Fine structure of the urinary bladder of the bullfrog, (Rana catesbiana)

The urinary bladder of the bullfrog, Rana catesbiana has been studied by light and electron microscopy. Three epithelial cell types were found: (1) granular cells, (2) mitochondria‐rich cells, and (3) basal cells. The structure of the Rana catesbiana bladder differs from that of the toad Bufo marinus, in several respects: it lacks a mucous (goblet) cell type, its granular cells do not contact the underlying basement membrane, it has specialized, smooth‐muscle cell‐basal epithelial cell contacts, not previously described in amphibian bladders, and its mucosa is richly innervated. Mitochondria‐rich cells within the bullfrog bladder epithelium were occasionally observed touching the basement membrane. The specialized smooth muscle‐basal cell contacts provide anatomical evidence for how regulatory vasoactive substances such as neurohypophyseal peptides might alter epithelial geometry. Many nerve endings invest the mucosa just beneath the epithelial basement membrane in proximity to mitochondriarich cells and basal cells. The possible role of neural regulation in epithelial transport was discussed.