Stereoscopic study of renal proximal tubular basement membrane by quick-freezing and deep-etching method.

Rat kidney tissue was quickly frozen, fractured and deeply etched. A replica was prepared by shadowing with platinum and carbon. The proximal tubular basement membrane was found to be different from that in conventional ultrathin sections. The lamina lucida was not electron translucent but filled with a traversing filamentous structure, which connected the tubular cell membranes with the lamina densa. The lamina densa had a three-dimensional polygonal meshwork structure. This meshwork was composed of fibrils (6-9 nm in thickness). In the lamina reticularis, collagen fibrils and micro-threads formed a loose network structure. The traversing filamentous structure in the lamina lucida might serve as an anchorage for the cell membranes and extracellular matrices.