Dynamic AFM elastography reveals phase dependent mechanical heterogeneity of beating cardiac myocytes

We developed a novel atomic force microscope (AFM) indentation technique for mapping spatiotemporal stiffness of spontaneously beating neonatal rat cardiac myocytes. Cells were indented at a rate close but unequal to their contractile frequency. Resultant apparent elastic modulus cycled at a predictable envelope frequency between a systolic value of 26.2 +/- 5.1 kPa and a diastolic value of 7.8 +/- 4.1 kPa. In cells probed along their axis, spatial heterogeneity of systolic stiffness correlated with the sarcomeric structure of underlying myofibrils. Treatment with blebbistatin eliminated contractile activity and resulted in a uniform modulus of 6.5 +/- 4.8 kPa. The technique provides a unique means of probing the mechanical effects of disease processes and pharmacological treatments on beating cardiomyocytes at the subcellular level, providing new insights relating myocardial structure and function.