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Interaction between cyclic GMP protein kinase and cyclic AMP may be diminished in stunned cardiac myocytes
1Heart and Brain Circulation Laboratory, University of Medicine and Dentistry of New Jersey (UMDNJ), Robert Wood Johnson Medical School, Piscataway, NJ 08854-5635, USA.
Abstract:
We tested the hypothesis that the importance of the negative functional effects of the cyclic GMP protein kinase would be reduced in stunned (simulated ischemia/reperfusion) cardiac myocytes. Ventricular cardiac myocytes were isolated from New Zealand white rabbits (N=7). Myocytes were studied at baseline and after simulated ischemia (15 min of 95% N(2)-5% CO(2) at 37 degrees C) followed by simulated reperfusion (reoxygenation). Cell shortening was studied with a video edge detector; O(2) consumption was measured using O(2) electrodes. Protein phosphorylation was measured autoradiographically after gel electrophoresis. Functional and metabolic data were acquired after: (1) 8-(4-chlorophenylthio)guanosine-3',5'-monophosphate (PCPT, cGMP protein kinase agonist) 10(-7) or 10(-5) M; (2) 8-Br-cAMP 10(-5) M followed by PCPT 10(-7) or 10(-5) M; (3) beta-phenyl-1, N(2)-etheno-8-bromoguanosine-3',5'-monophosphorothioate, SP-isomer (SP, cGMP protein kinase agonist) 10(-7) or 10(-5) M; (2) 8-Br-cAMP 10(-5) M followed by SP 10(-7) or 10(-5) M. At baseline, percent of shortening (Pcs) and maximal rate of shortening (Rs) were significantly lower in the stunned myocytes (Pcs: 5.0+/-0.2% control vs. 3.8+/-0.3 stunned; Rs: 64.8+/-5.9 microm/s control vs. 46.9+/-4.8 stunned). In both groups, PCPT and SP dose-dependently decreased Pcs and Rs. The effects were slightly, but not significantly, less in stunned myocytes. 8-Br-cyclic AMP significantly increased function in control, but not stunned myocytes (Pcs, 4.5+/-0.5 to 6.2+/-0.8 control vs. 3.1+/-0.2 to 3.6+/-0.2 stunned). The negative functional effects of PCPT and SP were diminished after 8-Br-cyclic AMP in control (from -39% to-29%) and diminished significantly more in the stunned myocytes (-19%). PCPT and cyclic AMP phosphorylated similar protein bands. In stunned myocytes, three (22, 31 and 53 kDa) bands were enhanced less by PCPT.
Insights
This study investigated how cyclic GMP protein kinase affects stunned cardiac cells. Results show its negative effects are reduced in stunned cells, especially after cyclic AMP treatment, suggesting a protective role.
Area of Science:
- Cardiovascular Physiology
- Cellular Biology
- Biochemistry
Background:
- Cardiac stunning, resulting from simulated ischemia/reperfusion, impairs myocyte function.
- Cyclic GMP protein kinase plays a role in cardiac cell function and response to stress.
Purpose of the Study:
- To test if the negative functional effects of cyclic GMP protein kinase are reduced in stunned cardiac myocytes.
- To investigate the interaction between cyclic AMP and cyclic GMP pathways in stunned myocytes.
Main Methods:
- Isolated rabbit ventricular cardiac myocytes were subjected to simulated ischemia/reperfusion.
- Cell shortening, oxygen consumption, and protein phosphorylation were measured.
- Myocytes were treated with cyclic GMP protein kinase agonists (PCPT, SP) and cyclic AMP (8-Br-cAMP).
Main Results:
- Stunned myocytes exhibited significantly reduced cell shortening compared to control myocytes.
- Both PCPT and SP dose-dependently decreased cell shortening in control and stunned myocytes, with a trend towards less effect in stunned cells.
- 8-Br-cyclic AMP improved function in control but not stunned myocytes; it diminished the negative effects of PCPT/SP more significantly in stunned myocytes.
Conclusions:
- The negative functional impact of cyclic GMP protein kinase agonists is reduced in stunned cardiac myocytes.
- The interplay between cyclic AMP and cyclic GMP pathways is altered in stunned myocytes, potentially offering a protective mechanism.
- Specific protein phosphorylation patterns by cyclic GMP protein kinase are less pronounced in stunned myocytes.