This research is funded by the North Shore Heart Research Foundation
On this page:
Overview
Benefits of this research
Study 1
Study 2
Study 3
Study 4
Study 5
Publications and presentations
Overview
Our researchers have identified a novel mechanism of regulation of the sodium potassium pump in cardiac and vascular cells. They are currently working on several parallel projects to develop this understanding.
This knowledge has important implications for identifying treatment targets for heart failure, hypertension and other cardiovascular diseases.
This project is testing the potential of a selective analogue of ANP (atrial naturiuretic peptide) as a powerful drug for treating heart failure. Preliminary results are promising. We have demonstrated the beneficial effect of this analogue on heart function. Final results are expected in 2010.
The laboratory is recognised internationally for its expertise in cellular electrophysiology, in particular using whole cell patch clamp techniques for measuring sodium pump activity in isolated cardiac myocytes.
Benefits of this research
Despite the well-described role of reactive oxygen species and oxidation in a number of disease states including heart failure, trials of treatment with general antioxidants have been unsuccessful in modifying their clinical course.
Our discovery that hormones upregulated in heart failure activate an intracellular enzyme that produces reactive oxygen species, resulting in direct oxidative modification and inhibition of the Na+-K+ pump, provides new insight into the pathogenesis of heart failure. This may offer potential new therapeutic targets.
Study 1
Title: Haemodynamic effects of ANP and cANP on an ovine rapid paced heart failure model
Investigators: Professor Helge Rasmussen, Professor Stephen Hunyor
Funded since 2007
Report
We have found that atrial natriuretic peptide (ANP) induces stimulation of Na+-K+ pump activity in rabbit ventricular myocytes, an effect that is lost at higher concentrations. This biphasic action may explain why increasing the tissue levels of natriuretic peptides (e.g. with neutral endopeptidase inhibitors to block breakdown, or direct ANP infusion) does not improve or may even worsen clinical outcomes in heart failure.
This project examines whether specific natriuretic peptide receptor C (NPR-C) stimulation eliminates the biphasic ANP effect, leading to improved haemodynamics in a sheep heart-failure model.
Recent data show definite effects of both ANP and cANP on cardiac contractility, assessed by pressure-volume loops in sheep, with cANP possibly showing slightly better contractility at higher concentrations than ANP.
Further sheep experiments will be required to confirm this observation and its potential clinical significance.
Study 2
Title: Reversible oxidative modification of the sodium pump - role in hormonal regulation of vascular tone
Investigators: Dr Gemma Figtree and Professor Helge Rasmussen
Funded since January 2008
Overview
We have recently identified a novel signalling pathway by which reactive oxygen species superoxide and peroxynitrite inhibit the Na+-K+ pump in cardiac myocytes. Such a pathway may also be important in vascular smooth muscle cells, with important implications for our understanding of hypertension and atherosclerosis. This study aims to examine for oxidative modification of Na+-K+ pump subunits, and any associated functional effect in vascular smooth muscle cells and blood vessels.
Understanding the contribution of Na+-K+ pump activity and its regulation to vasomotor tone has important implications for hypertension and vascular disease. Our recent identification of the molecular mechanism by which hormones and reactive oxygen species inhibit the Na+-K+ pump may provide a target for the development of novel therapies for these disorders.
Report
The Na+/K+ pump maintains the trans-membrane gradient for Na+ and K+. This gradient is the primary determinant of Na+-Ca2+ exchange, thus influencing the contractile function of cardiac myocytes, as well as vascular smooth muscle cells.
Our laboratory has extensive experience in characterising the complex pathways involved in Na+-K+ pump regulation in the heart. This work has resulted in identifying a novel role for oxidant species superoxide and peroxynitrite in the hormonal regulation of the Na+-K+ pump in the heart. We have discovered that Na+-K+ pump inhibition occurs by the reversible oxidative modification of a specific cysteine residue of the b1 subunit of the pump.
This project examines for similar oxidative modification of the Na+-K+ pump in vascular smooth muscle cells where it may play a key role in the regulation of blood vessel tone.
We have used western blotting techniques to demonstrate b1 subunit expression in human cultured vascular smooth muscle cells, as well as rabbit aorta. We are now examining for reversible oxidative modification of the b1 subunit in these cell types.
In parallel with these experiments, we have established organ bath techniques to determine the contribution of Na+-K+ pump inhibition and stimulation to vasoconstriction and vasodilatation in response to various hormones. Specifically, by removing the potassium from the bath solution we can effectively disable the Na+-K+ pump. This substantially reduces the classic vasodilatation in response to nitrate donors, suggesting that Na+-K+ pump stimulation by NO is a major mechanism involved.
In contrast, we have identified a component of Angiotensin II- induced vasoconstriction that is dependent on Na+-K+ pump inhibition. Understanding the response of the vascular Na+-K+ pump to physiological and pathological exposure to reactive oxygen species may aid in the development of therapies targeting hypertension and atherosclerosis.
Study 3
Title: Rapid and reversible oxidative modification of the cardiac Na+-K+ pump and its role in hormonal regulation
Investigators: Dr Gemma Figtree and Professor Helge Rasmussen
Funded since January 2009
Overview
Heart failure is a debilitating condition characterised by a decreased heart pump function. Raised Na+ levels and increased oxidative stress in cardiac cells are important in its causation. The membrane Na+-K+ pump is effectively the sole exporter of Na+ from the cell, and its regulation therefore has important implications.
We have recently identified reactive oxygen species as key in the regulation of the Na+-K+ pump. This project examines the molecular mechanism by which this regulation occurs, as well as the role of reactive oxygen species in hormonal control of pump activity, both under physiological conditions and in disease states.
Report
The membrane Na+-K+ pump is the key determinant of intracellular Na+ in the cardiac myocyte. This is of particular importance in heart failure, a condition in which raised levels of intracellular Na+ contribute to both impaired contractility as well as arrhythmias.
Data from patch clamp experiments in our laboratory suggest a role for reactive oxygen species in the signalling pathways regulating the Na+-K+ pump. For example, Angiotensin II, a hormone that is severely dysregulated in heart failure, inhibits the Na+-K+ pump in a manner that depends on the production of superoxide and peroxynitrite. This led us to examine the molecular mechanism through which this may occur.
First we identified oxidative modification of a specific cysteine residue of the b1 subunit of the Na+-K+ pump. This increased with exposure to chemical oxidants, and resulted in decreased association of the b1 subunit with the
catalytic a1 subunit, and subsequent inhibition of pump activity. Collaborators from the University of Laussanne mutated this cysteine residue, and found that this abolished oxidant-induced inhibition of the Na+K+ pump.
This work was recently published in Circulation Research, one of the leading journals in basic cardiovascular research, and has provided a novel mechanism for understanding Na+K+ pump regulation.
Having established the molecular mechanism by which reactive oxygen species inhibit the activity of the cardiac Na+-K+ pump, we examined for the role that this might play in its regulation by hormones, particularly Angiotensin II.
We found and have recently published that Angiotensin II activates the enzyme NADPH oxidase to increase local concentrations of superoxide and reactive oxygen species. This results in receptor-coupled inhibition of the Na+-K+ pump through oxidative modification of the b1 subunit. Of interest, adrenergic signalling, also upregulated in patients with heart failure, activates this pathway, and inhibits the Na+-K+ pump. This data has significant implications for our understanding of heart failure, and for our identification of targets for novel therapies.
Study 4
Title: Molecular mechanism of insulin induced Na-K pump stimulation in cardiac myocytes
Investigators: Dr Chia-Chi Liu, Dr Gemma Figtree and Professor Helge Rasmussen
Funded since January 2010
The sodium-potassium (Na-K) pump is regarded as a significantly important molecule in cell biology. However to date, little is known about how the body controls and regulates the Na-K pump, in health or disease.
Oxidative stress is well known in the scientific community as a destructive process involved in a number of disease processes such as cardiovascular disease. In addition, oxidative stress is needed to regulate the Na-K pump to perform its normal function.
Dr Chia-Chi Liu is studying the effects of insulin on altering the Na-K pump function. In investigative trials, it was discovered that insulin could be used as a form of protection against harmful levels of oxidative stress.
The objective in furthering this research is to evaluate the clinical applications of this finding.
This research presents great therapeutic potential as knowledge about these mechanisms is likely to lead to drug therapies for various forms of heart disease, benefiting many Australians.
The first research report for this project will be available at the end of 2010.
Study 5
Title: The effect of diabetes and infarct-induced cardiomyopathy on function of the cardiac Na-K pump, oxidative modification of its beta-1 subunit and interaction of alpha 1/beta 1 subunits
Scholarship recipient: Dr Kevyan Karimi Galoughahi
Dr Kevyan Karimi Galougahi is investigating the changes in the Na-K pump in heart muscle in diabetes and heart failure.
After characterising such changes, it will be possible to examine the effect of drugs that specifically modify the function of the pump.
This research could potentially explore novel ways of cardio-protection and treatment, leading to a reduction in deaths and disability associated with diabetes and heart failure.
The first research report for this project will be available at the end of 2010.
Publications and presentations
Figtree, G.A., Liu, C.C., Bibert, S., Hamilton, E.J., Garcia, A., White, C.N., Chia, K.K., Cornelius, F., Geering, K., Rasmussen, H.H. ‘Reversible oxidative modification: a key mechanism of Na+-K+ pump regulation. ‘ Circulation Research 105, no. 2 (Jul 17 2009): 185-93.
Rasmussen, H.H., Figtree, G.A., Krum, H., Bundgaard H. 'The use of beta3-adrenergic receptor agonists in the treatment of heart failure.' Current Opinion in Investigational Drugs 10, no. 2 (Sept 2009): 955-62.
White, C.N, Figtree, G.A., Liu, C.C., Garcia, A., Hamilton, E.J., Chia, K.K., Rasmussen, H.H. ‘Angiotensin II inhibits the Na+-K+ pump via PKC-dependent activation of NADPH oxidase.' American Journal of Physiology - Cell Physiology 296, no. 4 (Apr 2009): C693-700.
Seminar, University of Lausanne, Switzerland, June 2009
Rasmussen, Helge. ‘Receptor-coupled oxidative signalling and regulation of the Na-K pump by reversible glutathionylation.'
European Society of Cardiology (ESC) Working Group on Cardiovascular Pharmacology and Drug Therapy. Copenhagen, June 2009
Rasmussen, Helge. ‘Hypertrophy and failure - the crucial role of the Na-pump.'
European Society of Cardiology (ESC) Working Group on Cardiovascular Pharmacology and Drug Therapy, Copenhagen, June 2009
Rasmussen, Helge. ‘Hypertrophy and failure - the crucial role of the Na-pump.
Third Biennial MyoNaK Conference, Palm Cove, Australia, August 2009
Figtree, Gemma. ‘Reversible oxidative modification: a key mechanism of Na-K pump regulation.'
Rasmussen, Helge. ‘PKA inhibits the cardiac Na-K pump via PKC- and NADPH oxidase dependent glutathionylation'.
International FXYD Symposium, Philadelphia, October 2009
Figtree, Gemma. ‘Regulation of the Na-K pump by oxidative modification of FXYD proteins as studied in Xenopus oocytes.'
Rasmussen, Helge. ‘Role of oxidative modification of FXYD proteins in the regulation of the Na-K pump. Studies in cardiac myocytes.'
