Ventricular remodelling associated with cardiac disease (e.g. hypertrophy) involves structural (and molecular and cellular) changes at the cardiomyocyte level that may alter stiffness (and therefore function) of the cardiomyocyte and consequently the cardiac pump. Atomic Force Microscopy (AFM) with its nanoindentation function (using a nano-sharp blunt cone) has been used in recent years to determine the viscoelastic properties of cardiomyocytes. However, it has been suggested that this involves exerting significant physical force on cells which may influence their cytoskeleton and therefore may not be a true reflection of their physical properties. To reduce the physical force we decided to use spheres attached to the cantilever tip to measure the apparent elastic moduli of freshly isolated non-perfused cardiomyocytes. In this study we report preliminary data showing heterogeneous distribution of elasticity in grids of 8x8 micron recorded with a 1 micron sphere tipped cantilever.
Ventricular cardiomyocytes were isolated from mice heart using a standard enzymatic digestion technique of Langendorff perfused heart. Quiescent cardiomyocytes were mapped by recording an array of 16 by 16 force curves over a grid of 8 micron (along the length of cell) by 8 micron (across width of cell). Youngs Modulus was calculated from each of the force curves thereby producing a force or elasticity map of the cell surface.
Our preliminary data show that the surface of cardiomyocytes is heterogeneous in elastic terms which may reflect the topography of the cardiomyocyte. The sphere size is critical in determining surface elasticity as large size spheres would span several sarcomeres. This approach that utilises minimum exerted force on myocytes can then be used to determine the physical properties of cardiomyocytes isolated from diseased heart. Additionally, this technique may ultimately aid development of drugs that influence membrane structure and can be used to provide evidence for recovery of physical properties following interventions to salvage/regenerate the myocardium.