Scanning electron microscopy of isolated dog renal tubules

Isolation of canine renal tubular segments, cell clusters and individual cells permits direct observation by scanning electron microscopy (SEM) of the three dimensional cell shapes and the complex lateral and basal labyrinth structures. These functionally vital areas of the various tubular segments have not been previously observed in such detail. The tubular segments were freed of the obscuring basement membranes by prolonged tryptic digestion of tissue perfusion-fixed with glutaraldehyde, followed by attachment to gelatine coated coverslips and preparation for SEM. The tubular basal labyrinth is found to consist of a mosaic of basal processes arising from the lateral processes and the base of the cell body. The lateral processes and basal processes interdigitate with adjacent cells. Each tubular segment exhibits its own characteristic patterns of basal processes. The basal processes of the proximal convoluted tubule (PCT) are shaped like an inverted anvil, often branching. The basal processes of the proximal straight tubule (PST) and thin limbs are short microvilli. The distal straight tubule (DST) have fishtail-like basal processes. The distal convoluted tubule (DCT) show a swirling mixture of anvil shaped and microvillous basal processes. The collecting ducts exhibit short basal microvilli, plicae and villi lined basal infoldings. The looser structure of the basal labyrinth of cell clusters and isolated cells produced by this isolation procedure facilitated recognition of these complex structures.