Binding of the antagonist [3H]candesartan to angiotensin II AT1 receptor-transfected [correction of tranfected] Chinese hamster ovary cells |
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Authors: | Fierens F Vanderheyden P M De Backer J P Vauquelin G |
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Affiliation: | Department of Molecular and Biochemical Pharmacology, Free University of Brussels (VUB), Sint-Genesius Rode, Belgium. |
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Abstract: | Binding of the non-peptide angiotensin II AT1 antagonist 3H](2-ethoxy-1-(2'-(1H-tetrazol-5-yl)biphenyl-4-yl)methyl]- H-benzimidazoline-7-carboxylic acid (3H]candesartan) to human angiotensin II AT1 receptor-transfected Chinese hamster ovary (CHO-AT1) cells was inhibited to the same extent by angiotensin II and non-peptide angiotensin II AT1 antagonists. No binding was observed in control CHO-K1 cells. Dissociation was slow (k(-1) = 0.0010+/-0.0001 min(-1)) after removal of the free 3H]candesartan but increased 5-fold upon addition of supramaximal concentrations of angiotensin II AT1 antagonists. Angiotensin II responses recovered equally slow from candesartan-pretreatment. When washed and further incubated, these angiotensin II responses also recovered more rapidly in the presence of 2-n-butyl-4-chloro-5-hydroxymethyl-1-(2'-(1H-tetrazol-5-yl)biphen yl-4-yl)methyl]imidazole (losartan), indicating that unlabelled ligands prevented reassociation. 3 H]candesartan saturation binding experiments required a long time to reach equilibrium. Therefore, the equilibrium dissociation constant (Kd = 51+/-8 pM) was calculated from the association and dissociation rate constants. Our findings indicate that the insurmountable nature of candesartan in functional studies is related to its slow dissociation from the receptor. |
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