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Distinction between surmountable and insurmountable selective AT 1 receptor antagonists by use of CHO‐K1 cells expressing human angiotensin II AT 1 receptors
Author(s) -
Vanderheyden P M L,
Fierens F L P,
De Backer J P,
Fraeyman N,
Vauquelin G
Publication year - 1999
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1038/sj.bjp.0702398
Subject(s) - losartan , candesartan , angiotensin ii , angiotensin ii receptor type 1 , chemistry , irbesartan , medicine , receptor , endocrinology , angiotensin receptor , pharmacology , biochemistry , biology , blood pressure
CHO‐K1 cells that were stably transfected with the gene for the human AT 1 receptor (CHO‐AT 1 cells) were used for pharmacological studies of non‐peptide AT 1 receptor antagonists. In the presence of 10 m M LiCl, angiotensin II caused a concentration‐dependent and long‐lasting increase of inositol phosphates accumulation with an EC 50 of 3.4 n M . No angiotensin II responses are seen in wild‐type CHO‐K1 cells. [ 3 H]‐Angiotensin II bound to cell surface AT 1 receptors (dissociates under mild acidic conditions) and is subject to rapid internalization. Non‐peptide selective AT 1 antagonists inhibited the angiotensin II (0.1 μ M ) induced IP accumulation and the binding of [ 3 H]‐angiotensin II (1 n M ) with the potency order: candesartan > EXP3174 > irbesartan > losartan. Their potencies are lower in the presence of bovine serum albumin. Preincubation with the insurmountable antagonist candesartan decreased the maximal angiotensin II induced inositol phosphate accumulation up to 94% and, concomitantly, decreased the maximal binding capacity of the cell surface receptors. These inhibitory effects were half‐maximal for 0.6 n M candesartan and were attenuated by simultaneous preincubation with 1 μ M losartan indicating a syntopic action of both antagonists. Losartan caused a parallel rightward shift of the angiotensin II concentration‐response curves and did not affect the maximal binding capacity. EXP3174 (the active metabolite of losartan) and irbesartan showed a mixed‐type behavior in both functional and binding studies. Reversal of the inhibitory effect was slower for candesartan as compared with EXP3174 and irbesartan and it was almost instantaneous for losartan, suggesting that the insurmountable nature of selective AT 1 receptor antagonists in functional studies was related to their long‐lasting inhibition.British Journal of Pharmacology (1999) 126 , 1057–1065; doi: 10.1038/sj.bjp.0702398