The surface distribution of low density lipoprotein receptors on cultured fibroblasts and endothelial cells. Ultrastructural evidence for dispersed receptors

The distribution of low density lipoprotein (LDL) receptors marked with colloidal gold-conjugated low density lipoproteins has been mapped on the surfaces of cultured human skin fibroblasts and bovine aortic endothelial cells viewed whole in the transmission electron microscope. A dispersed or scattered population of LDL receptors, in addition to and clearly distinct from clustered receptors was detected on the surfaces of both fibroblasts and dividing endothelial cells. No LDL receptors could be detected on contact-inhibited endothelial cells. Clustered receptors imaged in whole-mount preparations were often arranged in rings with an approximate diameter of 250 nm. In ultra-thin sections of marked cells, clustered receptors were localised in coated pits while the few dispersed receptors seen were restricted to non-coated membrane regions. Clustered receptors often appeared localised on the rims of coated pits whose central areas were not marked. The dispersed population of receptors was usually distributed diffusely amongst the clusters on dividing endothelial cells and normal fibroblasts. Only the dispersed population appeared on LDL receptor internalisation-defective mutant fibroblasts. The marginal zones of both fibroblasts and dividing endothelial cells were populated by dispersed receptors. Clusters appeared further "inland" and were rarely seen near the cell margins. These results indicate that LDL receptors on dividing endothelial cells and fibroblasts may be dispersed on the cell surface upon or soon after their insertion during recycling.     

Immunohistochemical localization of S-100 protein, glial fibrillary acidic protein, and neuron-specific enolase in the pars distalis of quail, rat, and human hypophyses

In the present study, we have localized immunohistochemically S-100 protein, glial fibrillary acidic (GFA) protein, and neuron-specific enolase (NSE) by the unlabelled antibody peroxidase-antiperoxidase technique. Special attention was paid to the influence of fixation and of pretreatment of sections with proteolytic enzymes. It appeared that the final immunostaining of a given antigen largely depends on the fixative and on the species used. Moreover, pepsin pretreatment proved to be necessary to unmask S-100 protein in quail and GFA protein in rat. S-100 protein (rat, human) and GFA protein (human) immunoreactivities were detected in the folliculo-stellate (FS) cells. In quail, S-100 protein was also found in cells, which were not arranged around a follicular lumen and, in rat, the endothelial cells were immunostained for GFA protein. Clusters of granular cells were weakly immunostained for NSE in all species. An exclusive relationship between FS cells and S-100 protein could not be ascertained from this study.     

Operant supplementary heating in groups of growing pigs in relation to air velocity

The aim of the experiments was to investigate the effect of air velocity on the temperature preferred by growing pigs 12–14 weeks old. Pigs displayed a temperature preference by means of operant supplemental heating. They pushed a button connected to heating lamps. Six experiments of three weeks each and with two treatments with a group of 8 pigs each were made. Animals were housed in groups and weighed 14–20 kg at the start of the experiments. Air velocity was 0.08, 0.25 and 0.40 m/s. At each air velocity four replicates were made. Mean temperatures preferred were 17.9°C at 0.08 m/s, 20.5°C at 0.25 m/s and 21.7°C at 0.40 m/s. Within a day temperature preference fluctuated with 5.7 K at 0.08 m/s, 4.3 K at 0.25 m/s and 4.2 K at 0.4 m/s. Temperatures preferred were highest during day time.     

Changes in the acinar distribution of some enzymes involved in carbohydrate metabolism in rat liver parenchyma after experimentally induced cholestasis

Extrahepatic cholestasis induced by ligation and transsection of the common bile duct caused a change in the parenchyma/stroma relationship in rat liver. Two weeks after ligation, the periportal zones of the parenchyma were progressively invaded by expanding bile ductules with surrounding connective tissue diverging from the portal areas. Parenchymal disarray developed and small clumps of hepatocytes or isolated hepatocytes were scattered within the expanded portal areas. These cells showed normal activity of lactate, succinate and glutamate dehydrogenase and may, therefore, be considered to be functionally active. After cholestasis the remainder of the liver parenchyma showed adaptational changes with respect to glucose homeostasis, as demonstrated by histochemical means. Glycogen stores disappeared completely whereas glycogen phosphorylase activity increased about ten fold. The increased glycogen phosphorylase activity and glycogen depletion indicate a greater glycogenolytic capacity in liver parenchyma after bile duct ligation to maintain as far as possible a normal plasma glucose concentration. The parenchymal distribution pattern of glucose-6-phosphatase activity did not change significantly after bile duct ligation. The isolated hepatocytes within the expanded portal tracts showed a high activity of this enzyme whereas the pericentral parenchyma was only moderately active. The distribution patterns of glucose-6-phosphate dehydrogenase and lactate dehydrogenase activity in the liver parenchyma were also largely unchanged after bile duct ligation, but the histochemical reaction for glucose-6-phosphate dehydrogenase activity demonstrated infiltration of the remainder of the parenchyma by non-parenchymal cells, possibly Küpffer cells and leucocytes as part of an inflammatory reaction. Under normal conditions the mitochondrial enzymes succinate and glutamate dehydrogenase show an opposite heterogenous distribution pattern in liver parenchyma. Following cholestasis both enzymes became uniformly distributed. The underlying regulatory mechanism for these different changes in distribution patterns of enzyme activities is not yet understood.     

No evidence for a pleiotropic relationship between male sterility and cyanide-resistant respiration in Plantago lanceolata

Gynodioecy, the coexistence of hermaphrodites and male steriles, is frequent in populations of Plantago lanceolata L. A condition for the maintenance of gynodioecy in an obligatory outbreeding species like this is an increase in female fitness in male steriles compared with hermaphrodites. One of the possible underlying mechanisms, a lower cyanide-resistant respiration in male steriles, which could lead to a higher metabolic efficiency, was investigated. For the experiments adult plants were used, because the effects which compensate for male sterility have been found in characters like seed production and longevity. No general correlation between sex phenotype and cyanide-resistant respiration capacity, or with any other respiration component, was found. Only in a single cross a strong correlation between cyanide-resistant respiration activity and sex phenotype was established, male steriles possessing the higher activity. The conclusion from these experiments is that there is no pleiotropic relationship between respiration levels and sex phenotype. The strongly significant correlation mentioned is ascribed to chromosomal linkage.     

Maintenance of low cl concentrations in mesophyll cells of leaf blades of barley seedlings exposed to salt stress

The concentrations of vacuolar Na⁺ and Cl⁻ in the epidermal and mesophyll cells of the leaf blade and sheath of Hordeum vulgare seedlings (cv California Mariout and Clipper) were measured by means of quantitative electron probe x-ray microanalysis. A preferential accumulation of Cl⁻ in vacuoles of epidermal cells in both blade and sheath and a low level in mesophyll cells of the blade were evident in plants grown in full strength Johnson solution. The concentration of Cl⁻ in the mesophyll cells of the blade remained at a low level after exposure to 50 or 100 millimolar NaCl for 1 day or to 50 millimolar for 4 days, while at the same time the concentration of Cl⁻ in the epidermis and mesophyll of the sheath showed a dramatic increase. Clipper generally contained more Cl⁻ in the mesophyll cells of the blade than California Mariout. A greater accumulation of Na⁺ in the mesophyll of the sheath relative to that of the blade was only apparent after treatment with 100 millimolar NaCl for 1 day or 50 millimolar for 4 days. These results confirm the suggestion that sheath tissue is capable of accumulating excess Cl⁻ (and to a lesser extent Na⁺) and suggest that the site of regulation of Cl⁻ concentration in the barley leaf is located in the mesophyll cells of the blade.     

Fructose 2,6-bisphosphate hydrolyzing enzymes in higher plants

The phosphatases that hydrolyze fructose 2,6-bisphosphate in a crude spinach (Spinacia oleracea L.) leaf extract were separated by chromatography on blue Sepharose, into three fractions, referred to as phosphatases I, II, and III, which were further purified by various means. Phosphatase I hydrolyzed fructose 2,6-bisphosphate, with a K_m value of 30 micromolar, to a mixture of fructose 2-phosphate (90%) and fructose 6-phosphate (10%). It acted on a wide range of substrates and had a maximal activity at acidic pH. Phosphatase II specifically recognized the osyl-link of phosphoric derivatives and had more affinity for the β-anomeric form. Its apparent K_m for fructose 2,6-bisphosphate was 30 micromolar. It most likely corresponded to the fructose-2,6-bisphosphatase described by F. D. Macdonald, Q. Chou, and B. B. Buchanan ([1987] Plant Physiol 85: 13-16). Phosphatase III copurified with phosphofructokinase 2 and corresponded to the specific, low-K_m (24 nanomolar) fructose-2,6-bisphosphatase purified and characterized by Y. Larondelle, E. Mertens, E. Van Schaftingen, and H. G. Hers ([1986] Eur J Biochem 161: 351-357). Three similar types of phosphatases were present in a crude extract of Jerusalem artichoke (Helianthus tuberosus) tuber. The concentration of fructose 2,6-bisphosphate decreased at a maximal rate of 30 picomoles per minute and per gram of fresh tissue in slices of Jerusalem artichoke tuber, upon incubation in 50 millimolar mannose. This rate could be accounted for by the maximal extractable activity of the low-K_m fructose-2,6-bisphosphatase. A new enzymic method for the synthesis of β-glucose 1,6-bisphosphate from β-glucose 1-phosphate and ATP is described.