Cellular contributions to glomerular size-selectivity.

The glomerular capillary wall permits free passage of low-molecular-weight solutes, while severely restricting large proteins. Although both cell layers (endothelium and epithelium) almost certainly contribute to this size-selectivity, their relative importance has been difficult to assess. The finding by Rippe et al. of an inverse relationship between the sieving coefficient of Ficoll and glomerular filtration rate sheds light on this.