Abstract 16252: In vivo β1 Adrenergic Receptor Blockade Reverses an Oxidative Modification Inhibiting the Na+-K+ Pump of Cardiac Myocytes in Heart Failure
Identifying mechanisms for beneficial effect of β1 adrenergic receptor (AR) blockade in heart failure may be useful for developing new treatments. Since a raised Na+ concentration ([Na+]i) in myocytes and high myocardial oxidative stress are important for cellular mechanisms of heart failure we examined the hypotheses that heart failure increases an oxidative modification that inhibits the Na+-K+ pump and that β1 (AR) blockade reverses oxidative pump inhibition. This would enhance Na+ export. We induced a myocardial infarction in rabbits by ligating the circumflex coronary artery. Heart failure was identified by a decrease in left ventricular ejection fraction measured by echocardiography and by blood brain natriuretic peptide levels. Glutathionylation of the β1 Na+-K+ pump subunit, a reversible oxidative modification that inhibits pump activity, was identified by coimmuno-precipitation and immuno-blotting techniques of cardiac myocyte lysate. Electrogenic Na+-K+ pump current (Ip, arising from 3:2 Na+-K+ exchange and normalized for cell capacitance) was identified as the ouabain-sensitive membrane current of voltage clamped myocytes. Ip was significantly reduced in myocytes from 5 rabbits with heart failure compared with myocytes from 5 sham rabbits (0.17 ± 0.02 pA/pF vs. 0.33 ± 0.04 pA/pF) while β1 pump subunit glutathyonylation measured with either of two independent techniques was significantly increased by 1.3-3 fold. There was no significant difference in expression of α1/β1 Na+-K+ pump subunits measured in lysate of myocytes from heart failure and sham rabbits. Treatment of 5 heart failure rabbits with 25 mg metoprolol/day in drinking water for 7 days before sacrifice significantly increased Ip to 0.36 ± 0.06 pA/pF and decreased β1 pump subunit glutathyonylation ∼1.5-fold. Treatment of normal control rabbits with metoprolol also significantly increased Ip and decreased β1 pump subunit glutathyonylation suggesting a primary pharmacological effect of the metoprolol-induced changes rather than an non-specific effect secondary to an improvement of heart failure.
Conclusion: The mechanism for efficacy of β1 AR blockade in heart failure is likely to include reversal of Na+-K+ pump inhibition caused by β1 pump subunit glutathyonylation.
- © 2012 by American Heart Association, Inc.