title: Inhibition of type 1 protein phosphatase activity by activation of beta-adrenoceptors in ventricular myocardium.
abstract: The regulation of protein phosphatase (PP) activity by cardiac beta-adrenergic receptor stimulation with isoproterenol (ISO) was studied in four groups of guinea pigs consisting of seven animals each. Group 1 received the vehicle solution only intraperitoneally; group 2, 6 microg/kg of ISO; group 3, 60 microg/kg of ISO; and group 4, 600 microg/kg of ISO. Total PP activity (consisting of both type 1 and type 2A PP), activity of each PP subtype, the cAMP-dependent protein kinase activity ratio (-cAMP/+cAMP), the phosphorylation of PP inhibitor 1, and the phosphorylation of phospholamban were measured in ventricular tissue. PP activity was also studied in ventricular cardiomyocytes isolated from guinea pigs treated with and without 1 microM ISO or 1 microM ISO plus 10 microM propranolol, an antagonist of the beta-adrenoceptor. PP activity decreased significantly in membrane vesicles, but not in cytosolic fractions, of guinea pigs treated with 60 and 600 microg/kg of ISO compared with untreated animals. The PKA activity ratio, PLB phosphorylation, and PP inhibitor 1 phosphorylation increased in ventricles of guinea pigs treated with 60 and 600 microg/kg of ISO compared with vehicle-treated animals. The decrease in overall PP activity was due primarily to a reduction in type 1 but not type 2A PP activity. In isolated ventricular cardiomyocytes, PP activity was decreased significantly after treatment with 1 microM ISO, and this inhibition was reversed by treatment with 10 microM propranolol. The membrane vesicles of group 1 animals did not release any catalytic subunit of type 1 PP upon phosphorylation by exogenous PKA. These results indicate that activation of cardiac beta-adrenoceptors inhibits type 1 PP activity via phosphorylation of PP inhibitor 1 in the ventricles. This effect is associated with the well-known effect of ISO on increases in the PKA activity ratio and PLB phosphorylation. Inhibition of type 1 PP activity could be one possible mechanism, in addition to activation of adenylate cyclase, by which ISO mediates enhanced contractility of the heart.
authors.affiliation: Department of Medicine, Division of Cardiovascular Medicine, Henry Ford Heart and Vascular Institute, Henry Ford Hospital, 2799 West Grand Boulevard, Detroit, MI 48202, USA. rgupta1@hfhs.org
authors.forename: Ramesh C
authors.initials: RC
authors.lastname: Gupta
authors.forename: John
authors.initials: J
authors.lastname: Neumann
authors.forename: August M
authors.initials: AM
authors.lastname: Watanabe
authors.forename: Hani N
authors.initials: HN
authors.lastname: Sabbah
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002352:Carrier Proteins; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009206:Myocardium / Q000201:enzymology* / Q000378:metabolism; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D011506:Proteins / Q000494:pharmacology; D016601:RNA-Binding Proteins / Q000378:metabolism; D011943:Receptors, Adrenergic, beta / Q000378:metabolism*; D000099211:Phospholamban; D000097847:Protein Phosphatase Inhibitory Proteins
chemical_list: D000318:Adrenergic beta-Agonists; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D007545:Isoproterenol; D010749:Phosphoprotein Phosphatases; D011506:Proteins; D016601:RNA-Binding Proteins; D011943:Receptors, Adrenergic, beta; D000099211:Phospholamban; C021042:protein phosphatase inhibitor-1; C024833:protein phosphatase inhibitor-2; D000097847:Protein Phosphatase Inhibitory Proteins