Electron microscope observations on the carbohydrate-rich cell coat present at the surface of cells in the rat.
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Periodic acid-silver methenamine, a fairly specific technique for glycoprotein detection, was used to stain a variety of rat tissues, in the hope of confirming the existence of a carbohydrate-rich "cell coat" at the surface of mammalian cells. It was found that nearly all cells are coated by a thin layer of stained material. Around fibrocytes and migrating blood cells, the layer is uniform and merges with the ground substance. In the nervous system, cells and processes are surrounded with a layer whose density increases in synaptic clefts. Around epithelial cells, the layer outlines apical microvilli, follows lateral interspaces, and extends between cells and basement membrane. The layer is continuous with the middle plate of desmosomes and can be followed within the wide portion of terminal bars. In contrast, staining usually vanishes when two adjacent plasma membranes fuse to form tight junctions. These findings indicate that the stained layer is a "cell coat" located outside the plasma membrane. Since the cell coat is also stained by colloidal thorium, a technique for detection of acidic carbohydrates, this structure presumably contains not only glycoprotein(s) but also acidic residues. The carbohydrates may play a role in holding cells together and in controlling the interactions between cells and environment. (+info)
Orbital forcing of the marine isotope stage 9 interglacial.
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Milankovitch orbital forcing theory has been used to assign time scales to many paleoclimate records. However, the validity of this theory remains uncertain, and independent sea-level chronologies used to test its applicability have been restricted largely to the past approximately 135,000 years. Here, we report U-series ages for coral reefs formed on Henderson Island during sea-level high-stands occurring at approximately 630,000 and approximately 330,000 years ago. These data are consistent with the hypothesis that interglacial climates are forced by Northern Hemisphere summer solar insolation centered at 65 degrees N latitude, as predicted by Milankovitch theory. (+info)
New ages for the last Australian megafauna: continent-wide extinction about 46,000 years ago.
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All Australian land mammals, reptiles, and birds weighing more than 100 kilograms, and six of the seven genera with a body mass of 45 to 100 kilograms, perished in the late Quaternary. The timing and causes of these extinctions remain uncertain. We report burial ages for megafauna from 28 sites and infer extinction across the continent around 46,400 years ago (95% confidence interval, 51,200 to 39,800 years ago). Our results rule out extreme aridity at the Last Glacial Maximum as the cause of extinction, but not other climatic impacts; a "blitzkrieg" model of human-induced extinction; or an extended period of anthropogenic ecosystem disruption. (+info)
Direct determination of the timing of sea level change during termination II.
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An outcrop within the last interglacial terrace on Barbados contains corals that grew during the penultimate deglaciation, or Termination II. We used combined 230Th and 231Pa dating to determine that they grew 135.8 +/- 0.8 thousand years ago, indicating that sea level was 18 +/- 3 meters below present sea level at the time. This suggests that sea level had risen to within 20% of its peak last-interglacial value by 136 thousand years ago, in conflict with Milankovitch theory predictions. Orbital forcing may have played a role in the deglaciation, as may have isostatic adjustments due to large ice sheets. Other corals in the same outcrop grew during oxygen isotope (delta18O) substage 6e, indicating that sea level was 38 +/- 5 meters below present sea level, about 168.0 thousand years ago. When compared to the delta18O signal in the benthic V19-30/V19-28 record at that time, the coral data extend to the previous glacial cycle the conclusion that deep-water temperatures were colder during glacial periods. (+info)
Delays in insulin signaling towards glucose disposal in human skeletal muscle.
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We explored whether the delay that occurs between a rise in plasma insulin and the increase of glucose disposal occurs before, at, or downstream of steps that are believed to be part of the insulin signaling cascade. Skeletal muscle biopsies were obtained from 16 nondiabetic subjects before, and 20 and 180 min after plasma insulin levels had been augmented in euglycemic hyperinsulinemic glucose clamps. Although plasma insulin had reached 98% of its final concentration within 10 min, insulin receptor kinase (IRK) activity, p85 associated with insulin receptor substrate-1 (IRS-1), IRS-1-associated phosphatidylinositol 3-kinase (PI3K) activity, and Thr(308)-protein kinase B (PKB) phosphorylation in the muscle biopsies at 20 min had reached only 60, 48, 34 and 47% respectively of those at 180 min. This suggests a delay before the level of IRK and little or no delay between IRK and PKB activation. The observation that glycogen synthase activity and glucose disposal at 20 min had both only reached 25% of the respective values at 180 min suggests an additional delay downstream of the investigated signaling steps. (+info)
Environmental radionuclides in surface soils of Vietnam.
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A database on 238U, 232Th, 40K, and 137Cs in surface soils was established to provide inputs for the assessment of the collective dose to the population of Vietnam and to support soil erosion studies using 137Cs as a tracer. A total of 292 soil samples was taken from undisturbed sites across the territory and the concentrations of radionuclides were determined by gamma spectrometry method. The multiple regression of 137Cs inventories against characteristics of sampling locations allowed us to establish the distribution of 137Cs deposition density and its relationship with latitude and annual rainfall. The 137Cs deposition density increases northward and varies from 178 Bq m(-2) to 1,920 Bq m(-2). High rainfall areas in the northern and central parts of the country have received considerable 137Cs inputs exceeding 600 Bq m-2, which is the maximum value that can be expected for Vietnam from the UNSCEAR global pattern. The mean activity concentrations of naturally occurring radionuclides 238U, 232Th, and 40K are 45, 59, and 401 Bq kg(-1), respectively, which entail an average absorbed dose rate in air of 62 nGy h(-1), which is about 7% higher than the world average. (+info)
A 20-year follow-up study on the effects of long-term exposure to thorium dust.
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OBJECTIVE: To investigate the possible effects of long-term exposure to dust containing thorium and thoron progeny on dust-exposed miners. METHODS: A negative, high voltage, exhaled thoron progeny measurement system was used to estimate the miners' thorium lung burden. RESULTS: The highest thorium lung burden of 638 miners was 11.11 Bq. The incidence of stage 0(+) pneumoconiosis was higher among dust-exposed miners. Lung cancer mortality of the dust-exposed miners was significantly higher than that of controls (P < 0.005). CONCLUSION: There is a difference in cancer rates between those who have long-term exposure to dust containing thorium (in which carcinogenic ThO(2) and SiO(2) exist) and thoron progeny and those who have not. (+info)
Thorium-232 exposure during tungsten inert gas arc welding and electrode sharpening.
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To assess the exposure of welders to thorium-232 (232Th) during tungsten inert gas arc (TIG) welding, airborne concentrations of 232Th in the breathing zone of the welder and background levels were measured. The radioactive concentrations were 1.11 x 10(-2) Bq/m3 during TIG welding of aluminum (TIG/Al), 1.78 x 10(-4) Bq/m3 during TIG welding of stainless steel (TIG/SS), and 1.93 x 10(-1) Bq/m3 during electrode sharpening, with 5.82 x 10(-5) Bq/m3 background concentration. Although the annual intake of 232Th estimated using these values did not exceed the annual limit intake (ALI, 1.6 x 10(2) Bq), we recommend reducing 232Th exposure by substituting thoriated electrodes with a thorium-free electrodes, setting up local ventilation systems, and by using respiratory protective equipment. It is also necessary to inform workers that thoriated tungsten electrodes contain radioactive material. (+info)