The interface between epithelium and lamina propria in the rat urinary bladder.

We investigated by transmission and scanning election microscopy the interface between the epithelium and lamina propria in the rat urinary bladder. A digestion technique that dissolves the basal laminae and collagen fibrils was effective in cleaving the mucosa at this level; the specimens were then prepared for scanning electron microscopy, thus visualizing the basal epithelial surface and the uppermost surface of the lamina propria. The underside of the epithelium is scored by very numerous grooves which in the intact organ are occupied by a dense network of blood capillaries. These vascular grooves allow a large number of capillaries (epithelial capillaries) to run at a distance of a few tenths of a micron from the epithelium. On the side of the lamina propria, after collagen and other extracellular materials had been removed, the capillary network itself is visible in the uppermost region. The network is complementary to that of vascular grooves. Other smaller grooves on the basal surface of the epithelium correspond to nerve fibres which run within a few tenths of a micron from the epithelium.