The principal investigator is frequently confronted by both premature and full-term newborn infants whose cardiovascular systems respond differently than that of adults. During her fellowship training in pediatric cardiology, the applicant gained an appreciation of the extensive physiologic studies documenting developmental changes in myocardial function. However, despite the large number of studies concerning physiologic aspects of developmental changes in myocardial function, the biochemical basis for these changes is poorly defined. The biochemical regulatory controls responsible for maintaining the cardiovascular status of infants during transition from intrauterine to extrauterine existence are the major interest of the principal investigator; the cardiac sarcoplasmic reticulum (SR) is the focus of the current proposal. Since the contractile state of the heart depends on precise regulation of Ca2+ concentration by the SR, it seems likely that alterations in Ca2+ handling by the SR could at least partially explain developmental changes in myocardial function. Preliminary data have shown significant differences in Ca2+ handling in crude preparations of cardiac SR isolated from fetal and maternal sheep. However, recent studies have shown that cardiac SR is subspecialized and these crude SR preparations are quite heterogenous. The hypothesis of this proposal is that developmental changes in SR Ca2+ handling are related to alterations in function, composition and distribution of free and junctional SR. The crude cardiac SR fractions from fetal and maternal sheep will be separated by centrifugation methods into subpopulations of free and junctional SR vesicles. Functional studies will characterize and compare Ca2+ handling in the SR populations from fetal and maternal hearts. This will include measurement of Ca2+-ATPase activity, Ca2+ uptake, efflux, as well as dependence of these variables on phosphorylation and agents such as ryanodine and ruthenium red. Compositional studies will address both protein and lipid components. Protein studies will include quantitation of specific SR proteins by radioimmunoassay using Western blotting techniques.
