The Na+-independentd-glucose transporter in the enterocyte basolateral membrane: Orientation and cytochalasin B binding characteristics

Summary Phloridzin-insensitive, Na⁺-independentd-glucose uptake into isolated small intestinal epithelial cells was shown to be only partially inhibited by trypsin treatment (maximum 20%). In contrast, chymotrypsin almost completely abolished hexose transport. Basolateral membrane vesicles prepared from rat small intestine by a Percoll^® gradient procedure showed almost identical susceptibility to treatment by these proteolytic enzymes, indicating that the vesicles are predominantly oriented outside-out. These vesicles with a known orientation were employed to investigate the kinetics of transport in both directions across the membrane. Uptake data (i.e. movement into the cell) showed aK _t of 48mm and aV _max of 1.14 nmol glucose/mg membrane protein/sec. Efflux data (exit from the cell) showed a lowerK _t of 23mm and aV _max of 0.20 nmol glucose/mg protein/sec.d-glucose uptake into these vesicles was found to be sodium independent and could be inhibited by cytochalasin B. TheK _t for cytochalasin B as an inhibitor of glucose transport was 0.11 m and theK _D for binding to the carrier was 0.08 m.d-glucose-sensitive binding of cytochalasin B to the membrane preparation was maximized withl- andd-glucose concentrations of 1.25m. Scatchard plots of the binding data indicated that these membranes have a binding site density of 8.3 pmol/mg membrane protein. These results indicate that the Na⁺-independent glucose transporter in the intestinal basolateral membrane is functionally and chemically asymmetric. There is an outward-facing chymotrypsin-sensitive site, and theK _t for efflux from the cell is smaller than that for entry. These characteristics would tend to favor movement of glucose from the cell towards the bloodstream.     

Enzymic Synthesis of Leukotriene B4 in Guinea Pig Brain

Leukotriene B4 [5(S), 12(R)-dihydroxy-6, 14-cis-8,10-trans-eicosatetraenoic acid] was obtained from endogenous arachidonic acid when slices of the guinea pig brain cortex were incubated with the calcium ionophore A 23187. Enzymes involved in its synthesis, arachidonate 5-lipoxygenase [arachidonic acid to 5(S)-hydroperoxy-6-trans-8,11,14-cis-eicosatetraenoic acid and subsequently to leukotriene A4] and leukotriene A4 hydrolase (leukotriene A4 to B4), were present in the cytosol fraction. Arachidonate 5-lipoxygenase was Ca2+-dependent, and was stimulated by ATP and the microsomal membrane, as was noted for the enzyme from mast cells. The lipid hydroperoxides stimulated 5-lipoxygenase by four- to sixfold. The leukotriene A4 hydrolase activity was rich in brain, and the specific activity (0.4 nmol/min/mg of protein) was much the same as that of guinea pig leukocytes. High activities of these enzymes were detected in the olfactory bulb, pituitary gland, hypothalamus, and cerebral cortex. Since leukotriene B4 is enzymically synthesized in the brain, possible roles related to neuronal functions or dysfunctions deserve to be examined.     

Polymorphism of the vitamin D binding protein (DBP) among primates: an evolutionary analysis

The distribution of the DBP (vitamin D binding protein) polymorphism is now well characterized among human populations but for primates only limited results are known. The aim of this paper is to describe the electrophoretic polymorphism of this protein among various species. Using three different electrophoretic methods, we are able to detect an unknown polymorphism and to classify the different alleles observed. These results may be used to set an international nomenclature for further comparisons. The different electrophoretic mobilities between Old and New World Monkeys show that: 1) the Cercopithecoïdea are presenting the largest genetic heterogeneity; 2) the DBP among the Galago corresponds to the lowest isoelectric points observed among Primates; 3) during the evolution from nonhuman Primates to Man, the DBP is able to keep its affinity for vitamin D derivatives despite the occurrence of significant molecular modifications; 4) among Anthropoïdea, the electrophoretic patterns of DBP are very close to the human Gc 1 proteins. These results show that evolution at the DBP level can be considered as a continous mechanism of structural modifications. A significant transition occurs during the differentiation between Cercopithecoïdea and Anthropoïdea. It is not too speculative to consider that some electrophoretic forms detected among Gorilla, Pongo, or Pan may be identical to rare variants observed among humans.     

Phyletic and evolutionary relationships ofBrachyscome lineariloba (Compositae)

A comparison of karyotypes ofBrachyscome breviscapis (2n = 8),B. lineariloba cytodemes E (2n = 10), B (2n = 12) and C (2n = 16) suggests that these species have a homoelogous basic set of four chromosome pairs, two large pairs and two small, and that theB. lineariloba cytodemes E, B and C are related toB. breviscapis by successive additions of small chromosomes. A pronounced asynchrony of chromosome condensation between these large and small chromosomes has been observed. In the artificial hybrids betweenB. dichromosomatica (2n = 4) ×B. breviscapis, and theB. lineariloba cytodemes, theB. dichromosomatica chromosomes are similar in size and condensation behaviour to the small chromosomes ofB. breviscapis and ofB. lineariloba cytodemes E, B and C. Meiotic pairing in these hybrids also demonstrates the strong affinities between these chromosomes. It is suggested thatB. breviscapis may be of amphidiploid origin between a species with two large early condensing chromosome pairs and another,B. dichromosomatica-like species with two small late condensing pairs. It seems most likely that the additional small and late condensing chromosomes inB. lineariloba cytodemes E, B and C are derived from theB. dichromosomatica-like parent, and that each addition increases vigour, fecundity and drought tolerance, allowing these cytodemes to colonize more open and arid environments. Transmission of the univalents in the quasidiploidB. lineariloba cytodeme E was verified as being via the pollen, and not via the embryo sacs.The cytology ofBrachyscome lineariloba (Compositae, Asteroidae), 10.     

山药化学成分的研究

从胡椒科植物山蒟中分得两个新木脂素类成分(Ia)和(Ⅱ),以及巴豆环氧素(Crorepoxide)(Ⅲ)和β-谷甾醇(Ⅳ)。经光谱分析及化学鉴定,(Ia)、(Ⅱ)为新结构,分别命名为山蒟素 B(hancinone)、山蒟素 C(hancinone C)。     

Major histocompatibility (B) complex and sex effects on the phytohaemagglutinin wattle response

The influence of the major histocompatibility (B) complex and sex on the phytohaemagglutinin (PHA) wattle response was studied in 136 segregants (B2/B2, B2/B5 and B5/B5) of a fourth generation cross between inbred lines 6(1) and 15(1). At 6 weeks of age, chickens were injected with 100 micrograms purified PHA-P. Wattle thickness measurements were taken 4, 24, 48, 72 and 96 h after injection. Analysis of variance showed that 4 h after injection, males had a significantly higher response than females but the sex-genotype interaction was also significant. Females had higher responses than males 24 and 48 h after injection as a consequence of more rapid development and earlier resolution of the reaction in males. B2/B2 chickens had significantly lower responses than B5/B5 chickens 72 and 96 h after injection, signifying a faster late resolution phase in the B2/B2 genotype. The developmental and early resolution phases of the PHA wattle response were influenced by sex while the late resolution phase was influenced by B genotype.     

Stellate cells storing retinol in the liver of adult lamprey,Lampetra japonica

Summary Distribution, localization and fine structure of the stellate cells in the liver of lamprey, Lampetra japonica, were studied during the spawning migration by use of Kupffer's gold-chloride method, fluorescence microscopy for vitamin A (retinol) and electron microscopy. The stellate cells in the lamprey liver differ in some of their properties from those in mammalian livers. Stellate cells which store abundant retinol in lipid droplets, occur not only in the hepatic parenchyma, but also in the dense perivascular and capsular connective tissue of the liver and in the interstitium of pancreatic tissue. In the hepatic parenchyma these cells are located perisinusoidally or along thick bundles of collagen fibrils. The stellate cells display a number of large retinol-containing lipid droplets, granular endoplasmic reticulum, tubular structures, dense bodies, Golgi complex, microtubules, and microfilaments. In the space of Disse, the stellate cells and extracellular fibrilar components such as collagen fibrils and microfibrils (11–12 nm in diameter) are intervened between the two layers of basal laminae. Differentiation and possible functions of the stellate cells in the lamprey liver are discussed.     

In vivo binding and uptake of low-density lipoprotein-gold- and albumin-gold conjugates by parenchymal and sinusoidal cells of the fetal rat liver

Summary To elucidate the participation of fetal rat liver cells in the receptor-mediated internalization of low-density lipoproteins (LDL), rat fetuses were injected with either LDL-gold or albumin-gold conjugates. The degree of binding and uptake of LDL-gold and albumin-gold by parenchymal and sinusoidal cells of the fetal rat liver differs markedly. Endothelial cells exhibit low LDL-gold uptake. In contrast, parenchymal cells internalize LDL-gold more actively (45 ± 8 LDL conjugates/100 m² cytoplasm within 60 min). Kupffer cells exceed this value by a factor of 20. The uptake of albumin-gold by endothelial and Kupffer cells is high, whereas it is extremely low in parenchymal cells. Estradiol pretreatment causes a significant doubling (p<0.05) of the LDL-gold particle density/100 m² cytoplasm both in parenchymal and Kupffer cells, whereas estradiol has no effect on the albumin uptake. The results strongly indicate that LDL uptake by parenchymal and Kupffer cells in the fetal rat liver is mediated by estrogen-inducible receptors, which may correspond to B, E receptors in the adult liver.