Freeze-fracture investigations of membranes of flask cells in the kidney and of parietal cells in the stomach of claw-frog (Xenopus laevis)

The flask cells of the nephron and the parietal cells in the stomach fundic glands of claw-frog show some structural similarities such as the existence of a canalicular system, the richness of mitochondria and numerous small cytoplasmatic vesicles. Both cell types also seem to have common functional pecularities. With the freeze-fracture method the cell membranes of both cell types showed a richness of intramembrane particles (IMPs) and the existence of special elongated IMPs especially in the apical and canalicular cell membranes. In the flask cells the elongated so-called rod-shaped IMPs measured 29 X 13 nm and were very numerous, whereas the corresponding particles in the parietal cells in the same membranes were smaller (13 X 5 nm) and not so numerous. The similarities and differences between the membranes of both cell types are discussed in relation to the cell function.