Three-dimensional network of microtubules in secretory ameloblasts of rat incisors

Secretory ameloblasts appear to contain isolated microtubules and microtubules arranged in bundles associated with filaments or sheets of filaments. The relation between isolated and bundled microtubules in secretory ameloblasts was investigated by serial sections. Some isolated microtubules entered microtubule bundles in adjacent sections. Microtubules which diverged from a bundle sometimes converged into another bundle in other sections. Microtubules were associated with filaments or sheets of filaments for varying distances. It is concluded that isolated microtubules frequently form bundles by joining with other microtubules, and thus, microtubules make a three-dimensional network throughout the whole cytoplasm which is probably concerned with the transport of secretion granules.