title: Cyclic GMP protein kinase activity is reduced in thyroxine-induced hypertrophic cardiac myocytes.
abstract: 1. We tested the hypothesis that the cGMP-dependent protein kinase has major negative functional effects in cardiac myocytes and that the importance of this pathway is reduced in thyroxine (T4; 0.5 mg/kg per day for 16 days) hypertrophic myocytes. 2. Using isolated ventricular myocytes from control (n = 7) and T4-treated (n = 9) rabbit hypertrophic hearts, myocyte shortening was studied with a video edge detector. Oxygen consumption was measured using O2 electrodes. Protein phosphorylation was measured autoradiographically. 3. Data were collected following treatment with: (i) 8-(4-chlorophenylthio)guanosine-3',5'-monophosphate (PCPT; 10-7 or 10-5 mol/L); (ii) 8-bromo-cAMP (10-5 mol/L) followed by PCPT; (iii) beta-phenyl-1,N2-etheno-8-bromoguanosine-3',5'-monophosphorothioate, SP-isomer (SP; 10-7 or 10-5 mol/L); or (iv) 8-bromo-cAMP (10-5 mol/L) followed by SP. 4. There were no significant differences between groups in baseline percentage shortening (Pcs; 4.9 +/- 0.2 vs 5.6 +/- 0.4% for control and T4 groups, respectively) and maximal rate of shortening (Rs; 64.8 +/- 5.9 vs 79.9 +/- 7.1 micro m/ s for control and T4 groups, respectively). Both SP and PCPT decreased Pcs (-43 vs-21% for control and T4 groups, respectively) and Rs (-36 vs-22% for control and T4 groups, respectively), but the effect was significantly reduced in T4 myocytes. 8-Bromo-cAMP similarly increased Pcs (28 vs 23% for control and T4 groups, respectively) and Rs (20 vs 19% for control and T4 groups, respectively). After 8-bromo-cAMP, SP and PCPT decreased Pcs (-34%) and Rs (-29%) less in the control group. However, the effects of these drugs were not altered in T4 myocytes (Pcs -24%; Rs -22%). Both PCPT and cAMP phosphorylated the same five protein bands. In T4 myocytes, these five bands were enhanced less. 5. We conclude that, in control ventricular myocytes, the cGMP-dependent protein kinase exerted major negative functional effects but, in T4-induced hypertrophic myocytes, the importance of this pathway was reduced and the interaction between cAMP and the cGMP protein kinase was diminished.
authors.affiliation: Heart and Brain Circulation Laboratory, Departments of Physiology & Biophysics and Surgery, University of Medicine and Dentistry of New Jersey - Robert Wood Johnson Medical School, Piscataway, New Jersey 08854-5635, USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Yan
authors.forename: Qihang
authors.initials: Q
authors.lastname: Zhang
authors.forename: Peter M
authors.initials: PM
authors.lastname: Scholz
authors.forename: Harvey R
authors.initials: HR
authors.lastname: Weiss
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D000242:Cyclic AMP / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D006152:Cyclic GMP / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D004334:Drug Administration Schedule; D004357:Drug Synergism; D006151:Guanosine / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects / Q000473:pathology; D006984:Hypertrophy / Q000139:chemically induced* / Q000201:enzymology; D007273:Injections, Intramuscular; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology; D032383:Myocytes, Cardiac / Q000737:chemistry / Q000187:drug effects / Q000201:enzymology; D009929:Organ Size / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011817:Rabbits; D013268:Stimulation, Chemical; D013974:Thyroxine / Q000008:administration & dosage / Q000009:adverse effects*; D013997:Time Factors; D005680:gamma-Aminobutyric Acid / Q000031:analogs & derivatives*
chemical_list: C473217:8-(4-chloro-phenylthio)-2'-O-methyladenosine-3'-5'-cyclic monophosphate; D010750:Phosphoproteins; D006151:Guanosine; D015124:8-Bromo Cyclic Adenosine Monophosphate; C035169:8-bromoguanosine; D005680:gamma-Aminobutyric Acid; D000242:Cyclic AMP; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP; D013974:Thyroxine; C008842:4-amino-3-phenylbutyric acid