Figure 5.

Cardiomyocytes and fibroblasts balance contraction and matrix production during heart development. (A) Assumptions in matrix stiffness limiting fibroblast population α₁ (and hence, collagen expression), while encouraging myofibril organization in cardiomyocytes (and hence, myosin expression) are incorporated in a model where tension derived from each module inhibits degradation of the other. (B) Fibroblast crowding is modeled by a Hill function of collagen protein (and hence tension) (13) with n_f and k_f as the critical point and amplitude, respectively, of the collagen mRNA synthesis rate. (C) Experimentally measured changes in both collagen-1 (COL1) and cardiac myosin expression (circles) in a developing embryonic chick heart (30) can be recapitulated by the model (protein, lines; mRNA, dashed lines). To see this figure in color, go online.