ASGSB 1999 Annual Meeting Abstracts

EFFECT OF LOAD ON COLLAGEN GEL CONTRACTION BY RAT TENDON FIBROBLASTS AND OSTEOBLASTS/OSTEOCYTES IN VITRO. B. Johnson-Wint. Dept of Biological Sciences, Northern Illinois Univ, DeKalb IL.

Cells in tendon and bone physically move type I collagen fibers to determine the shape and strength of these tissues. A model culture system I was used to investigate the possibility that load influences type I collagen packing by the cells in tendon and bone. Foot tendon fibroblasts and metatarsal osteoblasts/osteocytes from young adult rats were grown for 4-6 passages in culture and assayed for their ability to organize collagen I fibers in a contracting collagen gel assay.  Cell embedded cylindrical type I collagen gels were hung by one end on hooks in a vertical tissue culture chamber and were maintained submerged in culture medium at 37C. Weights were attached to the other end of the cylindrical gels. Gels contained 1.25x10⁵ cells and 245 µg collagen. Cell mediated contraction of the collagen gel was monitored by measuring diameter and length of the gel at appropriate time intervals. Experimental gels were fixed and pre-pared histologically for viewing with a light microscope. Both cell types contracted the diameter and length of unloaded cylindrical collagen gels retaining the cylindrical shape in reduced size and increased collagen density. Tendon fibroblasts completed gel contraction in 24 h at which time diameter, length and volume of the cylinder were 50%, 50% and 12.5% respectively of starting size. Osteoblasts/osteocytes took 48 h to contract the collagen gel.  By 24 h the cylinder diameter, length and volume were 67%, 77% and 34% respectively of starting size.  Collagen gels without embedded cells did not contract. Cell embedded cylindrical collagen gels were loaded in their long dimension by hanging weights ranging from 6.5 to 97.9 mg on the free end of the gel. Tendon fibro-blasts lifted weights up to 18.8 mg during gel contraction. The same number of osteoblasts/osteocytes were unable to lift any of the experimental weights or contract in the long dimension when loaded.  Both cell types contracted loaded cylindrical collagen gels in diameter. Histological sections showed that tendon fibroblasts in an unloaded gel are multipolar and randomly oriented whereas cells in a loaded gel are bipolar and oriented with long axis parallel to the direction of load.  These results demonstrate that cell orientation in and the final shape of a contracting cell populated collagen gel is influenced by load on the gel, and that tendon fibroblasts exert more force per cell while contracting a collagen gel than osteoblasts/osteocytes.

Back to Meeting Program