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Human heart beta-adrenoceptors: beta1-adrenoceptor diversification through 'affinity states' and polymorphism
P Molenaar1, L Chen, A B T Semmler
1Department of Medicine, The University of Queensland, The Prince Charles Hospital, Chermside, Queensland, Australia. p.molenaar@uq.edu.au
Beta-adrenoceptors in the heart activate signaling pathways for contraction and relaxation. Studies reveal two affinity states of the beta(1)-adrenoceptor and their varying response to beta-blockers, influencing heart failure treatment outcomes.
Area of Science:
- Cardiology
- Pharmacology
- Molecular Biology
Background:
- Beta(1)- and beta(2)-adrenoceptors in the human heart mediate increases in contractile force and relaxation.
- Activation involves G(salpha)-protein, not G(ialpha)-protein, leading to protein kinase A-catalyzed phosphorylation.
- Two affinity states of the beta(1)-adrenoceptor (beta(1H) and beta(1L)) have been identified, differing in their affinity for beta-blockers.
Purpose of the Study:
- To investigate the functional roles of beta(1)- and beta(2)-adrenoceptors in the human heart.
- To characterize the two affinity states of the beta(1)-adrenoceptor (beta(1H) and beta(1L)).
- To examine the impact of beta(1)-adrenoceptor polymorphisms on the effectiveness of carvedilol treatment in heart failure patients.
Main Methods:
- Studies in human atrial and ventricular tissue.
- Use of beta(1)-/beta(2)-adrenoceptor double-knockout and beta(2)-adrenoceptor-knockout mice.
- Analysis of left ventricular ejection fraction (LVEF) in heart failure patients treated with carvedilol, stratified by beta(1)-adrenoceptor polymorphisms (Arg49Gly and Ser389Gly).
Main Results:
- Both beta(1)- and beta(2)-adrenoceptors couple to G(salpha)-protein.
- The beta(1H)-adrenoceptor is activated by noradrenaline and blocked with high affinity by beta-blockers.
- The beta(1L)-adrenoceptor is activated by drugs like (-)-CGP 12177 and (-)-pindolol and blocked with low affinity by beta-blockers.
- Carvedilol improved LVEF in patients with non-ischaemic cardiomyopathy, with greater improvement observed in patients with the Arg389 allele (Arg389Arg > Arg389Gly > Gly389Gly).
Conclusions:
- The human heart expresses both beta(1)- and beta(2)-adrenoceptors coupled to G(salpha)-protein.
- The beta(1)-adrenoceptor exists in two affinity states, beta(1H) and beta(1L), influencing its interaction with beta-blockers.
- Beta(1)-adrenoceptor polymorphisms, particularly at position 389, affect the response to carvedilol therapy in heart failure, suggesting a role in personalized medicine.
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