Agonist potency at the cloned human beta-3 adrenoceptor depends on receptor expression level and nature of assay
The cloned human beta-3 adrenoceptor was expressed in Chinese hamster ovary cells at three different levels (130, 400 and 3000 fmol/mg). The potency and intrinsic activity of a range of agonists in functional assays with these cell lines rose as a function of increasing receptor density. Operational...
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Published in | The Journal of pharmacology and experimental therapeutics Vol. 279; no. 1; pp. 214 - 221 |
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Main Authors | , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
United States
American Society for Pharmacology and Experimental Therapeutics
01.10.1996
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Subjects | |
Online Access | Get full text |
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Summary: | The cloned human beta-3 adrenoceptor was expressed in Chinese hamster ovary cells at three different levels (130, 400 and
3000 fmol/mg). The potency and intrinsic activity of a range of agonists in functional assays with these cell lines rose as
a function of increasing receptor density. Operational analysis of concentration-response data allowed calculation of functional
affinity and efficacy of agonists at the human beta-3 adrenoceptor. The data highlighted the low efficacy of BRL 37344 ¿(RR,SS)-(+/-)-4-[(2-(2-(3-chlorophenyl)-2-hydroxyethyl)amino)-propyl]
phenoxyacetate¿ for the human beta-3 adrenoceptor, which may explain its lower potency at the human receptor despite its higher
affinity relative to isoprenaline. The potency of catecholamines at the human beta-3 adrenoceptor was found to be 1 to 2 orders
of magnitude higher when determined in an intact cell cAMP accumulation assay compared with a membrane-based adenylyl cyclase
activation assay. The reason for this enhanced sensitivity is not clear, but the result is that the potency of the natural
agonist noradrenaline in the intact cell is considerably higher than predicted either from its ligand binding affinity, or
from its potency in membrane-based assays. Much smaller enhancements in sensitivity were observed for compounds of the aryloxypropanolamine
class such as CGP 12177 [(+/-)-4-(3-t-butylamino-2-hydroxypropoxy)benzimidazol-2-one], with the result that the rank order
of potency of such agonists at the beta-3 adrenoceptor was altered. In particular, CGP 12177 exhibited high relative potency
in the cyclase assay, but low relative potency in intact cell assays. These findings highlight the importance of selecting
appropriate expression levels and appropriate assay methodology when cloned receptors are used to characterize agonists. |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 ObjectType-Article-1 ObjectType-Feature-2 |
ISSN: | 0022-3565 1521-0103 |