Patterning, prestress, and peeling dynamics of myocytes

As typical anchorage-dependent cells myocytes must balance contractility against adequate adhesion. Skeletal myotubes grown as isolated strips from myoblasts on micropatterned glass exhibited spontaneous peeling after one end of the myotube was mechanically detached. Such results indicate the development of a prestress in the cells. To assess this prestress and study the dynamic adhesion strength of single myocytes, the shear stress of fluid aspirated into a large-bore micropipette was then used to forcibly peel myotubes. The velocity at which cells peeled from the surface, V-peel, was measured as a continuously increasing function of the imposed tension, T-peel, which ranges from; 0 to 50 nN/mum. For each cell, peeling proved highly heterogeneous, with V-peel fluctuating between 0 mum/s (similar to80% of time) and similar to10 mum/s. Parallel studies of smooth muscle cells expressing GFP-paxillin also exhibited a discontinuous peeling in which focal adhesions fractured above sites of strong attachment (when pressure peeled using a small-bore pipette). The peeling approaches described here lend insight into the contractile-adhesion balance and can be used to study the real-time dynamics of stressed adhesions through both physical detection and the use of GFP markers; the methods should prove useful in comparing normal versus dystrophic muscle cells.