Glomerular permeability of macromolecules. Effect of molecular configuration on the fractional clearance of uncharged dextran and neutral horseradish peroxidase in the rat

Molecular parameters other than size and charge are likely to influence the filtration of macromolecules across the glomerular filter. We have studied, therefore, the glomerular permeability of macro-molecules with widely different molecular configuration such as horseradish peroxidase, a plant glycoprotein with an isoelectric point in the physiologic pH range, and dextran, an uncharged sugar polymer of D-glucopyranose. Simultaneous fractional clearances were determined for both test macromolecules in five Wistar-Furth rats. The results indicate that for a molecular radius of 28.45 Å, as measured by gel filtration, the sugar polymer has a fractional clearance of 0.483 on the average, exceeding that of the protein tracer, with a value of 0.068, by a factor > 7. We conclude that other molecular parameters such as shape, flexibility, and deformability play important roles in the transport of macromolecules across the extracellular matrix that constitutes the glomerular filter.