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 α1, α2 and α3 mRNA expression was determined by solution hybridization. No cross-reactivity occurred between the three probes. α1 mRNA was expressed at about 5 and 10 times higher (p<0.001) concentrations than α2 and α3 mRNA, respectively, and α2 mRNA higher (p<0.001) than α3. There were no differences between right and left ventricles and between donor hearts and patients with dilated cardiomyopathy. In conclusion, Na, K-ATPase α1 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 β subunit or posttransciptional modification of the catalytic subunits.
