References
- , A pore in the ECM is regarded as an extracollagenous, extrapolysaccharide space, or opening, of undefined geometric shape.
- , There is no evidence to suggest that bulk water structure is altered in these polysaccharide domains.3,4. The often used term, “water binding properties,” of ECM polysaccharides or proteoglycans is misused and confusing. The fact that proteoglycans occupy large hydrated domains is derived from the tendency of the polysaccharide chains of the proteoglycan to diffuse. This can be rationalized in terms of the thermodynamic and hydrodynamic properties of segments of the polysaccharide chain (see section on Translational Hydro-dynamic Frictional Coefficient).
- Maroudas A., Venn M. Chemical composition and swelling of normal and osteoarthritic femoral head cartilage. Ann. Rheum. Dis. 1977; 36: 390–403
- Comper W. D., Laurent T. C. Physiological function of connective tissue polysaccharides. Physiol. Rev. 1978; 58: 255–315
- , There are a number of different terms used in the literature to describe translational diffusional motion; these include mutual diffusion, segment diffusion, tracer self diffusion, and cooperative diffusion. All these types of diffusion measure displacement of the diffusing molecule relative to solvent but may vary under the conditions with which they are measured and the nature of the concentration gradient and absolute concentration. The diffusional motion of biological significance is that representing the motion of the molecule with respect to water and includes the equivalent terms mutual, segment and cooperative diffusion coefficients.
- , In order to simplify the presentation, some of the equations used here have been abbreviated. For rigorous equations see references 7 and 8.
- Comper W. D., Preston B. N., Daivis P. The approach of dextran mutual diffusion coefficients to molecular weight independence in semi dilute solutions of polydisperse dextran fractions. J. Phys. Chem. 1986; 90: 128–132
- Williams R. P W., Comper W. D. Osmotic flow caused by nonideal macromolecular solutes. J. Phys. Chem. 1987; 91: 3443–3448
- Kantor T. G., Schubert M. A method for the desulfation of chondroitin sulfate. J. Amer. Chem. Soc. 1957; 79: 152–153
- Comper W. D., Williams R. P W. Hydrodynamics of concentrated proteoglycan solutions. J. Biol. Chem. 1987; 262: 13464–13471
- Zamparo O., Comper W. D. Hydraulic conductivity of chondroitin sulfate proteoglycan solutions. Arch. Biochem. Biophys. 1989; 274: 259–269
- , Sedimentation-equilibrium experiments cannot be employed to measure II at concentrations 40 mg ml−1 due to the formation of high refractive index gradients. Equilibrium dialysis against polymer solutions of known osmotic activity suffer from possible errors (particularly at high concentrations) associated with salt exclusion by the polymer. These errors will effect osmotic pressure determinations of polyelectrolytes even more so. Sedimentation-diffusion studies have the disadvantage that at high concentrations (80 mg ml−1) the sedimentation is extremely slow and that osmotic resistance to flow may become significant for centrifugal fields attainable in analytical ultracentrifuge.
- Wells J. D. Salt activity and osmotic pressure in connective tissue. 1. A study of solutions of dextran sulphate as a model system. Proc. R. Soc. London. B. 1973; 183: 399–419
- Urban J. P G., Maroudas A., Bayliss M. T., Dillon J. Swelling pressures of proteoglycans at the concentrations found in cartilagenous tissues. Biorheology 1979; 16: 447–464
- Soodak H., Iberall A. Am. J. Physiol. 1978; 235: R3–R17, A similar conceptual model for solute-solvent exchange in association with membrane transport has been discussed by, Osmosis, diffusion, convection.
- Williams R. P. W., Comper W. D. Osmotic flow caused by polyelectrolytes. Biophys. Chem. 1990, in press
- , An interesting situation arises as to the mechanism of osmotic equilibration between two solutions of identical osmotic pressure but different f12. In this case there will be significant cross-diffusion across the length of the membrane to balance the respective frictional coefficients. It does imply that the mobility of solutes at one surface of the membrane will be affected by the solute on the other side of the membrane. This will not apply to solutes in the bulk solution. Therefore the membrane may endow molecules near the membrane surface with different properties, in terms of mobility, as compared to the bulk solutions.
- Scott J. E. Proteoglycan-fibrillar collagen interactions. Biochem. J. 1988; 252: 313–323
- Maroudas A. Biophysical chemistry of cartilagenous tissues with special reference to solute and fluid transport. Biorheology 1975; 12: 233–248
- Deen W. M., Stavat B., Jamieson I. M. Theoretical model for glomerular filtration of charged solutes. Am. J. Physiol. 1980; 238: F126–F139
- , An approximate estimate of the contribution of the collagen fibrous network of the GBM to hydraulic conductivity can be estimated for rat GBM using the Poiseuille relationship22 where where ris the effective pore radius of the capillary wall and l the thickness of the membrane; with r = 50 10−8 cm and l = 150 10−7 cm gives k = 3.12 10−14 cm2. This calculation gives a low k lvalue (see text) and would suggest that the collagen network may play a significant role in affecting water transport across the GBM.
- Brenner B. M., Dworkin L. D., Ichikawa I. Glomerular filtration. The Kidney, B. M. Brenner, F C. Rector. W. B. Saunders, Philadelphia 1986; 124–144, ch. 4
- , Specific hydraulic conductivity and osmotic pressure data on GBM heparan sulfate are difficult to perform due to small quantities of heparan sulfate that can be isolated. A reasonable approximation of these quantities seems to be drawn from data on heparin as its k-data and diffusion data appear to be very similar to desulfated heparin. This demonstrates that range of heparin-like polysaccharides, ranging from heparin to low-sulfated heparan sulfate, will have similar hydrodynamic properties.
- Deen W. M., Troy J. L., Robertson C. R., Brenner B. M. Dynamics of glomerular ultrafiltration in the rat. IV Determination of the ultrafiltration coefficient. J. Clin. Invest. 1973; 52: 1500–1508
- Zamparo O., Comper W. D., submitted for publication