Distribution of concanavalin-A receptor sites on the surface of human resting T lymphocytes. A stereological study using concanavalin-A/colloidal-gold-labelled horseradish peroxidase

Immunolocalisation of PrPSc in scrapie-infected N2a mouse neuroblastoma cells by light and electron microscopy

The causative agent of transmissible spongiform encephalopathies (TSE) is PrPSc, an infectious, misfolded isoform of the cellular prion protein (PrPC). The localisation and trafficking of PrPSc and sites of conversion from PrPC to PrPSc are under debate, particularly since most published work did not discriminate between PrPC and PrPSc. Here we describe the localisation of PrPC and PrPSc in a scrapie-infected neuroblastoma cell line, ScN2a, by light and electron microscopic immunolocalisation. After eliminating PrPC with proteinase K, PrPSc was detected at the plasma membrane, endocytosed via clathrin-coated pits and delivered to early endosomes. Finally, PrPSc was detected in late endosomes/lysosomes. As we detected PrPSc at the cell surface, in early endosomes and in late endosomes/lysosomes, i.e. locations where PrPC is also present, our data imply that the conversion process could take place at the plasma membrane and/or along the endocytic pathway. Finally, we observed the release of PrPC/PrPSc via exocytotic pathways, i.e. via exosomes and as an opaque electron-dense mass which may represent a mechanism of intercellular spreading of infectious prions.

Prenatal exposure to ethanol alters plasma membrane glycoproteins of astrocytes during development in primary culture as revealed by concanavalin A binding and 5'-nucleotidase activity

We have investigated the effect of prenatal exposure to ethanol on the extent of binding and surface distribution of the lectin concanavalin A (con A) on rat cortical astrocytes during the periods of proliferation and differentiation in primary culture. The enzymatic activity of the plasma membrane glycoprotein 5'-nucleotidase was also assessed. The cells were obtained from control fetuses (no exposure to ethanol) and from fetuses prenatally exposed to ethanol. The main findings were: 1) both proliferating and differentiating control astrocytes showed two distinct types of surface con A receptors that could correspond to high- and low-affinity binding sites; 2) the extent of con A binding was greater in mature than in proliferating control cells; 3) the distribution of con A on cell surface components changed with differentiation; 4) the activity of 5'-nucleotidase showed a substantial increment during the period of differentiation; and 5) prenatal exposure to ethanol clearly decreased the ability of astrocytes to bind con A, altered the surface distribution of the receptors for this lectin, and decreased the activity of 5'-nucleotidase. These effects were more marked in proliferating cells. In conclusion, it is shown that the extent of con A labeling and the activity of 5'-nucleotidase in astrocytes are dependent on the stage of cell differentiation and that prenatal exposure to ethanol alters the plasma membrane structure of these cells during development.

Effects of prolonged exposure to ammonia on fluid-phase, receptor-mediated, and adsorptive (non specific) endocytosis in cultured neuroblastoma cells. A flow-cytometry and cytochemical study

The effect of prolonged exposure to ammonia on fluid-phase, receptor-mediated, and adsorptive (non specific) endocytosis in cultured neuroblastoma (Neuro-2a) cells were studied using fluorescein-labeled dextran, concanavalin A conjugated with fluorescein isothiocyanate, and cationized ferritin as tracers. Ammonia treatment increased the rate of endocytosis of cationized ferritin as well as the number of cell elements involved in the process. Moreover, the number of cytoplasmic components containing acid phosphatase activity was also found to increase following ammonia treatment. In contrast, flow-cytometric analyses showed that, under experimental conditions, exposure to ammonia did not alter the intralysosomal pH and had little effect on the fluid-phase and receptor-mediated endocytosis of fluorescein-labeled dextran and concanavalin-A fluorocrome, respectively.

A procedure to measure concanavalin-A binding with atomic spectroscopy and X-ray microanalysis

The purpose of this study was to measure the binding of concanavalin A (conA) in minute regions of tissue by labelling the conA with iron dextran; then by measuring the bound iron per site by a procedure which uses atomic absorption spectrophotometry, X-ray microanalysis, and image analysis. The resulting data for a given region gamma are entered into the formula: (Formula: see text). The resulting quantity "iron at gamma" is directly proportional to conA binding in that region. For this study, three regions of rat renal cortex were compared: distal tubules, collecting ducts and blood vessels; glomeruli; and proximal tubules. Regional iron concentrations were: Combined region (distal tubules, etc.), 0.147 +/- 0.107 microgram/mg tissue; glomeruli, 0.199 +/- 0.087 microgram/mg tissue; and proximal tubules, 1.711 +/- 0.303 microgram/mg tissue.