Stress relaxation of contracted collagen gels: disruption of actin filament bundles, release of cell surface fibronectin, and down-regulation of DNA and protein synthesis.

Relaxation of stressed collagen gels provides a model system uniquely suited to studying the regulation of cell morphology and biosynthetic function by tissue organization. Stress relaxation results in rapid, synchronous changes in cell morphology without enzymatic or other drug treatments, and makes possible an analysis of the initial cellular events associated with changes in tissue organization. During the first hour after stress relaxation, we observed transient hypercontraction of collagen gels and loss of collagen fibril organization as stress in the system dissipated. Morphological changes in the fibroblasts included retraction of pseudopodia, collapse of cytoplasmic actin filament bundles, and loss of cell surface fibronectin. Accompanying these morphological changes, we observed marked decreases in DNA and protein synthesis, especially of fibronectin and type I procollagens. These results show that changes in tissue organization can exert rapid and profound effects on the morphology and biosynthetic function of cells within the tissue.