low affinity for losartan or PD123177. The relative proportions of high- and low-affinity sites for losartan in bovine myocardium were 68% and 32%, and those for PD123177 were 33% and 67%, respectively. On the other hand, specific [125I]AII binding in human myocardium was inhibited by losartan with much lower affinity and also by PD123177 with higher affinity, compared with bovine myocardium. The Hill coefficients for both drugs were close to one. Dithiothreitol enhanced specific [125I]AII binding to bovine myocardium in the presence of losartan, but it reduced [125I]AII binding in the presence of PD123177. This agent markedly enhanced specific [125I]AII binding to human myocardium. Thus, it is possible that bovine myocardium has both angiotensin type 1 receptor and the angiotensin type 2 receptor subtypes of AII receptors whereas human myocardium has predominantly the angiotensin type 2 receptor subtype.