The localization of acid phosphatase in rat liver cells as revealed by combined cytochemical staining and electron microscopy.

Discrete localization of stain in pericanalicular granules was found in 10 micro frozen sections of formol-phosphate-sucrose-fixed liver stained by the Gomori acid phosphatase technique and examined in the light microscope. The staining patterns, before and after treatment with Triton X-100 and lecithinase, were identical with those previously reported for formol-calcium-fixed material treated in the same way, and it can be assumed that the stained granules are identical with "lysosomes." Examination in the light microscope of the staining patterns and lead penetration in fixed blocks and slices of various dimensions showed nuclear staining and other artefacts to be present, produced by the different rates of penetration of the various components of the staining medium into the tissue. A uniform pericanalicular staining pattern could be obtained, however, with slices not more than 50 micro thick, into which the staining medium could penetrate rapidly from both faces. The staining pattern produced in 50 micro slices was the same both at pH 5.0 and pH 6.2, and was not altered by subsequent embedding of the stained material in butyl methacrylate. Electron microscopy showed the fine structure of fixed 50 micro frozen slices to be well preserved, but it deteriorated badly when they were incubated in the normal Gomori medium at pH 5.0 before postfixing in osmium tetroxide. After incubation in the Gomori medium at pH 6.2, the detailed morphology was substantially maintained. In both cases lead phosphate, the reaction product, was found in the pericanalicular regions of the cell, but only in the vacuolated dense bodies and never in the microbodies. Not every vacuolated dense body contained lead, and stained and unstained bodies were sometimes seen adjacent to each other. This heterogeneous distribution of stain within a morphologically homogeneous group of particles is consistent with de Duve's suggestion (9) that there is a heterogeneous distribution of enzymes within the lysosome population. It is concluded from these investigations that the vacuolated dense bodies seen in the electron microscope are the morphological counterparts of the "lysosomes" defined biochemically by de Duve.