Freeze-fracture replica studies of the human adrenal cortex, with special references to microvillous projections.

Freeze-fracture replicas of human adrenocortical cells revealed en face fractures (both P and E faces) of the cell surface to be classified into three patterns: (1) the fracture face with no microvillous projections; (2) the fracture face mainly with short microvillous projections which arise horizontally from the edges of the small cavity on the cell surface to form a flower bud-like configuration on the P face; (3) the fracture face mainly with varying-sized, longer microvillous projections which arise almost vertically from the cell surface and show no specific organization. The former two fracture faces were supposed to correspond to the plasma membranes facing the interstitium including pericapillary spaces, since they had no gap junctions and frequently appeared along sinusoidal capillaries. On the other hand, the latter fracture face seemed to be equivalent to the plasma membranes facing intercellular spaces, since it frequently showed gap junctional specialization of intramembranous particles and usually both the P and E fracture faces of plasma membrane on the same surface. En face fractures of these gap junctions were various in shape and size. Tight junctions and their complex form with gap junctions were not encountered. Cell organelles and the nucleus had more numerous intramembranous particles on the P fracture face than on the E fracture face.