The β-adrenergic receptors

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Item Type:	Article
Title:	The β-adrenergic receptors
Creators Name:	Wallukat, G.
Abstract:	Background: The {beta}-adrenergic receptors of the myocardium play an important role in the regulation of heart function. The {beta}-adrenergic receptors belong to the family of G-protein coupled receptors. Three subtypes have been distinguished ({beta}1-, {beta}2-, and {beta}3-adrenoceptors). The receptors consist of seven membrane-spanning domains, three intra- and three extracellular loops, one extracellular N-terminal domain, and one intracellular C-terminal tail. Pathophysiology: Stimulation of {beta}-adrenergic receptors by catecholamines is realized via the {beta}-adrenoceptor-adenylylcyclase-protein kinase A cascade. The second messenger is the cyclic AMP (cAMP). Stimulation of the cascade caused an accumulation of the second messenger cAMP and activated via the cAMP the cAMP dependent protein kinase A (PKA) The PKA phosphorylated, beside other cell proteins, the {beta}-adrenergic receptors. A phosphorylation of the {beta}-adrenergic receptors caused - with exception of the {beta}3-adrenoceptor - an uncoupling and desensitisation of the receptors. Phosphorylation via the G-protein receptor kinase (GRK or {beta}ARK) also caused uncoupling and reduced the {beta}-adrenergic responsiveness. The uncoupling of the receptor is the prerequisite for receptor internalisation. In the process of internalisation the receptor shifted from the sarcolemma membrane into cytosolic compartments. Chronic {beta}-adrenergic stimulation caused a down-regulation of the receptors. During this process of desensitisation the expression of the receptor on mRNA and protein level is reduced. Changing of the Receptors in the Failing Heart: In patients with dilated cardiomyopathy the {beta}-adrenergic responsiveness of the myocard is diminished. It was shown that in these patients the expression of the {beta}1-adrenergic receptor is reduced on the mRNA and protein level. In these patients the expression of the inhibitory G-protein Gi is increased. Furthermore, the expression of the G-protein receptor kinase is elevated. This kinase induces the uncoupling of the {beta}-adrenergic receptors. These alterations of the {beta}-adrenoceptor signal cascade may be induced by an elevated catecholamine release or by agonist-like autoantibodies directed against the {beta}1-adrenergic receptor found in patients with dilated cardiomyopathy. Both, permanent stimulation with catecholamines and chronic treatment with agonistic anti-{beta}1-adrenoceptor autoantibodies cause a reduction of the expression of the {beta}1-adrenoceptor on mRNA and protein level in "in vitro" experiments. Moreover, an over-expression of the {beta}1-adrenoceptor, the stimulatory Gs protein, and the protein kinase A induce detrimental alterations of the cardiac function and morphology in transgenic animals. These animals developed heart failure accompanied by an increased mortality rate.
Keywords:	Beta-Adrenoceptor, Desensitisation, Dilatative Cardiomyopathy, Embryonic Stem Cells, Overexpression
Source:	Herz
ISSN:	0340-9937
Publisher:	Urban & Vogel
Volume:	27
Number:	7
Page Range:	683-690
Date:	November 2002
Official Publication:	https://doi.org/10.1007/s00059-002-2434-z
PubMed:	View item in PubMed

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