Zero-stress states of arteries

The no-load configuration of a living organ is, in general, not the zero-stress state. The difference can be revealed by cutting up an unloaded organ to such an extent that the stress becomes zero in the tissue everywhere. For the aorta, it is shown that the configuration of the zero-stress state differs considerably from being a cylindrical tube. It is, in fact, an open sector with opening angles varying along the arterial tree. This article presents data on the zero-stress state in the arteries of the rat in normal condition.     

Epitopes that span the tau molecule are shared with paired helical filaments

Tau protein has been shown to be an integral component of Alzheimer paired helical filaments (PHF). However, the extent to which tau is incorporated into PHF has not been clear because the antibodies used to label PHF generally do not have precisely defined epitopes. Here we define the antigenic sites for five monoclonal antibodies that react with tau and cross-react with SDS-extracted neurofibrillary tangles. The reactive sites were determined by screening a lambda gt11 sublibrary expressing small fragments of the tau sequence. The mapped epitopes were found to span almost the entire length of tau, suggesting that PHF contains tau in its entirety or nearly in its entirety. One antibody was found to cross-react with microtubule-associated protein 2, implying some degree of homology between the two proteins.     

A missense mutation (Asp250----Asn) in exon 6 of the human lipoprotein lipase gene causes chylomicronemia in patients of different ancestries.

We have previously reported two common lipoprotein lipase (LPL) gene mutations underlying LPL deficiency in the majority of 37 French Canadians (Monsalve et al., 1990. J. Clin. Invest. 86: 728-734; Ma et al., 1991. N. Engl. J. Med. 324: 1761-1766). By examining the 10 coding exons of the LPL gene in another French Canadian patient, we have identified a third missense mutation that is found in two of the three remaining patients for whom mutations are undefined. This is a G to A transition in exon 6 that results in a substitution of asparagine for aspartic acid at residue 250. Using in vitro site-directed mutagenesis, we have confirmed that this mutation causes a catalytically defective LPL protein. In addition, the Asp250----Asn mutation was also found on the same haplotype in an LPL-deficient patient of Dutch ancestry, suggesting a common origin. This mutation alters a TaqI restriction site in exon 6 and will allow for rapid screening in patients with LPL deficiency.     

Crop uptake and leaching losses of15N labelled fertilizer nitrogen in relation to waterlogging of clay and sandy loam soils

Summary Ammonium nitrate fertilizer, labelled with¹⁵N, was applied in spring to winter wheat growing in undisturbed monoliths of clay and sandy loam soil in lysimeters; the rates of application were respectively 95 and 102 kg N ha⁻¹ in the spring of 1976 and 1975. Crops of winter wheat, oilseed rape, peas and barley grown in the following 5 or 6 years were treated with unlabelled nitrogen fertilizer at rates recommended for maximum yields. During each year of the experiments the lysimeters were divided into treatments which were either freelydrained or subjected to periods of waterlogging. Another labelled nitrogen application was made in 1980 to a separate group of lysimeters with a clay soil and a winter wheat crop to study further the uptake of nitrogen fertilizer in relation to waterlogging. In the first growing season, shoots of the winter wheat at harvest contained 46 and 58% of the fertilizer nitrogen applied to the clay and sandy loam soils respectively. In the following year the crops contained a further 1–2% of the labelled fertilizer, and after 5 and 6 years the total recoveries of labelled fertilizer in the crops were 49 and 62% on the clay and sandy loam soils respectively. In the first winter after the labelled fertilizer was applied, less than 1% of the fertilizer was lost in the drainage water, and only about 2% of the total nitrogen (mainly nitrate) in the drainage water from both soils was derived from the fertilizer. Maximum annual loss occurred the following year but the proportion of tracer nitrogen in drainage was nevertheless smaller. Leaching losses over the 5 and 6 years from the clay and sandy loam soil were respectively 1.3 and 3.9% of the original application. On both soils the percentage of labelled nitrogen to the total crop nitrogen content was greater after a period of winter waterlogging than for freely-drained treatments. This was most marked on the clay soil; evidence points to winter waterlogging promoting denitrification and the consequent loss of soil nitrogen making the crop more dependent on spring fertilizer applications.     

Characterization of non-transferrin-bound iron clearance by rat liver

Recent evidence suggests that the hepatic iron-loading characteristic of hemochromatosis may result in part from efficient hepatic clearance of non-transferrin-bound iron, which is increased in this disorder. However, this hypothesis assumes that hepatic clearance remains highly efficient despite excess iron stores. We therefore studied hepatic uptake of non-transferrin-bound iron in the single-pass perfused rat liver under varying conditions. Animals were iron loaded or depleted by dietary manipulation, but no changes in the efficiency of ferrous iron uptake or the kinetic parameters were seen (single-pass extraction, 59-74%; Km, 16-19 microM; Vmax, 30-32 nmol X min-1 X g liver-1). Added divalent zinc, cobalt, and manganese ions reversibly inhibited ferrous iron uptake and the inhibition by zinc was shown to be competitive. Uptake required calcium, was markedly temperature-sensitive (delta E = 14.3 Kcal/mol), and was relatively insensitive to inhibition of cellular energy metabolism. Particles consistent with ferritin cores were seen in lysosomes of hepatic parenchymal cells within 30 min of perfusion with ferrous iron. These results suggest that ferrous iron is cleared from plasma by a passive, saturable transport process that is not regulated by the iron content of the liver and that may be shared with other transition metal ions. Because clearance is highly efficient, increased levels of non-transferrin-bound iron in plasma may present the liver with an obligatory iron load resulting in progressive accumulation and toxicity.     

Inactivation of alkene oxidation by epoxides in alkene-and alkane-grown bacteria

Summary The oxidation of propene by resting-cells of ethene-grown Mycobacterium E3 was inactivated by 1,2-epoxypropane. Inactivation increased with increasing epoxide concentrations with 50% inactivation at approximately 30 mM epoxide. Other lower epoxides as epoxyethane and 1,2-epoxybutane also inactivated oxidation of propene as well as of other alkenes. Propene oxidation by resting-cells of ethane-grown Mycobacterium E20 and resting-cells of methane-grown Methylosinus trichosporium OB3b was inactivated for 50% at much lower 1,2-epoxypropane concentrations of approximately 1 and 3 mM respectively. It was demonstrated that in vivo the predominant effect of 1,2-epoxypropane was on the epoxidizing enzyme, i.e. alkene mono-oxygenase (strain E3), alkane mono-oxygenase (strain E20) and methane mono-oxygenase (methylotroph) and that the effect of the epoxide on the alkene mono-oxygenase was irreversible.     

Structural and functional analysis of the respiratory burst in the phagocytosing macrophage

The interrelation between structural changes and oxygen consumption by the phagocyting macrophage was studied. The mean number of phagocyted particles was estimated by the method of stereological transformation. It is found that the uptake of yeast particles and CN- -nonsensitive oxygen consumption is related to the concentration of yeast cells in the incubation medium. A positive correlation was established between the oxygen consumption and the mean number of phagocyted particles. The results obtained may suggest that the "respiration burst" takes place in the contact area of the macrophage and the phagocyted material, and its extent probably depends on the surface of that contact area.     

A modified method of UDS detection in vitro suitable for screening the DNA-damaging effects of chemicals

The UDS induced in cultured FL cells by exposure to chemicals was measured as hydroxyurea-resistant incorporation of 3H-TdR in the acid-insoluble fraction of the 14C-TdR-prelabelled cells synchronized by the combination of arginine starvation and pretreatment with hydroxyurea. The level of UDS is represented by the ratios of 3H/14C radioactivities which are measures of specific activities of 3H. Two direct-acting alkylating agents, MMS and MNNG, a cross-linking agent, mitomycin C, and 3 procarcinogens, B(a)P, AFB1 and cyclophosphamide elicited UDS in the absence or presence of the liver-metabolizing system. Three chemicals of unknown carcinogenicity were also able to induce UDS in this assay system, i.e., bis-(O,O-diethylphosphinothioyl)-disulphide, 4-chlorophenoxy acetic acid (sodium salt) and caramelized malt sugar. With the exception of 4-chlorophenoxy acetic acid, they were also active in the Ames test.     

Calcium reduces the sodium permeability of luminal membrane vesicles from toad bladder. Studies using a fast-reaction apparatus

Regulation of the sodium permeability of the luminal membrane is the major mechanism by which the net rate of sodium transport across tight epithelia is varied. Previous evidence has suggested that the permeability of the luminal membrane might be regulated by changes in intracellular sodium or calcium activities. To test this directly, we isolated a fraction of the plasma membrane from the toad urinary bladder, which contains a fast, amiloride-sensitive sodium flux with characteristics similar to those of the native luminal membrane. Using a flow-quench apparatus to measure the initial rate of sodium efflux from these vesicles in the millisecond time range, we have demonstrated that the isotope exchange permeability of these vesicles is very sensitive to calcium. Calcium reduces the sodium permeability, and the half-maximal inhibitory concentration is 0.5 microM, well within the range of calcium activity found in cells. Also, the permeability of the luminal membrane vesicles is little affected by the ambient sodium concentration. These results, when taken together with studies on whole tissue, suggest that cell calcium may be an important regulator of transepithelial sodium transport by its effect on luminal sodium permeability. The effect of cell sodium on permeability may be mediated by calcium rather than by sodium itself.