Table 2.
Key features used to characterize the human cardiomyocyte phenotype
| Features | Measured parameters | Human adult cardiomyocyte |
|---|---|---|
| Size and morphology |
Shape (rod, round) Size (μm) Cell capacitance (pF) |
Elongated Rod shaped ~65% mononucleated |
| Sarcomeres |
Alignment Organization (Z lines, H zone, I bands, A bands) Molecular composition (MYH7:MYH6, MYL2:MYL7, TNNI1:TNNI3) |
Organized and aligned MYH7 predominant isoform in the ventricle MYL7 predominant isoform in the atrium |
| Electrophysiological properties |
AP (APA, RMP, V max, APD) Ion current densities and gating properties (I Na, I CaL, I CaT, I to, I Kur, I Kr, I Ks, I K1, I K,Ach, I K,ATP, I f) |
Typical atrial, ventricular, pacemaker, and Purkinje AP shapes [238, 239] Distinct ion current densities and function in atrial, ventricular, pacemaker, and Purkinje cardiomyocytes [238, 239] |
| Ca2+ handling and contractile force |
Ca2+ transients Force of contraction Ca2+ sparks and Ca2+ waves |
Efficient Ca2+ transient induction by Ca2+ influx through L-type Ca2+ channels (Ca2+-induced Ca2+-release) [52] Force of contraction: 10–50 mN/mm2 (ventricular myocytes) [240] Positive force-frequency relationship (Bowditch phenomenon) [241] Low rate of spontaneous Ca2+ release |
| Response to β-adrenergic stimulation (cascade of events) |
Chronotropic effect Inotropic effect Lusitropic effect |
Positive chronotropic, inotropic and lusitropic effects |
| Mitochondrial function and metabolic profile |
Oxygen consumption Glycolysis and ATP measurements Mitochondrial membrane potential Mitochondrial [Ca2+] Mitochondrial [Na+] Redox state Intramitochondrial pH ROS generation |
Mitochondria occupies one-third of the total volume of CMs ATP production occurs mainly through oxidative metabolism (predominantly fatty acids) |
| Conduction velocity |
Conduction velocity maps Expression level of ion channels and gap junction proteins Localization, density, and composition of gap junction proteins |
Generation of the electrical signal through Na+ channels and propagation through gap junctions Localization of gap junction proteins at cell borders |