Investigation of 1,3-dipolar cycloaddition reactions of unsaturated nitrones in ionic liquids

The effect of the media (achiral and chiral ionic liquids) on the stereochemistry of intramolecular 1,3-dipolar cycloaddition reactions of D-galactose-derived omega-unsaturated nitrones, leading to bicyclic isoxazolidines, has been investigated.     

Myofilament sensitivity to Ca2+ in ventricular myocytes from the Goto–Kakizaki diabetic rat

The chronic effects of type 2 diabetes mellitus on myofilament sensitivity to Ca(2+) in ventricular myocytes from the Goto-Kakizaki (GK) rat have been investigated. Experiments were performed in ventricular myocytes isolated from 17-month GK rats and age-matched Wistar controls. Myocytes were loaded with fura-2 (an indicator for intracellular Ca(2+) concentration) and the fura-2 ratio (340/380 nm), and shortening were measured simultaneously in electrically stimulated myocytes. Myofilament sensitivity to Ca(2+) was assessed from phase-plane diagrams of fura-2 versus cell length by measuring the gradient of the fura-2-cell length trajectory during late relaxation of the twitch contraction. Non-fasting and fasting blood glucose were elevated in GK rats compared to controls. Fasting blood glucose was 151.5 +/- 15.3 mg/dl (n = 8) in GK rats compared to 72.1 +/- 3.6 mg/dl (n = 9) in controls. At 120 min after intraperitoneal injection of glucose (2 g/kg body weight), blood glucose was 570.8 +/- 36.8 mg/dl in GK rats compared to 148 +/- 8.6 mg/dl in controls. Amplitude of shortening was significantly increased in myocytes from GK rats (6.56 +/- 0.54%, n = 31) compared to controls (5.05 +/- 0.43%, n = 36), and the amplitude of the Ca(2+) transient was decreased in myocytes from GK rats (0.23 +/- 0.02 RU, n = 31) compared to controls (0.30 +/- 0.02 RU, n = 36). The fura-2-cell length trajectory during the late stages of relaxation of the twitch contraction was steeper in myocytes from GK rats (89.2 +/- 16.6 microm/RU, n = 27) compared to controls (31.9 +/- 5.9 microm/RU, n = 35). Increased amplitude of shortening, accompanied by a decrease in amplitude of the Ca(2+) transient, might be explained by an increased myofilament sensitivity to Ca(2+).     

Nitrogen Cycles: Past, Present, and Future

This paper contrasts the natural and anthropogenic controls on the conversion of unreactive N₂ to more reactive forms of nitrogen (Nr). A variety of data sets are used to construct global N budgets for 1860 and the early 1990s and to make projections for the global N budget in 2050. Regional N budgets for Asia, North America, and other major regions for the early 1990s, as well as the marine N budget, are presented to Highlight the dominant fluxes of nitrogen in each region. Important findings are that human activities increasingly dominate the N budget at the global and at most regional scales, the terrestrial and open ocean N budgets are essentially disconnected, and the fixed forms of N are accumulating in most environmental reservoirs. The largest uncertainties in our understanding of the N budget at most scales are the rates of natural biological nitrogen fixation, the amount of Nr storage in most environmental reservoirs, and the production rates of N₂ by denitrification.     

Effects of acidosis on ventricular myocyte shortening and intracellular Ca2+ in streptozotocin-induced diabetic rats

We have investigated the effects of acute acidosis on ventricular myocyte shortening and intracellular Ca²⁺ in streptozotocin (STZ)-induced diabetic rat. Shortening and intracellular Ca²⁺ were measured in electrically stimulated myocytes superfused with either normal Tyrode solution pH adjusted to either 7.4 (control solution) or 6.4 (acid solution). Experiments were performed at 35–36°C. At 8–12 weeks after treatment, the rats that received STZ had lower body and heart weights compared to controls, and blood glucose was characteristically increased. Contractile defects in myocytes from diabetic rat were characterized by prolonged time to peak shortening. Superfusion of myocytes from control and diabetic rats with acid solution caused a significant reduction in the amplitude of shortening; however, the magnitude of the response was not altered by STZ treatment. Acid solution also caused significant and quantitatively similar reductions in the amplitude of Ca²⁺ transients in myocytes from control and diabetic rats. Effects of acute acidosis on amplitude of myocyte contraction and Ca²⁺ transient were not significantly altered by STZ treatment. Altered myofilament sensitivity to Ca²⁺ and altered mechanisms of sarcoplasmic reticulum Ca²⁺ transport might partly underlie the acidosis-evoked reduction in amplitude of shortening in myocytes from control and STZ-induced diabetic rat. (Mol Cell Biochem 261: 227–233, 2004)     

Voltage-dependence of contraction in streptozotocin-induced diabetic myocytes

Cardiac contractile dysfunction is frequently reported in human patients and experimental animals with type-1 diabetes mellitus. The aim of this study was to investigate the voltage-dependence of contraction in ventricular myocytes from the streptozotocin (STZ)-induced diabetic rat. STZ-induced diabetes was characterised by hyperglycaemia and hypoinsulinaemia. Other characteristics included reduced body and heart weight and raised blood osmolarity. Isolated ventricular myocytes were patched in whole cell, voltage-clamp mode after correcting for membrane capacitance and series resistance. From a holding membrane potential of –40 mV, test pulses were applied at potentials between –30 and +50 mV in 10 mV increments. L-type Ca²⁺ current (I _Ca,L) density and contraction were measured simultaneously using a video-edge detection system. Membrane capacitance was not significantly altered between control and STZ-induced diabetic myocytes. The I _Ca,L density was significantly (p < 0.05) reduced throughout voltage ranges (–10 mV to +10 mV) in myocytes from STZ-treated rats compared to age-matched controls. Moreover, the amplitude of contraction was significantly reduced (p < 0.05) in myocytes from STZ-treated rats at all test potentials between –20 mV and +30 mV. However, in electrically field-stimulated (1 Hz) myocytes, the amplitude of contraction was not altered by STZ-treatment. It is suggested that in field-stimulated myocytes taken from STZ-induced diabetic hearts, prolonged action potential duration may promote increased Ca²⁺ influx via the sodium-calcium exchanger (NCX), which may compensate for a reduction in Ca²⁺ trigger through L-type-Ca²⁺-channels and lead to normalised contraction. (Mol Cell Biochem 261: 235–243, 2004)     

Anthropogenic nitrogen sources and relationships to riverine nitrogen export in the northeastern U.S.A.

Human activities have greatly altered the nitrogen (N) cycle, accelerating the rate of N fixation in landscapes and delivery of N to water bodies. To examine relationships between anthropogenic N inputs and riverine N export, we constructed budgets describing N inputs and losses for 16 catchments, which encompass a range of climatic variability and are major drainages to the coast of the North Atlantic Ocean along a latitudinal profile from Maine to Virginia. Using data from the early 1990's, we quantified inputs of N to each catchment from atmospheric deposition, application of nitrogenous fertilizers, biological nitrogen fixation, and import of N in agricultural products (food and feed). We compared these inputs with N losses from the system in riverine export.The importance of the relative sources varies widely by catchment and is related to land use. Net atmospheric deposition was the largest N source (>60%) to the forested basins of northern New England (e.g. Penobscot and Kennebec); net import of N in food was the largest source of N to the more populated regions of southern New England (e.g. Charles & Blackstone); and agricultural inputs were the dominant N sources in the Mid-Atlantic region (e.g. Schuylkill & Potomac). Over the combined area of the catchments, net atmospheric deposition was the largest single source input (31%), followed by net imports of N in food and feed (25%), fixation in agricultural lands (24%), fertilizer use (15%), and fixation in forests (5%). The combined effect of fertilizer use, fixation in crop lands, and animal feed imports makes agriculture the largest overall source of N. Riverine export of N is well correlated with N inputs, but it accounts for only a fraction (25%) of the total N inputs. This work provides an understanding of the sources of N in landscapes, and highlights how human activities impact N cycling in the northeast region.