Hypotonic swelling-induced Ca2+ release by an IP3-insensitive Ca2+ store

Hypotonicswelling increases the intracellular Ca²⁺ concentration([Ca²⁺]_i) in vascular smooth muscle cells(VSMC). The source of this Ca²⁺ is not clear. To study thesource of increase in [Ca²⁺]_i in response tohypotonic swelling, we measured [Ca²⁺]_i infura 2-loaded cultured VSMC (A7r5 cells). Hypotonic swelling produced a40.7-nM increase in [Ca²⁺]_i that was notinhibited by EGTA but was inhibited by 1 µM thapsigargin. Priordepletion of inositol 1,4,5-trisphosphate (IP₃)-sensitive Ca²⁺ stores with vasopressin did not inhibit the increasein [Ca²⁺]_i in response to hypotonic swelling.Exposure of ⁴⁵Ca²⁺-loaded intracellular storesto hypotonic swelling in permeabilized VSMC produced an increase in⁴⁵Ca²⁺ efflux, which was inhibited by 1 µMthapsigargin but not by 50 µg/ml heparin, 50 µM ruthenium red, or25 µM thio-NADP. Thus hypotonic swelling of VSMC causes a release ofCa²⁺ from the intracellular stores from a novel sitedistinct from the IP₃-, ryanodine-, and nicotinic acidadenine dinucleotide phosphate-sensitive stores.

     

Effect of Bacteriophage on Colonization of Sugarbeet Roots by Fluorescent Pseudomonas spp

The colonization potential of two fluorescent Pseudomonas strains (M11/4, B2/6) that exhibit antifungal activity in vitro was studied on the roots of sugarbeet plants in a clay loam soil. The cell density of the introduced bacteria declined on the root system over a 16-day test period in nonsterile soil. Strain B2/6 declined at a significantly faster rate compared with M11/4. This loss in viability and difference in colonization ability between M11/4 and B2/6 was not observed in sterile soil. Nutrient deprivation induced by indigenous microorganisms was excluded as a key factor involved in the decline of the introduced bacteria on the basis that strains M11/4 and B2/6 retained viability when subjected to nutrient starvation conditions over a 16-day period. Experiments designed to test whether antagonism by indigenous microorganisms was responsible for the decline in the introduced fluorescent Pseudomonas sp. population revealed the presence of large numbers of bacteriophage in the soil capable of lysing strain B2/6. Reconstitution experiments carried out with sugarbeet seedlings inoculated independently with strains M11/4 and B2/6 and grown in sterile soil to which a soil phage filtrate had been added showed a significant decrease in the viability of strain B2/6 relative to M11/4. Phage antagonistic toward strain B2/6 were detected in 43% of soils taken from the major sugarbeet growing regions of Ireland.     

The cellular and molecular regulation of 1,25(OH)2D3 production

The synthesis of 1,25(OH)₂D₃ is a critical control point in the regulation of calcium metabolism, and possibly in the growth and differentiation of a number of cell types. This paper reviews our current understanding of the regulation of this process at the cellular and molecular levels, with the emphasis on the mechanisms of feedback control 1,25(OH)₂D₃ itself, control of parathyroid hormone, the roles of cyclic AMP dependent protein kinase and protein kinase C, and the interaction between the various intracellular regulators of 1,25(OH)₂D₃ production.     

Chemical composition of whole plant and grain and yield of nutrients in grain of five barley cultivars

Summary twenty seven field experiments were conducted to determine if there were differences between five barley cultivars in their ability to utilize soil nutrients. There were significant differences among cultivars in yield of grain and in concentration of all macro and micro nutrients examined in both the whole plant and grain.Gateway ranked the highest for the concentration of Na, Mn, and Cu in the whole plant and was among the cultivars with highest concentration of Ca, Fe, and Zn. Centennial had generally the lowest concentration of all the nutrients determined in the whole plant. For the concentrations of Na, Mg, and Cu in grain Gateway ranked highest, but ranked third for the concentrations of K, Ca, Fe, Mn, and Zn in grain. Galt had the highest K and Mg concentration and lowest Mn, Cu and Zn concentration in grain. Except for K concentration in grain, Centennial had the lowest concentrations of all other cationic nutrients in grain.Yield of grain rather than nutrient concentration was the most important criteria in determining the ranking of nutrient yields per hectare. Because of its high grain yield, Bonanza produced the largest yield of micronutrient cations and was second to Galt in production of macronutrient cations, although it was lowest in macronutrient cation concentration. Similarly, Bonanza and Galt had the lowest protein concentration, but produced the highest yield of protein per hectare.The implications for animal nutrition of different levels of nutrients between cultivars are discussed.     

An improved purification procedure, an alternative assay and activation of mevalonate kinase by ATP

An improved procedure for the purification of pig liver mevalonate kinase (ATP:mevalonate 5-phosphotransferase, EC 2.7.1.36) is described. A high-voltage electrophoresis assay was developed for mevalonate kinase. The procedure separates mevalonate from phosphomevalonate and also from diphosphomevalonate so that it can be used to measure the subsequent enzyme, phosphomevalonate kinase (EC 2.7.4.2). The assay has allowed the reassessment of the metal ion and nucleotide specificity of the pig liver enzyme. Some of the previously reported properties reflected those of the enzymes in the coupling assay rather than mevalonate kinase itself. A series of compounds were tested as activators or inhibitors of mevalonate kinase. It was found that ATP4-, arsenate and, to a smaller extent, inorganic phosphate activated the enzyme. At fixed MgATP2- (1 mM) concentrations the activation of mevalonate kinase by free ATP4- at pH 8.0 was observed at concentrations at up to 10-fold that of MgATP2- before causing any inhibition. The presence of free ATP4- resulted in a biphasic Lineweaver-Burke plot with apparent Km values for MgATP2- being 0.14 mM and 60 microM, respectively. Fluorescence measurements were consistent with the notion that the binding of excess ATP4- to the enzyme caused a conformational change.     

Effects of lactation on Trichostrongylus colubriformis infections in the guinea pig

Effects of lactation on Trichostrongylus colubriformis infections in the guinea pig. International journal for Parasitology, 4: 177–181. An increase in parasite egg output occurred in lactating guinea pigs infected with Trichostrongylus colubriformis, compared with that of either non-lactating or nulliparous females similarly infected. The lactating animals carried more parasites than either of the other two groups both as fourth stage larvae 9 days after infection and as adults at the peak of egg output 19 days after infection. Both the nulliparous and the non-lactating female guinea pigs had more mast cells and eosinophils in the small intestinal mucosa than did the lactating females.The behaviour of T. colubriformis in the lactating guinea pig is considered to be substantially the same as that of the various nematodes which have been studied in the lactating ewe.