Ultrastructural observation of paracrystalline aggregates of microtubules in anterior pituitary cells of the chinchilla (Chinchilla laniger).

Unusual paracrystalline aggregates of microtubules which have not been described in any other mammalian species were observed in cultured anterior pituitary cells of normal chinchillas as well as in situ in the pituitary glands of these animals. These aggregates appeared as regularly arranged tubular structures in the longitudinal plane, and as a checkerboard pattern of closely and regularly packed microtubules when examined in transverse section. Supplementation with vinblastine, colcemide or colchicine in the culture medium did not change these structures morphologically. Each unit of tubules consisted of an outer wall or parallelogram profile and an inner wall composed of a single hexagonal doublet or in a figure "8"form. The outer wall of the parallelogram was 35 X 28 nm in length for both sides, while the diagonal of the inner wall was 18 X 28 nm. These paracrystalline aggregates of microtubules in the chinchilla pituitary cells are morphologically distinct from the paracrystalline assembly of cytoplasmic microtubules induced by vinblastine or other alkaloids. The function and significance of these paracrystalline aggregates in anterior pituitary cells of the chinchilla are uncertain.