Table 2.

Main characteristics of hiPSC-CMs and human adult CMs.

Characteristics	Parameters		hiPSC-CMs	Human Adult CMs	Assessment Methods
Morphology and Microstructure	Cell Shape		Round shape	Rod shape, anisotropic	Imaging Immunostaining to assess structural features
	Cell size	Length	5–10 μm (diameter)	150 μm
		Width		20 μm
		Height	5 μm	15 μm
		Volume	2000 μm3	40,000 μm3
	Length/width ratio		—	7:1
	Nucleation and ploidy		Mononucleated, diploidy	Binucleated (25%) and polyploidy
	Sarcomere		1.6 μm, disorganized	1.8 μm (contracted)-2.2 μm (relaxed), organized
	Enriched isoforms		α-MHC, ssTnI, MLC2A, N2BA, SMA	β-MHC, cTnI, MLC2V, N2B
	Other microstructures		Lack T-tubules and M-band; poor SR, mitochondria; circumferential IDs	Developed and abundant microstructures; polarized IDs
Electrophysiology	Beating		Beating spontaneously or stimulated by a 0.08–4 mN/mm2 force	Beating only when stimulated by a 40–80 mN/mm2 force	Patch clamp and MEAs for ion channels and AP currents Video-optical recording, atomic force microscopy (AFM). and muscle thin films (MTFs) for contractile force measurements (Frank–Starling relationship)
	Membrane capacitance		~20 pF	~190 pF
	Conduction velocity		10–20 cm/s	60 cm/s
	Upstroke velocity		10–50 V/s	150–350 V/s
	Action potential		−60 mV (like nodal)	−90 mV
	Specific currents		I Kf	I K1
Calcium Handling	ECC		Slow	Fast	Calcium imaging using fluorescent calcium indicators
	Ion channels		NCX	LTCC-β2 (20-fold higher), RyRs (1000 folds higher), calsequestrin, SERCA
Metabolism	Mitochondria		Round shape with poor cristae	Oval shape with developed cristae; active fission and fusion	Mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR) for metabolic flux assays Oxygen consumption and extracellular acidification rate to access mitochondria respiration Imaging and fluorescent staining for mitochondrial membrane potential (MMP)
	Abundance (% to cell volume)		<5%	~30%
	Location		Perinuclear space	Between myofibrils and under sarcolemma
	Metabolic substrate		Glucose (85%), fatty acid (15%)	Fatty acid (80%), glucose (20%)
	ATP source		Anaerobic glycolysis	FAO
Gene Expression	Upregulated genes		Cell-cycle genes: CDK Automaticity genes: HCN4, KCNJ2 Fetal/natal isoform genes Glycolysis-related genes	Cell-cycle arrest genes: CDKI Overall upregulation of structure organization and function development genes	Imaging Flow cytometry to access cell cycle Fluorescent staining

AFM, atomic force microscopy; AP, action potential; cTnI, cardiac muscle troponin I; ECC, excitation–contraction coupling; FAO, fatty-acid oxidation; ID, intercalated disc; LTCC-β2: L-type calcium channel β subunit; MEA, microelectrode array; MLC2A, myosin regulatory light chain 2 atrial isoform; MLC2V, myosin regulatory light chain 2 ventricular isoform; MMP, mitochondrial membrane potential; MS, mass spectrometry; MTF, muscle thin film; N2B; titin isoform type containing only N2B elements; N2BA, titin isoform type containing both N2A and N2B elements; NCX, Na⁺–Ca²⁺ exchanger; NMR, nuclear magnetic resonance spectroscopy; RyR2, ryanodine receptor 2; SERCA, sarco/endoplasmic reticulum Ca²⁺ ATPase; SMA, smooth muscle actin; SR, sarcoplasmic reticulum; ssTnI, slow skeletal muscle troponin I; α-MHC, myosin heavy chain α-isoform; β-MHC, myosin heavy chain β-isoform; pF, picofarad.