Isolation and Ultrastructure of Human and Bovine Renal Tubular Basement Membranes

Human and bovine tubuli were isolated by the passage of renal cortices through a series of stainless steel sieves of varing pore sizes. Tubular basement membrane (TBM) was isolated from tubuli either by sonic disruption or detergents. Observation on ultrathin sections of the final pellets isolated by both methods confirmed that pure TBM was obtained. Using electron microscopy after negative staining, human and bovine TBM isolated and observed under different conditions were shown to be a fine meshwork composed of pores and strands. The average diameter of the pores varied among samples. The diameter of the pores was approximately 4-7 nm in human and 4-8 nm in bovine TBM. For ultrastructural study, sonication has the advantage that the basement membranes retained their native structure to a larger degree, whereas the molecular sieve of basement membranes was sometimes destroyed by the treatment with detergent.