Measurements of isolated glomerular albumin permeability do not change in a variety of proteinuric conditions

Albuminuria is the hallmark of glomerular disease. The oncometric assay of glomerular albumin permeability A has been used to measure glomerular reflection coefficient to albumin (σ alb ) in clinically‐relevant circumstances A . We have previously reported theoretical limitations of this assay B , and here report practical assay limitations. Single glomeruli, isolated by graded sieving, were held on an aspiration pipette. Glomerular volume (V) was recorded during incubation in BSA solution (V alb ) of known oncotic pressure. The incubating solution was exchanged for an iso‐oncotic solution of dextran molecules (>100kDa MW after dialysis), and glomerular volume was remeasured (V dex ). V dex /V alb describes σ alb . σ alb was measured in healthy mouse glomeruli before and after exposure to pronase and protamine. No changes were observed (pronase: pre 0.99±0.02; post 0.99±0.01 (7); p>0.9) (protamine: pre 0.95±0.01; post 0.95±0.01 (7); p>0.8). In addition, σ alb was not different between glomeruli from mice with (0.95±0.03 (30)) or without (0.95±0.02 (24)) streptozotocin‐induced diabetic albuminuria (p>0.7), nor between glomeruli from rats with (1.00±0.01 (9)) or without (0.99±0.01 (8)) spontaneous proteinuria (p>0.6). We conclude that this assay is inadequate for glomerular albumin permeability measurements.