Osmotic flow caused by chondroitin sulfate proteoglycan across well-defined nuclepore membranes

Osmotic flows generated by solutions of Swarm rat chondrosarcoma proteoglycan subunit have been analysed using Nuclepore membranes of well-defined straight-through cylindrical pores of known radius rp. Membranes with rp in the range of 27-500 nm were studied. For semipermeable membranes, which are impermeable to the proteoglycan, the flows were consistently related to r2p and not to r4p (Poiseuille's Law) which demonstrates that the flow is a diffusion-controlled process as described previously (R.P.W. Williams and W.D. Comper, J. Phys. Chem. 91 (1987) 3443). We have also identified a characteristic distance, approx. 50% of the average interparticle spacing, out from the pore surface of the membrane over which the proteoglycan has to move to generate flow. The proteoglycan generates similar osmotic permeability coefficients with membranes up to 125 nm in pore diameter which is significantly larger than the average intermolecular distance. These results have been interpreted in terms of the membrane pore recognising dynamic transient aggregates in the proteoglycan solution.