Abstract 16287: Selective[[Unable to Display Character: ]] β3 [[Unable to Display Character: ]]Adrenergic Agonism Protects Against Oxidative Inhibition of Cardiac Na+-K+ Pump in Type 2 Diabetes
Background and hypothesis:[[Unable to Display Character: ]]β3 adrenergic receptor (AR) agonists stimulate the Νa+-K+ pump in isolated cardiac myocytes by reversing glutathionylation of its β[[Unable to Display Character: ]] subunit, an oxidative modification that inhibits pump activity. Since diabetes is associated with myocardial oxidative stress and inhibition of the Na+-K+ pump, we examined if the selective β3 AR agonist CL 316,243 (CL) alters oxidative inhibition of Na+-K+ pump in a novel model of type 2 diabetes. This has therapeutic implications for diabetic cardiomyopathy because of the known adverse effects of myocyte Na+ overload in failing heart.
Methods and results: Infusion of the insulin receptor peptide antagonist S961 via osmotic minipumps (12 μg/kg/hr) induced hyperglycemia and hyperinsulinemia in rabbits (n=10) and increased plasma lipid peroxidation. It also activated sources of O2.- in cardiac myocytes isolated from diabetic rabbits as indicated by an increase in co-immunoprecipitation (co-ip) of the cytosolic p47phox with membranous p22phox subunits of NADPH oxidase and by an increase in glutathionylation of endothelial nitric oxide synthase (eNOS) (58±6%) known to uncouple eNOS to generate O2.- rather than NO. Diabetes reduced co-ip of β[[Unable to Display Character: ]] Na+-K+ pump subunit with glutaredoxin 1 (Grx1) that selectively reverses glutathionylation of proteins. Consistent with the changes in O2.- sources and reduced Grx1/β[[Unable to Display Character: ]] subunit co-ip, glutathionylation of the β[[Unable to Display Character: ]] subunit was increased (52±9%) and electrogenic Na+-K+ pump current measured in voltage clamped myocytes was reduced (0.26±0.04 vs. 0.44±0.04 pA/pF). Co-administration of CL (40 μg/kg/hr) with S961 for the last 3 days of study had no effect on glucose or insulin levels but reduced lipid peroxidation. It also reduced p47phox/p22phox co-ip, reduced glutathionylation of eNOS (51±1%) and β[[Unable to Display Character: ]] Na+-K+ pump subunit (74±13%), increased Grx1/β[[Unable to Display Character: ]] Na+-K+ pump subunit co-ip and increased Na+-K+ pump current (0.6±0.1 vs. 0.26±0.04 pA/pF).
Conclusions: S961 diabetes induced molecular remodeling in an oxidative pathway that is determinant of the functionally important oxidative modification of the sarcolemmal Na+-K+ pump. Reversal of these changes by β3 AR stimulation suggests that β3 AR agonists may have cardiovascular protective effects in diabetes.
- © 2012 by American Heart Association, Inc.