Sarcoplasmic reticulum CA²⁺-atpase protein expression in developing rabbit heart

In adult heart, sarcoplasmic reticulum Ca²⁺-ATPase (SERCA2a) plays a crucial role in myocyte relaxation by transporting Ca²⁺ into the sarcoplasmic reticulum during diastole. However, little information is available regarding SERCA2a expression in immature mammalian myocardium. Accordingly, we have investigated SERCA2a protein levels in fetal (F, 28 day gestation), neonatal (1 day, 5 day), juvenile (15 day, 30 day) and adult (AD) rabbit ventricular myocardium using immunoblotting techniques. Sarcoplasmic reticulum membranes were isolated from homogenized tissues and protein concentrations were determined by Lowry assay with BSA as a standard. Western blot utilizing a monoclonal antibody recognized a single ∼110 kDa band representing SERCA2a. SERCA2a protein increased between 1 day and 30 day (in relative units, F= 1.1 ± 0.2; 1 day=1.0; 5 day=4.5 ± 1.5; 15 day=4.8 ± 1.4; 30 day= 6.3 ± 1.8; AD=4.9±0.6, n=3). These data indicate that SERCA2a protein is present during late fetal development and increases from birth to one month of age. Age-related changes in SERCA2a protein level may reflect the changing role of SERCA2a in excitation-contraction coupling during postnatal development.