Surface morphology of normal and enzymatically treated rat parotid gland

The surface morphology of the rat parotid gland was examined using four methods of preparation in various combination: (1) mechanical dissociation, (2) enzymatic dissociation, (3) microdissection, and (4) treatment with HCl. Examination of dissected fresh tissue at low magnification confirmed the organization of the gland as an elaborate system of branching ducts ending in clusters of grape-like acini. Mechanical dissociation revealed that: (1) the basal surface of the acinar cells are covered with a fine meshwork of fibrils about 50 nm in diameter. The fibrils always formed a dense reticulum spanning adjacent acinar cells (2) cell surfaces were covered with parallel rows of depressions, each row having a scalloped appearance, (3) individual cells sometimes had a single large furrow, parallel to the rows, giving a polarity to the cell. (4) Acinar cells were punctuated by crater-like depressions, on the order of 1 μm. (5) A large number of small (100 nm) pore-like structures was also a common feature. Following enzymatic dissociation, acinar cells appeared to have suffered considerable trauma. The cell surfaces were covered with a variety of evaginations similar to those seen in freshly dissociated cells observed under Nomarski illumination. Tissue treated with microdissection alone or in concert with 8N HCl revealed other surface features. Capillaries were found in abundance between and partially encircling individual acinar cells. Small axons were often seen accompanying capillaries and other small vessels. However, while capillaries tended to run only in the furrows between adjacent acinar cells, terminal axons separated from the vessels and coursed directly over the basal surface of the individual acinar cells. Terminal axons averaged 1 μm in diameter and were distinctly flattened as compared with capillaries. Axons appeared to end in a cluster of several minute petals. These terminations were always seen on the basal surface of the acinar cells. Structures possibly equivalent to the 'en passant' type of axon termination described by others in light and TEM were observed.