Meshwork structures in bovine glomerular and tubular basement membrane as revealed by ultra-high-resolution scanning...

We examined the ultrastructure of the bovine glomerular basement membrane (GBM) and tubular basement membrane (TBM) using ultra-high-resolution scanning electron microscopy after conductive staining without metal coating. Purified basement membranes (BMs) were obtained by sonication and acellular BMs by detergent treatments. Purified GBMs (PGBMs) and acellular GBMs (AGBMs) showed similar meshwork structures composed of regular round or oval pores and branching strands. Pore diameters were 10.2 +/- 2.4 nm (mean +/- SD) in PGBMs and 9.8 +/- 3.1 nm in AGBMs. Purified TBMs (PTBMs) and acellular TBMs (ATBMs) exhibited heterogeneous meshwork structures in which compact meshes in the cristae were combined with coarse meshes in the invaginations on the epithelial surfaces. Pore diameters were 12.6 +/- 5.2 nm in PTBMs and 11.4 +/- 4.0 nm in ATBMs which were significantly larger than those in GBMs. The width of the strands ranged from 3 to 15 nm in all BMs. A 4 M guanidine hydrochloride extraction of the acellular BMs revealed large polygonal networks in the invaginations of the TBM and twisted strands which were considered to be type IV collagen fibrils. Ultra-high-resolution scanning electron microscopy and conductive staining were useful for the study of three-dimensional architectures of BMs and revealed heterogeneous meshwork structures in the GBM and TBM which were probably caused by a different ratio of the major components.