期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2004
卷号：101
期号：18
页码：7082-7087
DOI：10.1073/pnas.0308335101
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Catecholaminergic activation of myocardial {beta}-adrenergic receptors ({beta}AR) is the principle mechanism regulating cardiac function. Agonists desensitize {beta}AR through G protein-coupled receptor kinase-mediated uncoupling and {beta}-arrestin-mediated internalization. Although inhibition of myocardial G protein-coupled receptor kinase-2 enhances cardiac function and reverses heart failure, pathophysiological effects of modulated {beta}AR internalization/recycling are unknown. We used mutation and transgenic expression of Rab4, which regulates vesicular transport of heptahelical receptors to plasma membranes, to interrogate in vivo {beta}AR trafficking and cardiac function. Expression of constitutively active Rab4 Q72L had no effects on cardiac structure or function, but dominant inhibitor Rab4 S27N impaired responsiveness to endogenous and exogenous catecholamines. To relate {beta}AR trafficking to diminished cardiac function, Rab4 mutant mice were crossbred with mice overexpressing human {beta}2AR. In unstimulated {beta}2AR overexpressors, {beta}2AR localized to heavier endosomes and translocated to lighter, caveolin-rich fractions after isoproterenol stimulation. Coexpression of {beta}2AR with activated Rab4 Q72L caused loss of receptors from heavier endosomes while retaining normal inotropy. In contrast, coexpression of {beta}2AR with inhibitory Rab4 S27N mimicked isoproterenol-induced receptor redistribution to caveolae, with diminished cardiac inotropy. Rab4 inhibition alone prevented resensitization after isoproterenol-induced in vivo adrenergic desensitization. Confocal and ultrastructural analyses revealed bizarre vesicular structures and abnormal accumulation of {beta}2AR in the sarcoplasm and subsarcollema of Rab4 S27N, but not Q72L, mice. These data provide evidence for constant bidirectional sarcollemal-vesicular {beta}AR trafficking in the in vivo heart and show that Rab4-mediated recycling of internalized {beta}AR is necessary for normal cardiac catecholamine responsiveness and resensitization after agonist exposure.
