Abstract
In order to clarify the distribution of cholesterol in plasma- and cytomembranes of secretory cells of the anterior pituitary and adrenal medulla, freeze-fracture images of the filipin-treated tissues were observed.
The distribution of cholesterol in all the secretory cells of these organs shows almost the same pattern. The filipin-sterol complexes are distributed somewhat heterogeneously but in moderately high density on the fractured plasma membranes of all the cells examined. The small shallows on the plasma membrane, corresponding to coated pits and showing aggregates of membrane particles (MP), lack the complexes. The limiting membranes of almost all the secretory granules are very rich in complexes.
The membranes of rough endoplasmic reticulum, nucleus, mitochondria, and Golgi apparatus, which are considered to contain rich enzymatic protein and have active functional properties, are very poor in distribution of cholesterol, though small clusters consisting of a few complexes are scattered in these organelles except for mitochondria. In the traps-side of the Golgi apparatus, where the immature secretory granules arise, the complexes are relatively denser in distribution as compared with those of the cis-side.
