Influences of increased expression of the Ca2+ ATPase of the sarcoplasmic reticulum by a transgenic approach on cardiac contractility.
Congestive heart failure is a significant clinical problem and leads to abnormalities in Ca2+ transients and to decreases in the level of the Ca2+ ATPase of the sarcoplasmic reticulum according to reports to some investigators. The Ca2+ ATPase of the sarcoplasmic reticulum (SERCA2) contributes in an important manner to diastolic Ca2+ lowering and relaxation of the heart. To determine the contractile alterations resulting from increased SERCA2 expression, we generated transgenic mice overexpressing a rat SERCA2 transgene. In these mice, SERCA2 mRNA was increased 2.6-fold, the relative synthesis rate of SERCA2 protein 1.8-fold, and SERCA2 protein levels 1.2-fold. Functional analysis of Ca2+ handling and contractile parameters in isolated cardiac myocytes indicated that the intracellular Ca2+ decline and myocyte relengthening were each accelerated by 22-23%. In addition, studies in isolated papillary muscles showed that the time to half-maximal post-rest potentiation was significantly shorter, hinting at an increased Ca2+ loading of the sarcoplasmic reticulum. Furthermore, in vivo cardiac functional studies demonstrated a significant accelerated contraction and relaxation in SERCA2 transgenic mice. We also cloned a SERCA2 transgene and mutants of the phospholamban gene into E1 deleted replication-deficient human adenovirus 5 viral vectors and infected cardiac myocytes. In the cardiac myocytes, endogenous SERCA2 levels were decreased by PMA treatment. Infection of such myocytes with a SERCA2 expressing adenovirus could reconstitute the Ca2+ transient, and augmented oxalate facilitated SERCA2 Ca2+ uptake. In addition, phospholamban mutants with changes of basic to acidic amino acids in the cytoplasmic domain increased SERCA2 activity by 30-35%. These findings, therefore, suggest that increased SERCA2 activity can be achieved by increasing SERCA2 levels or by expressing phospholamban mutants. Increased SERCA2 activity can lead to significant enhancements of Ca2+ transients and myocardial contractility.
Dillmann
W H
WH
Department of Medicine, University of California, San Diego 92093-0618, USA.
D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism*; D003971:Diastole; D006321:Heart / Q000502:physiology*; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D009200:Myocardial Contraction / Q000235:genetics / Q000502:physiology*; D051381:Rats; D012519:Sarcoplasmic Reticulum / Q000201:enzymology / Q000502:physiology*
D000252:Calcium-Transporting ATPases; D002118:Calcium