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Na,K-ATPase receptor subunits alpha 1, alpha 2 and alpha 3 mRNA in dilated cardiomyopathy
C Sylvén1, E Jansson, P Sotonyi
1Karolinska Institute at Department of Medicine, Huddinge Hospital, Sweden.
Insights
Down-regulation of sodium-potassium adenosine triphosphatase (Na,K-ATPase) activity in heart failure does not stem from altered mRNA levels of its catalytic subunits. Predominant alpha 1 mRNA expression remains unchanged in dilated cardiomyopathy.
Area of Science:
- Cardiology
- Molecular Biology
- Biochemistry
Background:
- Sodium-potassium adenosine triphosphatase (Na,K-ATPase) receptor density is reduced in chronic heart failure patients with diminished ejection fraction.
- Previous research indicated a downregulation of Na,K-ATPase receptor density correlating with decreased ejection fraction.
Purpose of the Study:
- To investigate if the downregulation of Na,K-ATPase observed in heart failure occurs at the messenger RNA (mRNA) level.
- To quantify the expression of Na,K-ATPase catalytic subunit alpha 1, alpha 2, and alpha 3 mRNA in human myocardium.
Main Methods:
- Analysis of myocardial tissue from six donor hearts and six explanted hearts due to dilated cardiomyopathy (ejection fraction 23 +/- 5%).
- RNA extraction followed by quantitative solution hybridization to determine mRNA expression levels of Na,K-ATPase alpha 1, alpha 2, and alpha 3 subunits.
- Ensured probe specificity to avoid cross-reactivity between the three mRNA subunits.
Main Results:
- Sodium-potassium adenosine triphosphatase (Na,K-ATPase) alpha 1 mRNA was the most abundant subunit, significantly higher than alpha 2 and alpha 3 mRNA.
- No significant differences in Na,K-ATPase alpha subunit mRNA expression were found between right and left ventricles.
- Myocardial mRNA expression levels of Na,K-ATPase catalytic subunits did not differ between donor hearts and hearts from patients with dilated cardiomyopathy.
Conclusions:
- Sodium-potassium adenosine triphosphatase (Na,K-ATPase) alpha 1 mRNA is the predominant catalytic subunit expressed in the human heart.
- Reduced ejection fraction in dilated cardiomyopathy is not associated with altered mRNA expression of Na,K-ATPase catalytic subunits.
- The observed downregulation of Na,K-ATPase activity in heart failure may involve the beta subunit or posttranscriptional modifications of the catalytic subunits.
Abstract:
Na,K-ATPase receptor density has been shown to be down-regulated with decreasing ejection fraction in patients with chronic heart failure. It was the aim of the present study to determine whether down-regulation is detected also at the mRNA level. Six donor hearts and six explanted hearts due to dilated cardiomyopathy (ejection fraction 23 +/- 5%) were analyzed. RNA was extracted. Quantitative Na,K-ATPase receptor catalytic subunit alpha 1, alpha 2 and alpha 3 mRNA expression was determined by solution hybridization. No cross-reactivity occurred between the three probes. alpha 1 mRNA was expressed at about 5 and 10 times higher (p < 0.001) concentrations than alpha 2 and alpha 3 mRNA, respectively, and alpha 2 mRNA higher (p < 0.001) than alpha 3. There were no differences between right and left ventricles and between donor hearts and patients with dilated cardiomyopathy. In conclusion, Na,K-ATPase alpha 1 mRNA is the predominant subunit expressed in human myocardium. Depressed ejection fraction in dilated cardiomyopathy is not associated with changed mRNA subunit expression. Documented downregulation of Na,K-ATPase activity, therefore, may be associated with the structural and membrane-related beta subunit or posttranscriptional modification of the catalytic subunits.