Effect of saponin and filipin on antagonist binding to AT 1 receptors in intact cells.
In the present study, [ 3H ]-candesartan binding experiments were performed on intact Chinese Hamster Ovary cells transfected with the human AT1 receptor (CHO-AT1 cells). Cells were pre-treated with 0.01mg/ml saponin or filipin. Both pre-treatments resulted in an increased dissociation rate and decreased affinity of the insurmountable non-peptide antagonist [3H ]-candesartan. A similar decrease in affinity was observed for the peptide antagonist Sar1-Ile8 angiotensin II and for other non-peptide antagonists, irrespectively of their degree of insurmountability. A similar discrepancy in [ 3H ]-candesartan binding was earlier observed when comparing intact CHO-AT1 cells and membrane preparations thereof. This similarity is further highlighted by the observations that saponin or filipin no longer affect [ 3H ]-candesartan binding to CHO-AT1 cell membranes and that both agents permeabilise the CHO-AT1 cells. This suggests that the intracellular composition and/or organisation of living cells play an active role with regard to antagonist-AT1 receptor interactions.
Verheijen
Ilse
I
Department of Molecular and Biochemical Pharmacology, Free University of Brussels (VUB), Pleinlaan 2, 1050 Brussels, Belgium. iverheij@vub.ac.be.
Tourlousse
Dieter
D
Vanderheyden
Patrick M L
PM
Backer
Jean-Paul De
JP
Vauquelin
Georges
G
D000804:Angiotensin II / Q000378:metabolism; D047228:Angiotensin II Type 1 Receptor Blockers; D000818:Animals; D001562:Benzimidazoles / Q000494:pharmacology*; D001667:Binding, Competitive; D001713:Biphenyl Compounds; D016466:CHO Cells; D006224:Cricetinae; D004347:Drug Interactions; D005260:Female; D005372:Filipin / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D011869:Radioligand Assay; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism; D012503:Saponins / Q000494:pharmacology*; D013777:Tetrazoles / Q000494:pharmacology*; D014162:Transfection
D047228:Angiotensin II Type 1 Receptor Blockers; D001562:Benzimidazoles; D001713:Biphenyl Compounds; D044140:Receptor, Angiotensin, Type 1; D012503:Saponins; D013777:Tetrazoles; D000804:Angiotensin II; D005372:Filipin; C081643:candesartan