The Rat Glomerular Filtration Barrier Does Not Show Negative Charge Selectivity

ABSTRACT Objective: To characterize the effects of size, shape, and negative charge on the transport of macromolecules across the glomerular capillary wall by using the sieving curves (fractional clearance vs. solute molecular radii) of fluorescent polydispersed polysaccharide tracers. Methods: Glomerular fractional clearances (FC) were measured with fluorescent neutral [isoelectric point (pI) = 7.3 ± 0.2] and negatively charged (pI = 3.5 ± 0.4) dextrans (DEX) in comparison with negatively charged (pI = 4.8 ± 0.3) hydroxy ethyl starch (HES) and (pI = 4.6 ± 0.1) bovine serum albumin (BSA) in Sprague‐Dawley and Fischer 344/Brown Norway rats. FCs (n= 53) were measured by using the urinary clearance of 14C‐inulin to determine the glomerular filtration rate. The relative uptake of each fluorescent probe by endothelial and renal proximal tubule epithelial (LLC‐PK1) cells, in vitro, was measured microscopically by using a cooled (−25 °C) CCD camera. Results: The sieving curves for randomly coiled neutral and negatively charged DEX probes were identical. These FC values were 6‐fold greater than those for HES and 200‐fold above similarly sized fluorescent BSA. The polysaccharide probes did not show significant binding to serum proteins. The uptake of BSA by LLC‐PK1 cells was 20‐ to 100‐fold greater than that for neutral or negatively charged macromolecules. Conclusions: These findings indicate that the rat glomerular filtration barrier restricts the transport of polysaccharide macromolecules as a function of their size and configuration but not negative charge.