title: Duality of G protein-coupled mechanisms for beta-adrenergic activation of NKCC activity in skeletal muscle.
abstract: Skeletal muscle Na(+)-K(+)-2Cl(-) cotransporter (NKCC) activity provides a potential mechanism for regulated K(+) uptake. beta-Adrenergic receptor (beta-AR) activation stimulates skeletal muscle NKCC activity in a MAPK pathway-dependent manner. We examined potential G protein-coupled pathways for beta-AR-stimulated NKCC activity. Inhibition of G(s)-coupled PKA blocked isoproterenol-stimulated NKCC activity in both the slow-twitch soleus muscle and the fast-twitch plantaris muscle. However, the PKA-activating agents cholera toxin, forskolin, and 8-bromo-cAMP (8-BrcAMP) were not sufficient to activate NKCC in the plantaris and partially stimulated NKCC activity in the soleus. Isoproterenol-stimulated NKCC activity in the soleus was abolished by pretreatment with pertussis toxin (PTX), indicating a G(i)-coupled mechanism. PTX did not affect the 8-BrcAMP-stimulated NKCC activity. PTX treatment also precluded the isoproterenol-mediated ERK1/2 MAPK phosphorylation in the soleus, consistent with NKCC's MAPK dependency. Inhibition of isoproterenol-stimulated ERK activity by PTX treatment was associated with an increase in Akt activation and phosphorylation of Raf-1 on the inhibitory residue Ser(259). These results demonstrate a novel, muscle phenotype-dependent mechanism for beta-AR-mediated NKCC activation that involves both G(s) and G(i) protein-coupled mechanisms.
authors.affiliation: Department of Physiology, College of Medicine, University of Tennessee Health Science Center, 894 Uniuon Avenue, Memphis, TN 38163, USA.
authors.forename: Aidar R
authors.initials: AR
authors.lastname: Gosmanov
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Wong
authors.forename: Donald B
authors.initials: DB
authors.lastname: Thomason
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D020536:Enzyme Activators / Q000494:pharmacology; D005260:Female; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D066298:In Vitro Techniques; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D037342:Pertussis Toxin; D010766:Phosphorylation / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D028021:Sodium-Potassium-Chloride Symporters / Q000187:drug effects / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D000318:Adrenergic beta-Agonists; D020536:Enzyme Activators; D011518:Proto-Oncogene Proteins; D011943:Receptors, Adrenergic, beta; D028021:Sodium-Potassium-Chloride Symporters; D010566:Virulence Factors, Bordetella; D015124:8-Bromo Cyclic Adenosine Monophosphate; D037342:Pertussis Toxin; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf; D017868:Cyclic AMP-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D019204:GTP-Binding Proteins; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D019205:GTP-Binding Protein alpha Subunits, Gs