Related Experiment Videos
Endothelin-1 does not phosphorylate phospholamban and troponin I in intact beating rat hearts
S Gando1, J Nishihira, Y Hattori
1Department of Pharmacology, Hokkaido University School of Medicine Sapporo, Japan.
Insights
Endothelin-1 does not increase cardiac regulatory protein phosphorylation, unlike isoprenaline. This suggests protein phosphorylation is not the mechanism behind endothelin-1's positive inotropic effect in the heart.
Area of Science:
- Cardiology
- Molecular Biology
- Biochemistry
Background:
- Endothelin-1 is known to induce a positive inotropic effect in the heart.
- The precise molecular mechanisms underlying this effect are not fully understood.
- Protein phosphorylation plays a crucial role in regulating cardiac contractility.
Purpose of the Study:
- To investigate the role of cardiac regulatory protein phosphorylation in mediating the positive inotropic effect of endothelin-1.
- To compare the effects of endothelin-1 on protein phosphorylation with those of known inotropic agents like isoprenaline.
Main Methods:
- Utilized perfused beating rat hearts labeled with 32Pi.
- Administered endothelin-1, isoprenaline, and phorbol-12,13-dibutyrate (PDB) to assess their impact on protein phosphorylation.
- Quantified the phosphorylation levels of sarcoplasmic reticulum and myofibrillar proteins, specifically phospholamban and troponin I.
Main Results:
- Isoprenaline significantly increased the phosphorylation of phospholamban (4.4-fold) and troponin I (10.4-fold).
- Endothelin-1 and PDB did not induce significant changes in the phosphorylation state of these key cardiac regulatory proteins.
- These findings indicate a dissociation between endothelin-1's inotropic effect and major protein phosphorylation events.
Conclusions:
- Phosphorylation of major cardiac regulatory proteins, such as phospholamban and troponin I, is not the mechanism responsible for the positive inotropic action of endothelin-1.
- The positive inotropic effect of endothelin-1 likely involves alternative signaling pathways independent of these specific phosphorylation events.
Abstract:
To determine a role of phosphorylation of specific cardiac regulatory proteins in the positive inotropic effect of endothelin-1, we examined phosphorylation of sarcoplasmic reticulum and myofibrillar proteins in perfused beating rat hearts treated with endothelin-1. In parallel experiments, the effects of isoprenaline and phorbol-12,13-dibutyrate (PDB) on protein phosphorylation were also tested. In 32Pi-labeled hearts, perfusion with isoprenaline (100 nM) caused 4.4- and 10.4-fold increases in the degree of phosphorylation of phospholamban in sarcoplasmic reticulum and of troponin I in myofibrils, respectively. In contrast, neither endothelin-1 (100 nM) nor PDB (1 microM) significantly changed the phosphorylation state of these proteins. These findings provide evidence that phosphorylation of major cardiac regulatory proteins is not responsible for the positive inotropic action of endothelin-1.