The chemoreceptor surface of the taste organ in the frog Rana esculenta. A freeze-fracture analysis.

The epithelial surface of the taste disc on the fungiform papillae of the frog was studied by means of freeze-fracture and conventional electron microscopy. The plasma membrane of the apical process of taste receptor cells was found to exhibit a uniform population of 10-nm intramembrane particles on its fracture face P in a density of 1,000-1,800/micrometers2. In contrast to intramembrane particles in mucous cells or in other regions of the plasma membrane, these particles were observed to protrude approximately twice as high from the fracture face. Not more than 1-2% of the particles were found on fracture face E of the apical process of the taste cell. The apical regions of satellite and mucous secretory cells are also described. The occurrence of relatively large intramembrane particles in a membrane region presumed to function as the chemoreceptor area of taste cells suggests that the particles may be involved in chemoreception.