科研之友
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摘要
The beta(1)-adrenergic receptor (beta(1)-AR) is a major cardiac G protein-coupled receptor, which mediates cardiac actions of catecholamines and is involved in genesis and treatment of numerous cardiovascular disorders. In mammalian cells, catecholamines induce the internalization of the beta(1)-AR into endosomes and their removal promotes the recycling of the endosomal beta(1)-AR back to the plasma membrane; however, whether these redistributive processes occur in terminally differentiated cells is unknown. Compartmentalization of the beta(1)-AR in response to beta-agonists and antagonists was determined by confocal microscopy in primary adult rat ventricular myocytes (ARVMs), which are terminally differentiated myocytes with unique structures such as transverse tubules (T-tubules) and contractile sarcomeres. In unstimulated ARVMs, the fluorescently labeled beta(1)-AR was expressed on the external membrane (the sarcolemma) of cardiomyocytes. Exposing ARVMs to isoproterenol redistributed surface beta(1)-ARs into small (similar to 225-250 nm) regularly spaced internal punctate structures that overlapped with puncta stained by Di-8 ANEPPS, a membrane-impermeant T-tubule-specific dye. Replacing the beta-agonist with the beta-blocker alprenolol, induced the translocation of the wild-type beta(1)-AR from these punctate structures back to the plasma membrane. This step was dependent on two barcodes, namely, the type-1 PDZ binding motif and serine at position 312 of the beta(1)-AR, which is phosphorylated by a pool of cAMP-dependent protein kinases anchored at the type-1 PDZ of the beta(1)-AR. These data show that redistribution of the beta(1)-AR in ARVMs from internal structures back to the plasma membrane was mediated by a novel sorting mechanism, which might explain unique aspects of cardiac beta(1)-AR signaling under normal or pathologic conditions.
- 出版日期2018-8-1
