Optical Method to Quantify Mechanical Contraction and Calcium Transients of Human Induced Pluripotent Stem Cell Derived Cardiomyocytes

Differentiation of induced pluripotent stem cells into cardiomyocytes (iPS-CM) holds promise for myocardial regeneration therapies, drug discovery, and models of cardiac disease. Currently, no method exists to easily and... [ view full abstract ]

Differentiation of induced pluripotent stem cells into cardiomyocytes (iPS-CM) holds promise for myocardial regeneration therapies, drug discovery, and models of cardiac disease. Currently, no method exists to easily and reproducibly measure changes in mechanical contraction and calcium transients over long-term culture. Here, we describe a method to measure iPS-CM contractility with high spatial and temporal resolution, while concurrently capturing calcium transients. The image capture system rapidly alternates (>140fps) between bright (mechanical) and fluorescent (calcium transients) fields of contracting cells. A speckle tracking algorithm is applied to the brightfield images to determine contractile strain and beat frequency. By concurrently recording the calcium transients, information about the temporal relationship between calcium transients and mechanical components leading to contraction of cardiomyocytes can be obtained. Using this technique, contractile behavior of iPS-CM seeded on collagen IV (10µg/mL; n=6) coated coverslips was analyzed over 21 days. Cells exhibited a contractile strain on day 7 of 4.2±0.57%, which significantly decreased to 2.6±0.24% strain on day 21 (p<0.05). iPS-CMs showed increased beating frequency over time; cells exhibited a significantly higher (p<0.001) beat frequency on day 21 (1.52±0.09Hz) compared to day 7 (1.06±0.09Hz). To confirm loss of mechanical contraction with no change in calcium transients, Cytochalasin-D (10µM), an inhibitor of actin polymerization, was added resulting in inhibition of mechanical contraction with no effects on calcium transients. The technique described above can be applied without altering the culture platform allowing for determination of iPS-CM behavior over weeks in culture providing benefits for drug discovery and myocardial regeneration strategies.