Differences in the mechanism for high‐ versus moderate‐density fibroblast‐populated collagen lattice contraction

The free‐floating fibroblast‐populated collagen lattice (FPCL) model introduced by Bell contains 0.5 × 10 5 cell/ml and here is defined as a moderate‐density FPCL (MD‐FPCL). One modification of the model is to increase the cell density by a factor of 10, where 5 × 10 5 cells/ml defines a high‐density FPCL (HD‐FPCL). The initial detection of HD‐FPCL contraction is 2 h, whereas MD‐FPCL is later, 6 h. A contracted HD‐FPCL has a doughnut‐like appearance, due to the high density of cells accumulating at the periphery. A contracted MD‐FPCL is a flattened disc. The compacted collagen of MD‐FPCL lattice exhibits a strong birefringence pattern due to organized collagen fiber bundles. In contracted HD‐FPCL, a minimal birefringence develops, indicating minimal organization of collagen fiber bundles. MD‐FPCL contraction was reduced with less than 10% serum; the disruption of microtubules, uncoupling of gap junctions, inhibition of tyrosine kinases, and addition of a blocking antibody to α2β1 collagen integrin. Making HD‐FPCL with only 1% serum or including the inhibitory agents had only minimal affect on lattice contraction. On the other hand, platelet‐derived growth factor stimulated HD‐FPCL contraction but had no influence on MD‐FPCL contraction. It is suggested that the mechanism for HD‐FPCL contraction is limited to the process of cells spreading. HD‐FPCL contraction is independent of collagen organization, microtubules, gap junctions, α2β1 integrin, and tyrosine phosphorylation. MD‐FPCL contraction involves collagen organization and is optimized by the involvement of microtubules, gap junctions, α2β1 integrin, and tyrosine phosphorylation. When studying cell physiology in a collagen matrix, cell‐density influences need to be considered. J. Cell. Physiol. 185:432–439, 2000. © 2000 Wiley‐Liss, Inc.