Combined phospholamban ablation and SERCA1a overexpression result in a new hyperdynamic cardiac state.
OBJECTIVE
Phospholamban ablation or ectopic expression of SERCA1a in the heart results in significant increases in cardiac contractile parameters. The aim of the present study was to determine whether a combination of these two genetic manipulations may lead to further augmentation of cardiac function.


METHODS
Transgenic mice with cardiac specific overexpression of SERCA1a were mated with phospholamban deficient mice to generate a model with SERCA1a overexpression in the phospholamban null background (SERCA1(OE)/PLB(KO)). The cardiac phenotype was characterized using quantitative immunoblotting, sarcoplasmic reticulum calcium uptake and single myocyte mechanics and calcium kinetics.


RESULTS
Quantitative immunoblotting revealed an increase of 1.8-fold in total SERCA level, while SERCA2 was decreased to 50% of wild types. Isolated myocytes indicated increases in the maximal rates of contraction by 195 and 125%, the maximal rates of relaxation by 200 and 124%, while the time for 80% decay of the Ca(2+)-transient was decreased to 43 and 75%, in SERCA1(OE)/PLB(KO) hearts, compared to SERCA1a overexpressors and phospholamban knockouts, respectively. These mechanical alterations reflected parallel alterations in V(max) and EC(50) for Ca(2+) of the sarcoplasmic reticulum Ca(2+) transport system. Furthermore, there were no significant cardiac histological or pathological alterations, and the myocyte contractile parameters remained enhanced, up to 12 months of age.


CONCLUSIONS
These findings suggest that a combination of SERCA1a overexpression and phospholamban ablation results in further enhancement of myocyte contractility over each individual alteration.
Zhao
Wen
W
Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267-0575, USA.
Frank
Konrad F
KF
Chu
Guoxiang
G
Gerst
Michael J
MJ
Schmidt
Albrecht G
AG
Ji
Yong
Y
Periasamy
Muthu
M
Kranias
Evangelia G
EG
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics*; D000252:Calcium-Transporting ATPases / Q000032:analysis / Q000235:genetics*; D048429:Cell Size; D017353:Gene Deletion; D015870:Gene Expression; D015151:Immunoblotting; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000099211:Phospholamban
D002118:Calcium; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000099211:Phospholamban; C506944:Atp2a1 protein, mouse; C506947:Atp2a2 protein, mouse