Force mapping of Vascular Smooth Muscle Cells with Atomic Force Microscopy: influence of norepinephrine on local stiffness distribution

Mechanical properties of vascular smooth muscle cells (VSMCs) obtained from a rabbit thoracic aorta were studied using the force mapping technique available on an atomic force microscope (AFM). Correlation of higher stiffness structures with fibrous protrusions apparent in topographical images was evaluated and the influence of adding a contractile agent to the cells was investigated. Furthermore, parameter b and c were used as main indices of mechanical properties, being the rate of stiffness change and initial stiffness, respectively. VSMCs showed a stiffness at the highest point of the cell close to that of endothelial cells in the medial wall of aortic bifurcations, being about 1.2 nN/μm, but parameter b was much lower than in endothelial cells. Moreover, the forceindentation curves of the VSMCs showed a wider scattering pattern. Parameter c seemed to decrease after addition of norepinephrine (NE), while parameter b remained constant. Also, the distribution of both parameters appeared more homogenous. This may indicate a more deformable state and thus a lower stiffness to facilitate contraction, but an unequivocal conclusion could not be agreed upon, due also to the low number of samples. The results however, encourage the progress of experiments in this area to further elucidate this remarkable behaviour.