Sarcoplasmic reticulum Ca2+ ATPase and cell contraction in developing rabbit heart

The purpose of the present study was to determine whether age-related chang es in the expression and function of the cardiac isoform of the sarcoplasmi c reticulum Ca2+-ATPase (SERCA2a) play a role in SR Ca2+ release and cell c ontraction SERCA2a protein levels and subcellular localization were compare d between fetal, neonatal, juvenile and adult New Zealand While rabbits. St udies of SERCA function in isolated myocytes were performed ill situ by exa mining the rate of reloading of the SR Ca2+ stores following caffeine-induc ed depletion. We found that significant quantities of SERCA2a were present early in immature heart and that SERCA2a expression reached adult levels wi thin 15-30 days after birth. Furthermore, SERCA2a protein is present as a s eries of transverse striations within the cell as early as 1 day of age. In contrast to previous studies of SERCA in vitro, the SERCA protein function bl situ was found to be comparable between neonatal and adult myocytes in maintaining SR Ca2+ stores. These results indicate that the paucity of SR C a2+ release in immature ventricular cardiac myocytes is not the result of i mmaturity in SERCA2a expression. (C) 2000 Academic Press.