Abstract
β1- and β3-adrenergic receptors (AR) are the predominant β-AR subtypes in adipocytes, and analysis of native and recombinant β-AR has revealed several pharmacological and biochemical differences between these subtypes. This study used chimeric and mutated rat β-AR expressed in Chinese hamster ovary cells to examine the basis of certain characteristic differences in the agonist properties of catecholamines and prototypic β3-AR agonists. The exchange of sequence beyond transmembrane (TM) region 6 between the β-AR subtypes had dramatic and reciprocal effects on the affinity and efficacy of the prototypic β3-AR agonists BRL 37,344 and CL 316,243, without affecting the interactions with catecholamines. Mutation of Phe350 and Phe351 in TM7 of the β1-AR to Ala and Leu found in the β3-AR was sufficient to allow activation by prototypic β3-AR agonists. Interestingly, this mutation did not affect catecholamine action and it did not impair the ability of propranolol to block the actions of isoproterenol or the selective β3-AR agonists. β1-AR containing β3-AR sequence from predicted TM5 through TM6 exhibited reduced affinity for catecholamines without altering agonist potency, suggesting enhanced coupling efficiency. Inclusion of the homologous β1-AR sequence in the β3-AR, however, did not produce reciprocal effects. These results are the first to define a major determinant of β3-AR subtype-selective agonism in TM7 and demonstrate that the determinants of selective phenethanolamines, catecholamines, and propranolol action are distinct.
Footnotes
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Send reprint requests to: Dr. James Granneman, 2309 Scott Hall of Basic Medical Sciences, Wayne State University School of Medicine, Detroit, MI 48201. E-mail:jgranne{at}med.wayne.edu
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This work was supported by United States Public Health Service Grant DK46339.
- Abbreviations:
- AR
- adrenergic receptors
- ISO
- (−)-isoproterenol
- CL
- CL 316,243
- BRL
- BRL 37,344
- CYP
- cyanopindolol
- TM
- transmembrane
- CHO
- Chinese hamster ovary
- NE
- (−)-norepinephrine
- DOB
- (±)-dobutamine
- Received November 11, 1997.
- Accepted January 27, 1998.
- The American Society for Pharmacology and Experimental Therapeutics
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