TRANSPORT OF SOLUTES THROUGH CARTILAGE - PERMEABILITY TO LARGE MOLECULES

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  • 1 January 1976
    • journal article
    • research article
    • Vol. 122  (NOV) , 335-347
Abstract
General data relating to the partition and diffusion of small ionic and non-ionic solutes are briefly reviewed; the main topic is the partition and diffusion of large protein molecules such as serum albumin and IgG [immunoglobulin G]. Methods, using radioactively labeled iodinated proteins, are described, both for the partition and the diffusion experiments [in mammals]. Particular emphasis is laid on the separation after desorption from the tissue of free 125I from the protein-bound (125I) iodine, as the penetration of the former into cartilage can be a serious source of error in this type of study. The diffusion coefficients of large molecules were determined by an efflux procedure, rather than by the membrane technique which was previously employed for the smaller solutes. The partition coefficients of the globular proteins apparently decrease with molecular size up to serum albumin. The partition coefficient of IgG, is of the same order of magnitude as that of serum albumin although IgG is much larger than serum albumin. A possible explanation is that there is a small fraction of pores in cartilage which are larger than the rest and that the transport of the very large molecules may be taking place predominantly through these. The diffusion coefficient of serum albumin in cartilage is equal to about 1/4 of its value in aqueous solution and this relatively high value may again be related to transport through a small fraction of larger pores. The partition coefficients of large molecules decrease very steeply with increase in the glycosaminoglycan content of the tissue.