Structural investigation of loose connective tissue by using a series of dextran fractions as non-interacting macromolecular probes.

The ability of the uncharged open-coil dextran molecules to penetrate tissue space, without coil-shape change, was utilized to probe (by partitioning experiments) the structural arrangement of the collagen-fibre network and the proteoglycan system. Hyaluronidase digests most of the proteoglycans away and enables the respective contributions to the exclusion volume to be evaluated by using a series of different-molecular-weight dextrans. It appears that the major part of the exclusion volume is due to the collagen-fibril as a rod and the dextran coil as an impenetrable sphere. The additional exclusion due to the proteoglycans could be accounted for by a set of points (regions of high proteoglycan-segment density) over which the dextran coild cannot pass. These points are an average of 50 nm apart and are indicative of local extensive entanglement of high-molecular-weight proteoglycans with each other. Reasons are given why these entanglements could not act as cross-links in long-term elastic loading of the tissue.