Biomedical subjects

M F Smit

Publications and source records attributed to M F Smit.

3 recordsLinked to original sources

PubMed1997

Competition between polyanions in glomerular binding and renal clearance.

This study tests the hypothesis that exogenous polyanions may accumulate in the glomerular capillary wall and thereby provide fixed negative charges that will be effective, through electrostatic interactions, in governing the transcapillary transport of charged molecules. We have tested the effects of high concentrations of dextran sulfate, heparin, and orosomucoid on the fractional clearance of albumin and dextran sulfate using the isolated perfused kidney technique. We demonstrate that all these exogenous polyanions are without effect on the fractional clearance of albumin. Augmentation of glomerular charge through the binding of dextran sulfate or orosomucoid is very small compared to the charge augmentation by albumin. These results agree with previous studies which demonstrate that electrostatic interactions governing glomerular transcapillary wall transport are negligible. This study also demonstrates that there is no plausible correlation between the fixed negative charge contributed by endogenous metabolically labeled glomerular heparan sulfate and the manifestation of apparent charge selectivity as determined with dextran sulfate. The results are also consistent with previous studies that the renal processing of both dextran sulfate and albumin is associated with specific cellular uptake.

Animals↗

PubMed1996

A codiffusing system as a novel model for capillary wall charge selectivity.

The electrostatic interaction associated with polyion-polyion interaction has been thought to be the basis for the differential transport of charged transport probes across the capillary wall. The charge of the transport probe may interact with the negative charges of capillary wall cell surfaces and the intercellular glycocalyx or extracellular matrix. This study has set out to quantitate the exact nature of the polyion-polyion interaction through the theoretical and experimental study of the partition-diffusion of albumin in solutions of anionic polysaccharides (dextran sulfate or heparin) at concentrations up to 250 meq 1(-1) or at an average intercharge distance of 2.2 nm, as compared with solutions of uncharged dextran at the same volume concentration. The results demonstrate that the albumin partition-diffusion is exactly the same in dextran sulfate, heparin and uncharged dextran matrices of the same polymer volume fraction. These results confirm previous studies from this laboratory that the charge effect through polyion-polyion interaction under physiological conditions is negligible.

Albumins↗

PubMed1995

Albumin interaction with the glomerular capillary wall in vitro.

The binding of albumin to the glomerular capillary wall was studied using albumin-gold in perfused kidneys, the interaction of [3H]albumin with isolated glomeruli at 37 degrees C and 4 degrees C and the interaction at [3H]albumin with purified basement membrane. The albumin-gold was found to bind predominantly to the basement membrane and this interaction could be dissociated with high concentrations of albumin. There was binding of albumin to isolated rat glomeruli which exhibited temperature dependence. Glomeruli exhibited a binding site at both 37 degrees C and 4 degrees C with an association constant in the range of 1 to 3 x 10(4) M-1 that bound 7 x 10(13) molecules/glomerulus. At 37 degrees C, however, there was anomalous Scatchard binding behaviour at relatively higher concentrations of albumin (30 to 50 mg/ml) which could be due to either glomerular cell uptake or the appearance of multiple binding sites or both. The binding of albumin to isolated glomeruli and the glomerular albumin levels in isolated kidney perfusion could largely be accounted for by the binding of albumin to the glomerular basement membrane. The albumin binding to glomeruli at 37 degrees C was enhanced by Pronase digestion and heparinase digestion, but remained unchanged following trypsin treatment or neuraminidase treatment. Similarly, albumin was shown to bind to purified basement membrane preparations. This binding was also enhanced (approximately 80 times) by heparinase digestion but remained unchanged after digestion with chondroitinase ABC or hyaluronidase.(ABSTRACT TRUNCATED AT 250 WORDS)

Albumins↗