TY - JOUR T1 - Novel Paradigms Governing <em>β</em><sub>1</sub>-Adrenergic Receptor Trafficking in Primary Adult Rat Cardiac Myocytes JF - Molecular Pharmacology JO - Mol Pharmacol SP - 862 LP - 875 DO - 10.1124/mol.118.112045 VL - 94 IS - 2 AU - Mohammed M. Nooh AU - Salvatore Mancarella AU - Suleiman W. Bahouth Y1 - 2018/08/01 UR - http://molpharm.aspetjournals.org/content/94/2/862.abstract N2 - The β1-adrenergic receptor (β1-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 β1-AR into endosomes and their removal promotes the recycling of the endosomal β1-AR back to the plasma membrane; however, whether these redistributive processes occur in terminally differentiated cells is unknown. Compartmentalization of the β1-AR in response to β-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 β1-AR was expressed on the external membrane (the sarcolemma) of cardiomyocytes. Exposing ARVMs to isoproterenol redistributed surface β1-ARs into small (∼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 β-agonist with the β-blocker alprenolol, induced the translocation of the wild-type β1-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 β1-AR, which is phosphorylated by a pool of cAMP-dependent protein kinases anchored at the type-1 PDZ of the β1-AR. These data show that redistribution of the β1-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 β1-AR signaling under normal or pathologic conditions. ER -