Biomedical subjects

L F Green

Publications and source records attributed to L F Green.

At least 19 recordsLinked to original sources

PubMed1980

The structure and function of the smooth septate junction in a transporting epithelium: the Malpighian tubules of the New Zealand glow-worm Arachnocampa luminosa.

Junctional complexes between the epithelial cells in the four distinct regions of the glow-worm Malpighian tubule were investigated by electron microscopy using thin sectioning, freeze-fracturing, osmotic disruption and tracer techniques. The lateral plasma membranes of all four cell types are joined by smooth septate junctions but the extent of the complex across the cell depth varies in the four different regions. The width of the septa, the interseptal spacing and the separation between the outer leaflets of the adjacent plasma membranes are different for each cell type. Gap junctions were identified only in the junctional complex between Type IV cells and were intercalated amongst large lateral sinuses. In oblique sections of lanthanum infiltrated tissue, the electron-lucent septa at the basal side of the junction are outlined by the tracer as it penetrates. In the junctional complexes of all four regions the septa appear as short, distinct, linear bars. In tangential sections of gap junctions between Type IV cells, the junctions appear as a hexagonal array of intermembrane particles with a centre to centre spacing of 18 nm. Horseradish peroxidase did not penetrate the junctional complexes very far but readily passed through the basal lamina into the spaces between extracellular invaginations of the basement membrane of the cells. Junctional complexes in all four areas of the tubule have similar freeze-fracture faces. In freeze-fracture replicas of fixed tissue continuous ridges of fused particles are seen on the P face and complementary furrows are found on the E face. Junctional response to osmotically adjusted Ringer solutions was similar in all four cell types. Distortion or 'blistering' of the intercellular space between between the septa of the unction occurred when the tissue was bathed in or injected with a hypertonic Ringer solution. The structure of these junctions, visualized by the different techniques, and the role of the septate junction in a transporting epithelium, are discussed.

Animals↗

PubMed1980

Cryptonephric malpighian tubule system in a dipteran larva, the New Zealand glow-worm, Arachnocampa luminosa (Diptera: Mycetophilidae): a structural study.

The Malpighian tubules of the glow-worm are divided into four morphologically distinct regions, each composed of a different cell type. Part 3 of the Malpighian tubules of A. luminosa is intimately bound to the rectum by a layer of fat body. This association of the tubules with the hindgut is referred to as a cryptonephric system. This type of arrangement has been described in some Coleoptera and the larvae of most Lepidoptera but has never before been reported in the Diptera. In the glow-worm the cryptonephric tubules themselves are small, and adjacent to the fat body the epithelial cells are modified to form very thin windows or 'leptophragmata' (Lison, 1937). The main epithelial cells exhibit features characteristic of highly active, secretory Malpighian tubule cells. The high density of mitochondria and their association with all the microvilli is indicative of a highly active secretory cell. The high concentration of glycogen in these cells and their intimate association with the hindgut suggest that they may, in addition, have a nutrient absorptive function. The role of the cryptonephric rectal complex in the glow-worm is discussed in the light of present knowledge gained from previous studies of coleopteran and larval lepidopteran cryptonephric systems. On structural grounds a model is proposed for the regulation of the ionic environment of the rectum, and the uptake and metabolism of organic material from the rectal lumen by this cryptonephric complex.

Animals↗

PubMed1980

The effect on plasma lipids of the isoenergetic replacement of table sucrose by dried glucose syrup (maize-syrup solids) in the normal diet of adult men over a period of 1 year.

1. Eighteen males (31-62 years) who habitually consumed significant amounts of table sucrose (approximately 25% of total carbohydrate intake) were supplied with their usual intake of sucrose for consumption in conjunction with their normal diet for 1 year, and a record kept of the amount consumed. The sucrose was then replaced isoenergetically by dried glucose syrup (55 D.E.) which contained saccharin to equate the sweetness to that of sucrose. 2. Fasting blood samples were taken every 4 weeks during the 2 years, and the plasma analysed for glucose, cholesterol, triglycerides and phospholipid-P by automated colorimetric methods. Dietary questionnaires were issued every 3 months to confirm the subjects were not substantially altering their diets. 3. In subjects whose weight remained unchanged and in those who lost weight there was a significant fall in cholesterol (P less than 0.025) and phospholipid.P (P less than 0.025) in the glucose-syrup period compared with the sucrose period; triglycerides did not change. In subjects who gained weight there was a significant increase in triglycerides (P less than 0.05), but no change in cholesterol; phospholipid-P fell significantly (P less than 0.0005). 4. The dietary modification in this experiment was sufficiently long to ensure that subjects had adapted, and the results obtained show stable changes in blood lipids which may be attributed to the isoenergetic replacement of table sucrose by glucose syrup.

Adult↗

PubMed1980

Diet, physiological work and accident incidence of forge workers.

Three experiments were made to study the following three factors in forge workers in a hot shop: (a) the metabolic load of daily work, (b) dietary intake, and (c) the effect of supplementing morning dietary intake with glucose syrup ingestion upon accident incidence. High energy output, mean 9.7 MJ (2,300 kcal), complemented high energy intake, mean 15 MJ (3,600 kcal), a shortage of intake in the morning being compensated for after work in the evening. Alcohol intake represented 1 to 2 MJ (240 to 480 kcal) of the evening intake. Glucose syrup ingestion to reverse increased use of fats in the metabolic fuel in the early morning, in a double-blind design, resulted in a significant reduction of accidents. The effect may lie in altered levels of 5-hydroxytryptamine in the central nervous system. Caution in interpreting the effect upon accidents is necessary since the number of subjects was small (57) and the time span limited (18 weeks).

Accidents, Occupational↗

PubMed1979

Regional specialization in the Malpighian tubules of the New Zealand glow-worm Arachnocampa luminosa (Diptera: mycetophilidae). The structure and function of type I and II cells.

The Malpighian tubules of the glow-worm Arachnocampa luminosa are divided into four morphologically distinct regions (Parts 1--4) each comprised of a different cell type (Types I--IV). The ultrastructure of Type II cells is indicative of a transport function. The basal cell surface is highly invaginated and at the apical surface the lumen is lined with microvilli about 80% of which contain mitochondria. Spherites contained in these cells are formed from small vesicles produced by the Golgi apparatus. They have a central uric acid core enclosed by laminations of phosphates of calcium and magnesium. Cells of Part 2 of the tubule secrete a fluid high in potassium (173 mM) and low in sodium (18 mM). The cell is 30 mV negative and the lumen 44 mV positive to the bathing solution. This is consistent with the proposal of an apical cation pump. The secretion produced by Part 2 of the tubules is modified by the Type I cells by the reabsorption of potassium (162 mM) and the addition of sodium (24 mM) to the primary excretory fluid. Type I cells are 20 mV negative and the lumen 22 mV positive with respect to the bathing medium. From ultrastructural observations, Type I cells exhibit features characteristic of transporting cells thought to have an absorptive function. The basal and apical cell surfaces are extensively folded, and mitochondria are found in bands above the basal infoldings and below the microvilli. Mitochondria do not penetrate the microvilli. On comparative grounds, the fine structure of Type I cells suggest that they reabsorb ions from the tubule lumen. Energy for these processes may come from the breakdown of lipids by microperoxisomes contained within these cells. Alternatively, the fluid produced by Part 2 of the tubule may be modified passively by diffusional processes across Type I cells.

Animals↗

PubMed1979