mice (The Jackson Laboratory, Bar Harbor, Maine) by a 2-step procedure as
previously described with modification (11 (link), 18 (link), 33 ). Briefly, in step 1, ventricular heart tissues
were minced to a size of 1 mm3 followed by digestion with 0.1%
collagenase IV and 1 U/mL Dispase in DMEM/F-12. The digested heart tissue was
seeded into 6 well plated coated with fibronectin/gelatin (0.5 mg fibronectin in
100 mL 0.1% gelatin). Cardiac explant cultures were maintained until small,
round, phase-blank cells migrated from adherent explants and proliferated on the
fibroblast layer. We then depleted hematopoietic cells using the mouse
hematopoietic lineage depletion cocktail kit (Stemcell Technologies) by magnetic
activated cell sorting (MACS) followed by enriching Sca-1 + cells with Sca-1
magnetic beads (Miltenyi Biotec Inc., Auburn, CA) as instructed by the
manufacturer’s protocol. The sorted Sca-1 cells were cultured in complete
medium (DMEM/F12 containing 10% fetal bovine serum (FBS), 200mmol/L L-Glutamine,
55nmol/L β-mercaptoethanol and 1% MEM non-essential amino acid).