Related Experiment Videos
beta-Adrenergic regulation of cAMP and protein phosphorylation in phospholamban-knockout mouse hearts
1Department of Pharmacology, University of Cincinnati College of Medicine, Ohio 45267-0575, USA.
Abstract:
The stimulatory effects of beta-adrenergic agonists reflect increases in intracellular adenosine 3',5'-cyclic monophosphate (cAMP) levels and phosphorylation of key regulatory proteins in the heart. One of these phosphoproteins is phospholamban (PLB) in sarcoplasmic reticulum, and ablation of PLB is associated with attenuation of the contractile responses to beta-adrenergic stimulation in the mouse heart. To determine whether this attenuation of beta-stimulation is due to altered phosphorylation characteristics of the other key cardiac phosphoproteins and/or to compensatory responses occurring in the absence of PLB, PLB-knockout and wild-type hearts were perfused and their protein phosphorylation patterns examined. The beta-adrenergic receptor density, adenylyl cyclase activity, tissue cAMP levels, and the basal phosphoprotein pattern were similar between PLB-knockout and wild-type hearts. Isoproterenol perfusion resulted in similar increases in the tissue cAMP levels and the degree of phosphorylation of troponin I, C protein, and the 21-kDa microsomal protein in wild-type and PLB-knockout hearts. These findings indicate that the attenuation of isoproterenol-mediated increases in contractility of the PLB-knockout hearts is not due to alterations in the beta-adrenergic signal transduction pathway or the degree of phosphorylation of the key cardiac regulatory phosphoproteins in myofibrils and sarcolemma.
Insights
Phospholamban (PLB) deficiency in mouse hearts attenuates beta-adrenergic stimulation. However, PLB knockout hearts show normal signaling pathways and protein phosphorylation, suggesting other compensatory mechanisms are involved.
Area of Science:
- Cardiovascular Physiology
- Molecular Cardiology
- Cardiac Excitation-Contraction Coupling
Background:
- Beta-adrenergic agonists stimulate heart contractility via increased intracellular cyclic adenosine monophosphate (cAMP).
- Phospholamban (PLB) is a key sarcoplasmic reticulum protein regulated by phosphorylation, influencing cardiac contractility.
- PLB deficiency in mice is linked to reduced contractile responses to beta-adrenergic stimulation.
Purpose of the Study:
- To investigate if PLB absence alters phosphorylation of other cardiac proteins or triggers compensatory responses.
- To elucidate the mechanisms behind the attenuated beta-adrenergic response in PLB-knockout mouse hearts.
Main Methods:
- Isolated perfused hearts from PLB-knockout and wild-type mice were used.
- Protein phosphorylation patterns were examined following beta-adrenergic stimulation (isoproterenol).
- Key signaling components including beta-adrenergic receptor density, adenylyl cyclase activity, and cAMP levels were assessed.
Main Results:
- PLB-knockout and wild-type hearts exhibited similar beta-adrenergic receptor density, adenylyl cyclase activity, and basal cAMP levels.
- Isoproterenol perfusion induced comparable increases in cAMP levels and phosphorylation of troponin I, C protein, and a 21-kDa microsomal protein in both groups.
- The degree of phosphorylation of key cardiac regulatory proteins remained unaltered in PLB-knockout hearts.
Conclusions:
- The attenuated response to beta-adrenergic stimulation in PLB-knockout hearts is not caused by defects in the beta-adrenergic signal transduction pathway.
- Altered phosphorylation of major cardiac regulatory phosphoproteins in myofibrils and sarcolemma does not explain the observed phenomenon.
- Further research is needed to identify the compensatory mechanisms responsible for the blunted response in the absence of PLB.