Glomerular size and charge selectivity in the rat as revealed by FITC-Ficoll and albumin

The fractional clearances (θ) for FITC-Ficoll and albumin were estimated in isolated perfused rat kidneys in which the tubular activity was inhibited by low temperature (8°C) and/or 10 mM NH4Cl. The Ficoll data were analyzed according to a two-pore model giving small and large pore radii of 46 A and 80–87 A, respectively. The estimated negative charge density was 35–45 meq/l at 8°C. Perfusion with erythrocyte-free solutions of kidneys at 37°C reduced glomerular size and charge permselectivity. Thus the large pore fraction of the glomerular filtrate (fL) was 1.64% at 37°C compared with 0.94% at 8°C. The θ for albumin was four times higher at 37°C than at 8°C (0.86% vs. 0.19%, respectively). NH4Cl caused further irreversible damage to the glomerular barrier. We conclude that there are no deleterious effects on the glomerular barrier of a reduction in temperature from 37°C to 8°C. Therefore our data seem to disprove the hypothesis of low glomerular permselectivity and transtubular uptake of intact albumin an...