Differential Response of Cardiomyocytes to Vectors and Rates of Cyclic Strain

Biomechanical forces play a dramatic role in cardiac muscle adaptation and disease. Relevant mechanical elements include tensile, compressive, and shear stress. The mechanism by which cells detect complex cyclic mechanical strain is poorly understood. Therefore the hypothesis is that the direction and rate of cyclic mechanical strain regulate protein phosphorylation and localization. The Flexcell stretch device administers cyclic strain of desired amplitude and frequency, which determines strain characteristics. We previously mimicked in vivo alignment of cardiocytes with microfabricated grooved architecture and here orient cultured neonatal rat myocytes to a uniaxial force vector either transverse or longitudinal to the cell axis. Focal adhesion kinase (FAK) is a membrane associating protein which has been shown to have a strain dependent increase in phosphorylation. Using western blot detection, we find strain rate dependence as well with a 50% increase in FAK phosphorylation over 0.5 to 2.0 Hz (p<0.05). The magnitude of the response is less at high cell density. Our initial results show anisotropic effects with a 25% higher FAK phosphorylation due to strain across the transverse axis compared with the long axis (n=2). This work suggests that myocytes discriminate between both the rate of rise and direction of force. Funded by HL 077995, HL 64956 and HL 62426.