THE SUBCELLULAR BASIS FOR THE PERINATAL MATURATION OF THE CARDIOCYTE

In the experimental animal, the transition from tetus to newborn to adult has long been associated with an improvement in systolic and diastolic cardiac function. Recent studies using noninvasive methods have demonstrated a similar perinatal improvement in ventricular function in the human. These perinatal changes in cardiac function have been correlated with subcellular changes in expression of sarcoplasmic reticulum Ca2+ release channel and Ca2+ ATPase proteins (the primary regulators of phasic Ca2+ cycling in the mature heart), as well as with isoform switching among the myofibrillar proteins. The reduced sarcoplasmic reticulum-dependent regulation strongly supports the concept that during perinatal maturation, systolic and diastolic cardiac function are more dependent on transsarcolemmal Ca2+ flux.