Reduced level of serine(16) phosphorylated phospholamban in the failing rat myocardium: a major contributor to reduced SERCA2 activity.
OBJECTIVE
Heart failure is associated with alterations in contractile parameters and accompanied by abnormalities in intracellular calcium homeostasis. Sarcoplasmic reticulum Ca(2+) ATPase (SERCA2) and phospholamban (PLB) are important in intracellular calcium cycling. The aim of the present study was to examine mechanisms causing reductions in SERCA2 activity in the failing heart.


METHODS
Myocardial infarction (MI) was induced in male Wistar rats, and animals with congestive heart failure were examined 6 weeks after the primary operation.


RESULTS
Serine(16) monomeric and pentameric phosphorylated PLB were significantly downregulated (50 and 55%, respectively), whereas threonine(17) phosphorylated PLB was unchanged in failing compared to sham hearts. Protein phosphatases 1 and 2A were significantly upregulated (26 and 42%, respectively) and phosphatase 2C significantly downregulated (29%), whereas the level of protein kinase A regulatory subunit II remained unchanged during heart failure. Increasing PLB phosphorylation by forskolin in isolated cardiomyocytes after inhibition of the Na(+)-Ca(2+) exchanger activity had significantly greater effect on SERCA2 activity in failing than in sham cells (49 and 20% faster transient decline, respectively). Decreasing PLB phosphorylation by the protein kinase A inhibitor H89 had significantly less effect on SERCA2 activity in failing compared to sham cardiomyocytes (20 and 75% slower transient decline, respectively).


CONCLUSIONS
The observed changes in SERCA2 activity after increasing and decreasing serine(16) PLB phosphorylation in cardiomyocytes from sham and failing hearts, suggest that the observed reduction in serine(16) PLB phosphorylation is one major factor determining the reduced SERCA2 activity in heart failure after MI.
Sande
Jørn B
JB
Institute for Experimental Medical Research, Ullevaal University Hospital, Kirkeveien 166, N-0407 Oslo, Norway. j.b.sande@ioks.uio.no
Sjaastad
Ivar
I
Hoen
Ingvild B
IB
Bøkenes
Janny
J
Tønnessen
Theis
T
Holt
Even
E
Lunde
Per K
PK
Christensen
Geir
G
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000032:analysis / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000032:analysis*; D000252:Calcium-Transporting ATPases / Q000032:analysis*; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006333:Heart Failure / Q000378:metabolism*; D006706:Homeostasis; D015151:Immunoblotting; D007424:Intracellular Fluid / Q000737:chemistry; D007545:Isoproterenol / Q000494:pharmacology; D007546:Isoquinolines / Q000494:pharmacology; D008297:Male; D009203:Myocardial Infarction / Q000378:metabolism*; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D013449:Sulfonamides; D000099211:Phospholamban
D000318:Adrenergic beta-Agonists; D002118:Calcium; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D005576:Colforsin; D017868:Cyclic AMP-Dependent Protein Kinases; D004791:Enzyme Inhibitors; D007545:Isoproterenol; D007546:Isoquinolines; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D013449:Sulfonamides; D000099211:Phospholamban; C506948:Atp2a2 protein, rat; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide