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The electron-microscopical autoradiographical resolution of a gold latensification-elon ascorbic acid (GEA) developer for Ilford L4 emulsion was determined experimentally, using radioactive line sources of tritiated albumin (Heijnen and Geuze, 1977). For sections with a thickness of 62 nm (SD +/- 11), which were covered with a carbon layer about 5 nm thick and a slightly overlapping monolayer of L4 silver bromide crystals, the measured half-distance (HD) of resolution was 115 nm. This improvement in resolution, the high efficiency of the GEA developer for L4 emulsion (Wisse and Tates, 1968), and the excellent visibility of the cellular structures under the small silver grains, mean that the L4-GEA combination deserves preverence as a method for quantitative electron-microscopical autoradiography.

The effect of colchicine on the intracellular transport of 3H-fucose-labelled glycoproteins in the absorptive cells of cultured biopsy specimens of the human intestine was investigated by light- and electron-microscopical autoradiography and by biochemical methods. The results showed a decrease in the radioactivity of the cell coat on the microvilli and an increase in the Golgi apparatus and in the apical vesicles and tubules. This divergence is attributed to a colchicine-induced impairment of the normal transport of cell-coat glycoproteins from the Golgi apparatus, via the apical vesicles and tubules, to the apex of the cell. The radioactivity of the lysosome-like bodies in the absorptive cells cultured with colchicine also increased. This finding supports a crinophagic function of these organelles in the degradation of excess cell-coat material.

After stimulation of the mouse peritoneal cavity with newborn calf serum (NBCS), four types of monocyte and macrophage were distinguished on the basis of peroxidase (PO) patterns. Cytochemically, these cells showed strong heterogeneity in 5'-nucleotidase (5'N) activity. Monocytes and monocyte-derived macrophages with PO activity in granules lacked 5'N activity. Resident macrophages (with PO activity in RER and nuclear envelope) generally had significant 5'N activity on the plasma membrane, the pattern showing close correlation with the biochemical findings. The group of PO-negative macrophages comprised both 5'N-negative and 5'N-positive cells. These findings suggest two possibilities, i.e., that monocytes (5'N-)transform via PO-negative cells (5'N -/+) into resident macrophages (5'N +), or that the monocytes and monocyte-derived macrophages and the resident macrophages represent separate lineages. The fourth type of macrophage, the exudate-resident cell (with PO activity both in granules and in the RER and nuclear envelope), occurred only in low numbers and very late after NBCS stimulation, and is therefore considered not to be a transitional cell between monocytes and resident macrophages.

The transport of 3H-fucose- and 3H-glucosamine-labelled glycoproteins in the absorptive cells of cultured human small-intestinal tissue was investigated with light- and electron-microscopical autoradiography. The findings showed that these glycoproteins were completed in the Golgi apparatus and transported in small vesicular structures to the apical cytoplasm of these cells. Since this material arrived in the cell coat on the microvilli and in the lysosome-like bodies simultaneously, a crinophagic function of these organelles in the regulation of the transport or secretion of cell-coat material was supported. In the absorptive cells of patients with fucosidosis or Hunter's type of lysosomal storage disease, a smiliar transport of cell-coat material to the lysosome-like bodies and a congenital defect of a lysosomal hydrolase normally involved in the degradation of cell-coat material, can explain the accumulation of this material in the dense bodies.

A method was developed for the demonstration of 5'-nucleotidase in murine peritoneal resident macrophages. The cells are incubated cytochemically without agitation and cerium chloride is used as a trapping agent. Under these conditions, the great majority of the macrophages in the unstimulated peritoneal cavity show enzyme activity in the plasma membrane. In the presence of AMP-S (an AMP analogue inhibiting 5'-nucleotidase, as shown biochemically) there was a decrease in both the number of positive macrophages and the amount of reaction product on the plasma membranes. This indicates that the enzyme activity detected by our cytochemical procedure is attributable to 5'-nucleotidase.