Molecular and Cellular Characterization of Cardiac Tissue in Postnatal Development

Extrapolating pharmacological and surgical therapies from adult (AD) studies to infant (INF)
patients is problematic because the knowledge of cellular electrophysiology and molecular
biology of human INF heart cells is limited. The investigators have studied developmental
differences in rabbit ventricular cells and now extend these studies to atrial and
ventricular cells isolated from AD, young adult (YAD) or INF patients.

The study aims are as follows:

1. Developmental differences in transient outward current of atrial cells. Investigators
will extend their studies to isolated cells and tissue from YADs (age 14-20). In
addition, several other accessory beta-subunits have been found in cardiac myocytes and
may interact with Kv channels and regulate the function of these channels. The study
team will determine relative amounts of these putative regulators of human atrial Ito to
determine which correlate with developmental changes in Ito kinetics.

2. Developmental differences in amplitude and regulation of calcium current in atrial
cells. Investigators hypothesize that INF atrial cells have tonic inhibition of adenylyl
cyclase (and thus of ICa) mediated by inhibitory G proteins, possibly related to
constitutive activity of the adenosine A1 receptor, and that, compared to AD or YAD
cells, have greater sensitivity to inhibitors of phosphatases and phosphodiesterases,
and that developmental changes in basal ICa amplitude and beta-sympathetic modulation
correlate with inhibitory G protein levels, receptor numbers for M2 and A1 receptors,
and constitutive inhibitory activity.

3. Modulation of atrial cell calcium transients by changes in AP waveform and developmental
age. The study team will test the hypothesis that prolongation of the early
repolarization phase of the after potential (AP) increases Ca2+ entry and that YAD cells
have faster removal of Ca2+ from cytoplasm than INF cells and will determine if the Na-
Ca2+ exchange current (INCX) is greater in INF vs. AD or YAD cells.

4. Developmental differences in Ca current and transients and contractility in ventricular
cells. Investigators propose that INF cells and tissue have lower basal ICa, lower
potency for Isoproterenol stimulation, higher levels of Gialpha3 and A1 receptors,
greater inhibitory potency for adenosine, and tonic inhibition of ICa. We also propose
that the YAD cells have lower levels of NCX and lower INCX, higher levels of SERCA and
faster removal of Ca2+ from the cytoplasm. Previous animal studies have indicated
various developmental changes in cardiac cells. We will specifically study human
postnatal developmental changes in Ito, regulation of ICa and intracellular Ca2+
transients.

5. Structural, Functional and Metabolic Maturation of hPSC-CMs. Investigators propose that
combinations of 3D cardiac spheres with multiple environmental cues to improve
mitochondrial fatty acid oxidation (FAO or beta-oxidation) pathway will promote
functional and metabolic maturation of hPSC-CMs and generate a more clinically relevant
model. using tissue engineering combined with pharmacological agents to regulate signals
that are involved in FAO metabolism and appropriate growth factor and hormonal signaling
that mimic the microenvironment for the maturation of CMs.

Inclusion Criteria:

- Patients undergoing cardiopulmonary bypass surgery

Exclusion Criteria:

- Prior cardiac surgery

- History of atrial fibrillation or other atrial arrhythmias prior to operation