Similarity of permeabilities for Ficoll, pullulan, charge-modified albumin and native albumin across the rat peritoneal membrane D. Asgeirsson, J. Axelsson, C. Rippe and B. Rippe Department of Nephrology, Clinical Sciences, Lund University, Lund, Sweden Received 13 September 2008, revision requested 15 October 2008, final revision received 22 December 2008, accepted 1 January 2009 Correspondence: B. Rippe, University Hospital of Lund, S-211 85 Lund, Sweden. E-mail: bengt.rippe@med.lu.se Abstract Aim: Compared to neutral globular proteins, neutral polysaccharides, such as dextran, pullulan and Ficoll, appear hyperpermeable across the glomer- ular filtration barrier. This has been attributed to an increased flexibility and/ or asymmetry of polysaccharides. The present study investigates whether polysaccharides are hyperpermeable also across the continuous capillaries in the rat peritoneum. Methods: In anaesthetized Wistar rats, FITC–Ficoll or FITC–pullulan together with 125 I-human serum albumin (RISA) or neutralized 125 I-bovine serum albumin (nBSA) were given intravenously, after which peritoneal dialysis (PD) using conventional PD fluid (Gambrosol 1.5%) was performed for 120 min. Concentrations of FITC-polysaccharides and radioactive albumin species in plasma and dialysis fluid were analysed with high- performance size exclusion chromatography and a gamma counter respec- tively. Transperitoneal clearance values were calculated for polysaccharides in the molecular radius range 36–150 A ˚ , and for RISA and nBSA. Results: Ficoll and pullulan showed more or less identical permeabilities, compared to RISA and nBSA, across the peritoneal membrane. Although RISA-clearance, 5.50  0.28 (lL min )1 ; SEM), tended to be lower than the clearances of Ficoll 36A ˚ (6.55  0.25), pullulan 36A ˚ (6.08  0.22) and nBSA (6.56  0.23), the difference was not statistically significant. This is in contrast to the hyperpermeability exhibited by polysaccharides across the glomerular filtration barrier and also contrasts with the charge selectivity of the latter. Conclusion: The phenomenon of molecular flexibility is more important for a macromolecule’s permeability through the glomerular filter than across the continuous peritoneal capillary endothelium. Furthermore, it seems that charge plays a subordinate role in the steady-state transport across the combined peritoneal capillary–interstitial barrier. Keywords capillary, glomerular filtration barrier, permeability, physiology. Globular proteins and polysaccharides have been exten- sively used as molecular probes to study the permselec- tivity of capillary walls (Taylor & Granger 1984, Rippe & Haraldsson 1994, Michel & Curry 1999, Venturoli & Rippe 2005). The biological barrier that solutes and water have to traverse in the glomerular filter is quite different from that of most other blood-tissue barriers in the body. In the glomerulus, the urinary space is separated from the blood by a thin, but complex, barrier made up of the highly fenestrated endothelial cell wall, the glomerular basement membrane (GBM) and the filtration slits in between the foot processes of Acta Physiol 2009, 196, 427–433 Ó 2009 The Authors Journal compilation Ó 2009 Scandinavian Physiological Society, doi: 10.1111/j.1748-1716.2009.01955.x 427