Apical secretion from taste bud and other epithelial cells in amphibians.

Taste buds of the axolotl, Ambystoma mexicanum, contain cells, previously undescribed in this species, which have a long apical process, and are similar to the Type III cells of mammalian taste buds, and to the gustatory cells in fish. In the supporting cells, there is evidence of periodic decapitation, in addition to secretion by exocytosis. Bilaminar fragments, which are leaf-shaped bodies formed of two dense laminae separated by a lucent gap, protrude from the apical microvilli of the supporting cells and are found detached in the extracellular secreted layer. Their form and dimensions suggest that they represent secreted lipo-protein material. Similar bilaminar fragments have been seen, in much smaller numbers, on some other epithelial cells in amphibians, and in fish. A unique case, in which rough endoplasmic reticulum was found in the extracellular layer of the axolotl oral epithelium, is reported; it had apparently been ejected from the cell. It is suggested that the axolotl produces a copious secretion at the taste bud pore, in order to wash the surface, and that the bilaminar fragments represent material aiding this cleansing process. The condition in the axolotl is compared with that in some other species, particularly Rana temporaria.