Muciliary transport in newt lungs: the ultrastructure of the ciliary apparatus in isolated epithelial sheets and in functional triton-extracted models

High voltage and conventional electron microscopy were used to investigate the ultrastructure of the ciliary apparatus in intact and in Triton-extracted, reactivated sheets of mucociliary epithelium isolated from newt lung. Each long (about 13 microns) ciliary axoneme terminates on a barrel-shaped basal body which is anchored in the apical cytoplasm by a variety of accessory structures. A basal foot is associated with the midpoint of each basal body and acts as a focal point for numerous microtubules (MTs). In many cases MTs can be seen to interconnect the feet of neighbouring basal bodies. Attached to the proximal end of each basal body and extending in a direction opposite the basal foot is a large 'ciliary root'. Each ciliary root is associated with a distinct bundle of 6-7 nm microfilaments which appear to stain with the specific F-actin probe NBD-phallacidin. A single 3-4 microns long striated rootlet inserts into each ciliary root and extends toward the cell nucleus through an extensive network of microfilaments. At the level of the basal plate 'Y-shaped' structures appear to connect each axonemal outer doublet MT to the plasma membrane. All of these ciliary accessory structures are present in the same relationship in Triton-extracted models. Their morphology and distribution indicates that they serve to anchor the cilia in the apical cytoplasm. In addition some of these structures appear to be responsible for maintaining the structural and functional integrity of the ciliary field in the demembranated and reactivated models.