[1] Hydrographs from shallow wells in vegetated riparian zones frequently display a distinctive pattern of diurnal water table fluctuations produced by variations in plant water use. A multisite investigation assessed the major controls on these fluctuations and the ecohydrologic insights that can be gleaned from them. Spatial and temporal variations in the amplitude of the fluctuations are primarily a function of variations in (1) the meteorological drivers of plant water use, (2) vegetation density, type, and vitality, and (3) the specific yield of sediments in the vicinity of the water table. Past hydrologic conditions experienced by the riparian zone vegetation, either in previous years or earlier within the same growing season, are also an important control. Diurnal water table fluctuations can be considered a diagnostic indicator of groundwater consumption by phreatophytes at most sites, so the information embedded within these fluctuations should be more widely exploited in ecohydrologic studies.

Studies involving pharmacologic or molecular biologic manipulation of Group VIA phospholipase A 2 (iPLA 2 ␤) activity in pancreatic islets and insulinoma cells suggest that iPLA 2 ␤ participates in insulin secretion. It has also been suggested that iPLA 2 ␤ is a housekeeping enzyme that regulates cell 2-lysophosphatidylcholine (LPC) levels and arachidonate incorporation into phosphatidylcholine (PC). We have generated iPLA 2 ␤-null mice by homologous recombination and have reported that they exhibit reduced male fertility and defective motility of spermatozoa. Here we report that pancreatic islets from iPLA 2 ␤-null mice have impaired insulin secretory responses to D-glucose and forskolin. Electrospray ionization mass spectrometric analyses indicate that the abundance of arachidonate-containing PC species of islets, brain, and other tissues from iPLA 2 ␤-null mice is virtually identical to that of wild-type mice, and no iPLA 2 ␤ mRNA was observed in any tissue from iPLA 2 ␤-null mice at any age. Despite the insulin secretory abnormalities of isolated islets, fasting and fed blood glucose concentrations of iPLA 2 ␤-null and wild-type mice are essentially identical under normal circumstances, but iPLA 2 ␤-null mice develop more severe hyperglycemia than wild-type mice after administration of multiple low doses of the ␤-cell toxin streptozotocin, suggesting an impaired islet secretory reserve. A high fat diet also induces more severe glucose intolerance in iPLA 2 ␤-null mice than in wild-type mice, but PLA 2 ␤-null mice have greater responsiveness to exogenous insulin than do wild-type mice fed a high fat diet. These and previous findings thus indicate that iPLA 2 ␤-null mice exhibit phenotypic abnormalities in pancreatic islets in addition to testes and macrophages.

. Glucose homeostasis, insulin secretion, and islet phospholipids in mice that overexpress iPLA2␤ in pancreatic ␤-cells and in iPLA2␤-null mice. Am J Physiol Endocrinol Metab 294: E217-E229, 2008. First published September 27, 2007 doi:10.1152/ajpendo.00474.2007.-Studies with genetically modified insulinoma cells suggest that group VIA phospholipase A2 (iPLA2␤) participates in amplifying glucose-induced insulin secretion. INS-1 insulinoma cells that overexpress iPLA 2␤, for example, exhibit amplified insulin-secretory responses to glucose and cAMPelevating agents. To determine whether similar effects occur in whole animals, we prepared transgenic (TG) mice in which the rat insulin 1 promoter (RIP) drives iPLA 2␤ overexpression, and two characterized TG mouse lines exhibit similar phenotypes. Their pancreatic islet iPLA2␤ expression is increased severalfold, as reflected by quantitative PCR of iPLA 2␤ mRNA, immunoblotting of iPLA2␤ protein, and iPLA2␤ enzymatic activity. Immunofluorescence microscopic studies of pancreatic sections confirm iPLA2␤ overexpression in RIPiPLA 2␤-TG islet ␤-cells without obviously perturbed islet morphology. Male RIP-iPLA 2␤-TG mice exhibit lower blood glucose and higher plasma insulin concentrations than wild-type (WT) mice when fasting and develop lower blood glucose levels in glucose tolerance tests, but WT and TG blood glucose levels do not differ in insulin tolerance tests. Islets from male RIP-iPLA 2␤-TG mice exhibit greater amplification of glucose-induced insulin secretion by a cAMP-elevating agent than WT islets. In contrast, islets from male iPLA 2␤-null mice exhibit blunted insulin secretion, and those mice have impaired glucose tolerance. Arachidonate incorporation into and the phospholipid composition of RIP-iPLA2␤-TG islets are normal, but they exhibit reduced Kv2.1 delayed rectifier current and prolonged glucose-induced action potentials and elevations of cytosolic Ca 2ϩ concentration that suggest a molecular mechanism for the physiological role of iPLA2␤ to amplify insulin secretion. transgenic mice; glucose tolerance; insulin tolerance GLUCOSE HOMEOSTASIS REQUIRES that pancreatic ␤-cells secrete insulin when blood glucose concentrations exceed 5 mM. Autoimmune ␤-cell destruction causes type 1 diabetes mellitus, and in type 2 diabetes mellitus, there is 50% loss of ␤-cell mass and impaired insulin secretion and action (12,15). Intensive insulin therapy reduces diabetic complications but increases risks of hypoglycemia (16), and ␤-cell replacement might someday be a superior therapy (59,62).Understanding control of ␤-cell growth, death, and secretion might permit iterative introduction of genes into ␤-cell lines or precursors to optimize secretion, proliferation, and resistance to injury (24,69). Combined with empirical selection and encapsulation, such ␤-cell engineering might someday provide a renewable source of ␤-cells for replacement therapy (44,45). Developing such potential future therapies requires increased understanding of the genes and gene products that gov...

An experimental and numerical study on laminar flame characteristics of methane oxy-fuel mixtures highly diluted with CO 2 was conducted using a constant volume chamber and CHEMKIN package. The effects of high CO 2 dilution on combustion chemical reaction, flame instability, and flame radiation of CH 4 /CO 2 /O 2 mixtures were studied. The laminar burning velocities of CH 4 /CO 2 /O 2 mixtures decrease with the increase of the CO 2 fraction. CO 2 directly participates in the chemical reaction through the elementary reaction OH + CO = H + CO 2 and inhibits the combustion process by the competition of the H radical between the reverse reaction of OH + CO = H + CO 2 and the reaction H + O 2 = O + OH. This effect is more obvious for highly diluted CO 2 in the case of CH 4 /CO 2 /O 2 mixtures. CO 2 suppresses the flame instability by the combined effect of hydrodynamic and thermal-diffusive instabilities. The radiation of CH 4 oxy-fuel combustion is much stronger than that of CH 4 / air combustion mainly because of the existence of a large fraction of CO 2 in CH 4 /CO 2 /O 2 flames, which will influence the wall temperature and temperature distribution in the gas turbine combustor.

Studies involving pharmacologic inhibition or transient reduction of Group