title: G protein-coupled receptor kinase 5 regulates airway responses induced by muscarinic receptor activation.
abstract: G protein-coupled receptors (GPCRs) transduce extracellular signals into intracellular events. The waning responsiveness of GPCRs in the face of persistent agonist stimulation, or desensitization, is a necessary event that ensures physiological homeostasis. GPCR kinases (GRKs) are important regulators of GPCR desensitization. GRK5, one member of the GRK family, desensitizes central M(2) muscarinic receptors in mice. We questioned whether GRK5 might also be an important regulator of peripheral muscarinic receptor responsiveness in the cardiopulmonary system. Specifically, we wanted to determine the role of GRK5 in regulating muscarinic receptor-mediated control of airway smooth muscle tone or regulation of cholinergic-induced bradycardia. Tracheal pressure, heart rate, and tracheal smooth muscle tension were measured in mice having a targeted deletion of the GRK5 gene (GRK5(-/-)) and littermate wild-type (WT) control mice. Both in vivo and in vitro results showed that the airway contractile response to a muscarinic receptor agonist was not different between GRK5(-/-) and WT mice. However, the relaxation component of bilateral vagal stimulation and the airway smooth muscle relaxation resulting from beta(2)-adrenergic receptor activation were diminished in GRK5(-/-) mice. These data suggest that M(2) muscarinic receptor-mediated opposition of airway smooth muscle relaxation is regulated by GRK5 and is, therefore, excessive in GRK5(-/-) mice. In addition, this study shows that GRK5 regulates pulmonary responses in a tissue- and receptor-specific manner but does not regulate peripheral cardiac muscarinic receptors. GRK5 regulation of airway responses may have implications in obstructive airway diseases such as asthma or chronic obstructive pulmonary disease.
authors.affiliation: Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA. walke082@mc.duke.edu
authors.forename: J K L
authors.initials: JK
authors.lastname: Walker
authors.forename: R R
authors.initials: RR
authors.lastname: Gainetdinov
authors.forename: D S
authors.initials: DS
authors.lastname: Feldman
authors.forename: P K
authors.initials: PK
authors.lastname: McFawn
authors.forename: M G
authors.initials: MG
authors.lastname: Caron
authors.forename: R J
authors.initials: RJ
authors.lastname: Lefkowitz
authors.forename: R T
authors.initials: RT
authors.lastname: Premont
authors.forename: J T
authors.initials: JT
authors.lastname: Fisher
mesh_terms: D000818:Animals; D001993:Bronchodilator Agents / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D004558:Electric Stimulation; D054774:G-Protein-Coupled Receptor Kinase 5; D015870:Gene Expression; D006339:Heart Rate; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation / Q000502:physiology; D010275:Parasympathetic Nervous System / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D043585:Receptor, Muscarinic M2 / Q000378:metabolism*; D043587:Receptor, Muscarinic M3 / Q000378:metabolism*; D014132:Trachea / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D014630:Vagus Nerve / Q000502:physiology
chemical_list: D001993:Bronchodilator Agents; D018679:Cholinergic Agonists; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; D002217:Carbachol; D017346:Protein Serine-Threonine Kinases; D054774:G-Protein-Coupled Receptor Kinase 5; C517895:Grk5 protein, mouse; D007545:Isoproterenol