Muscle cell peeling from micropatterned collagen: direct probing of focal and molecular properties of matrix adhesion

To quantitatively elucidate attributes of myocyte-matrix adhesion, muscle c ells were controllably peeled from narrow strips of collagen-coated glass. Initial growth of primary quail myoblasts on collagen strips was followed b y cell alignment, elongation and end-on fusion between neighbors. This geom etric influence on differentiation minimized lateral cell contact and cell branching, enabling detailed study of myocyte-matrix adhesion. A micropipet te was used to pull back one end of a quasi-cylindrical cell while observin g in detail the non-equilibrium detachment process, Peeling velocities fluc tuated as focal roughness, mu m in scale, was encountered along the detachm ent front. Nonetheless, mean peeling velocity (mu m/second) generally incre ased with detachment force (nN), consistent with forced disruption of adhes ion bonds. Immunofluorescence of beta 1-integrins correlated with the focal roughness and appeared to be clustered in axially extended focal contacts. In addition, the peeling forces and rates were found to be moderately well described by a dynamical peeling model for receptor-based adhesion (Dembo, M., Torney, D. C., Saxman, K. and Hammer, D. (1988), Proc. R. Sec. Lend. B 234, 55-83), Estimates were thereby obtained for the spontaneous, molecular off-rate (k(off)(o), less than or similar to 10/seconds) and the receptor complex stiffness (kappa, approx. 10(-5)-10(-6) N/m) of adherent myocytes, Interestingly, the local stiffness is within the range of flexible proteins of the spectrin superfamily, The overall approach lends itself to elucidat ing the developing function of other structural and adhesive components of cells, particularly skeletal muscle cells with specialized components, such as the spectrin-homolog dystrophin and its membrane-linked receptor dystro glycan.