Freeze-fracture study of taste bud pores in the foliate papillae of the rabbit.

In freeze-fractured specimens of taste buds from the foliate papillae of rabbits, the intercellular spaces are separated from the pore of the taste bud by zonulae occludentes of the "tight-type". Below these tight junctions numerous desmosomes are found at irregular intervals. The epithelial cells adjacent to the pore are also joined by single strands of fusion. The microvilli arising from the neck of the type I cells have a high particle density. The microvilli of type II cells and especially the short microvilli of peripherally situated cells have a lower intramembranous particle density. The single microvillus of type III cells has a very large diameter and is longer than the other microvilli. It contains a few larger intramembranous particles and vesicle-like protrusions of the membrane facing the cytoplasm. Transverse fracturing reveals a filamentous fine structure in all microvilli. The physiological implications of these observations are discussed.