Level Of Pi Research Articles

Endogenous phospholipid metabolism in stimulated neutrophils differential activation by FMLP and PMA

Endogenous phospholipid metabolism was examined during the initial 0–120 seconds of neutrophil (PMN) stimulation. When PMN were exposed to the chemotactic peptide FMLP (10 −7 M) or the tumor promotor, phorbol myristate acetate (PMA, 1 μg/ml) extensive changes in specific phospholipid (PL) classes were evident within 15 seconds. The profile and kinetics of stimulus-induced PL changes were stimulus-dependent. Five seconds after the addition of FMLP, PMN content of PC, PS and PA increased, while the level of PI decreased. Kinetic studies revealed that only PA levels remained elevated (0–120 s) while other PL decreased. In contrast, when cells were exposed to PMA (1 μg/ml), the levels of PC and PS rapidly increased (< 15 s). With PMA as stimulus, changes in PI and PA were not observed until > 60 s. Results indicate that exposure to PMN to stimuli leads to rapid changes in specific PL. In addition, they support the concept that neutrophils rapidly “remodel” endogenous PL upon stimulation.

Effects of Excess Methionine Ingestion on Hepatic Phosphate, Adenine Nucleotides and Free Amino Acids in the Rat

Adult male rats were force-fed either a single dose of 200 mg of dl-methionine or an amino acid mixture with the pattern of casein. The animals were anesthetized with pentobarbital at 0, 1.5, 3 and 4 hours after intubation, and samples of liver were removed by a freeze-clamping technique at 0, 15 and 30 seconds of ischemia. Hepatic ATP, ADP, AMP, Pi, glucose-6-phosphate, glucose and certain nitrogenous compounds as well as plasma glucose were determined. After methionine was given by intubation, hepatic methionine and glutathione increased severalfold within 1.5 hours; cystathionine showed a transient rise at this time but returned to normal at 3 and 4 hours, when taurine was progressively increasing. Several nonessential amino acids decreased, suggesting that they may be utilized for energy. Methionine forcefeeding did not modify the concentration of hepatic adenine nucleotides and probably did not change their turnover, as estimated from changes during ischemia. The level and production of Pi during ischemia was increased however. After force-feeding the amino acid mixture, hepatic methionine, cystathionine and taurine were unaffected, and glutathione increased only at hours 3 and 4; glycine and threonine were elevated by 1.5 hours. Hepatic adenine nucleotides, inorganic phosphate and glucose were not significantly affected by the feeding of amino acids by intubation.methionine ischemia adenine nucleotides inorganic phosphate glutathione

Fructosebisphosphatase of Plant Roots

Summary A specific fructosebisphosphatase has been identified in pea and maize roots. It was separated from a non-specific phosphatase and partially purified using ammonium sulphate fractionation and chromatography on DEAE cellulose. The root fructosebisphosphatase appeared to be located in the cytosol. Enzyme activity was Mg 2+ -dependent (the Km for Mg 2+ being 0.15 mM), and was observed at all pH values between 6.5 and 8.5. The concentration of fructose-1,6-P 2 required for half maximal activity ranged from 0.06 mM to 0.36 mM, depending on the pH and level of Pi; it was increased when either the Pi concentration was raised from 0.14mM to 5 mM, or when the pH was lowered from 8.0 to 7.1. Unlike most fructosebisphosphatases, the root enzyme was not affected by AMP. However, Pi stimulated enzyme activity, particularly at higher pH and with higher fructose-1,6-P 2 concentrations, and preliminary evidence was obtained for strong inhibition by fructose-6-P. The physiological role of fructosebisphosphatase in roots is not clear, but the possibility that it functions in cytosolic gluconeogenesis during periods of anaerobiosis, or during conversion of amyloplast starch to sucrose, is considered.

Plasma level and renal handling of Pi: effect of overnight fasting with and without Pi supply.

Overnight fasting significantly increases plasma inorganic phosphate ([Pi]p) in rats previously fed low Pi diet (LPD), whereas it slightly decreases [Pi]p in rats previously fed high Pi diet (HPD). We assessed the role of the kidney in these differing responses by investigating the influence of overnight fasting on renal tubular capacity to reabsorb Pi by clearance technique in conscious rats. To also evaluate the effect of Pi deprivation during overnight fasting three groups of animals were studied: fed, completely fasted, and fasted with a Pi supply in the drinking water. In intact LPD and HPD rts the tubular Pi reabsorptive capacity was not different between fed and completely fasted rats. It was, however, found to be lower in fasted but Pi-supplied than in fed animals, indicating a decrease by overnight fasting with respect to all nutrients except Pi, i.e., by fasting per se. Conversely, it was higher in the animals completely fasted than in those fasted but Pi-supplied, showing an increase by overnight Pi deprivation. These two opposite effects explain the absence of any significant influence of overnight complete fasting on tubular Pi handling. The same results were obtained in thyroparathyroidectomized rats on low Pi intake. This study shows that the kidney can adapt its transport capacity for Pi according to changes in Pi supply within 12 h. It also suggests that it may react by a decrease in reabsorption to the reduction in Pi utilization that can be expected to occur during fasting per se. Furthermore, our data explain how the kidney, by adapting its tubular Pi transport to the prior dietary intake of Pi, can account for the difference in phosphatemic response to overnight fasting and consequently in the diurnal fluctuation of [Pi]p observed between LPD and HPD animals.

On the role of inorganic phosphate in divalent-cation sequestration by mitochondria.

Rat liver mitochondria which have actively accumulated Mn2+ ions exhibit an electron para-magnetic resonance (EPR) spectrum dominated by a component E in which the usual hyperfine sextet has been collapsed to a single line through the process of spin exchange narrowing. When uptake occurs in the absence of added Pi, the line width of E shows considerable variation. By comparing experimentally observed spectra with computer-generated simulations it is demonstrated however that, under these conditions, E can be as narrow as approximately equal to 190 Oe, considerably narrower than the spectrum from a manganese phosphate precipitate. Furthermore parallel quantification on a single mitochondrial sample shows the level of Pi to be several times lower than the amount of Mn2+ observable in E. It is concluded therefore that the spectral component E, obtained under these conditions, cannot be accounted for in terms of manganese phosphate precipitate. These findings further indicate that a substantial number of sites (approximately equal to 100 nmol/mg protein), other than Pi, must exist inside the mitochondria which are capable of complexing divalent cations in regions of high local concentration.

Studies on the mechanism of Ca2+ stimulation of plasminogen activator synthesis/release by Swiss 3T3 cells.

Stimulation of postconfluent Swiss 3T3 cells in serum-free medium with 4.3 mM Ca2+ results in marked increases in both released and cell-associated plasminogen activator (PA). Increased release of PA commenced approximately 10 to 12 hours post-stimulation and continued to increase steadily until 48 hours at which time the stimulates cells (4.3 mM Ca2+) released approximately 14 times more PA than control cells (1.8 mM Ca2+). Sr2+, like Ca2+, also stimulates PA synthesis/release either in the presence or in the absence of 1.8 mM Ca2+ whereas an excess of Mg2+ inhibits Ca2+ stimulation. Supranormal [Pi] in the medium stimulates PA synthesis/release in the presence of 1.8 mM mM Ca2+. Further, optimal stimulation by 4.3 mM Ca2+ requires a normal level of Pi (1.0 mM). Elevation of medium [Ca2+] or [Pi] results in an enhanced uptake of Ca2+. The facts that cycloheximide treatment completely abolishes the Ca2+ stimulatory effect and that an increase in cell associated PA precedes release indicate that PA release is coupled to synthesis of new PA. Ca2+ stimulation of PA synthesis/release also requires continuous energy production and RNA as well as protein synthesis. A hypothesis is proposed to explain the relationship between stimulation of PA production and its enhanced release from cells stimulated by elevated [Ca2+] or [Pi] in the media. The possibility that PA release may be an example of the phenomenon of membrane shedding as opposed to secretion is discussed.

Resistance to the phosphaturic and calcemic actions of parathyroid hormone during phosphate depletion. Prevention by 1,25-dihydroxyvitamin D3.

Recent observations indicate that in thyroparathyroidectomized (TPTX) rats fed a low (0.2 g/100 g) phosphorus diet, the tubular phosphaturic response to parathyroid hormone (PTH) remains markedly blunted even when it is assessed at normal or high plasma concentration and filtered load of inorganic phosphate (Pi). Because 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] decreases the tubular capacity to reabsorb Pi when chronically administered to TPTX rats, we have studied whether this vitamin D(3) metabolite could specifically increase the phosphaturic response to PTH in phosphate-deprived animals. The results show that in Vitamin D-replete TPTX rats fed a low (0.2 g/100 g) phosphorus diet, 1,25(OH)(2)D(3) (2 x 13 pmol/d i.p. for 7 d) markedly enhanced the acute tubular phosphaturic response to PTH (2.5 IU/h i.v.) without affecting the action of the peptide hormone on Ca reabsorption and cyclic-3',5'-AMP excretion. The influence of 1,25(OH)(2)D(3) on the phosphaturic response to PTH could not be ascribed to an increased plasma concentration and(or) filtered load of Pi during the administration of the peptide hormone. However, it could be, at least in part, related to the elevation in the basal level of plasma Pi which was observed in the 1,25(OH)(2)D(3)-treated animals. The results also indicate that 1,25(OH)(2)D(3) significantly enhanced the calcemic response to PTH, which was blunted in these conditions of phosphate deprivation. Unlike 1,25-(OH)(2)D(3), 25-hydroxyvitamin D(3) did not unmask the phosphaturic effect of PTH in phosphate-depleted animals, even when given in doses 100 times larger. Thus, 1,25(OH)(2)D(3) displays a selective and powerful activity in preventing the occurrence of tubular resistance to the phosphaturic action of PTH during Pi depletion. This finding suggests the existence of an important interaction between dietary Pi, 1,25(OH)(2)D(3), and PTH in the homeostasis of phosphate.

The a3Πr-x1Σ+transition of SiS

The a3 Pi r( Omega =1)-x1 Sigma + transition of SiS has been obtained in emission. A v progression (with v' assumed to be 0) of five bands has been observed in this system. The analysis of the 0-6 band yields the rotational constant for the v=0 level of the a3 Pi r state. The position of the a3 Pi r( Omega =1) state relative to the ground state ( nu 00) has also been calculated.

Regulation of Escherichia coli K10 aminoendopeptidase synthesis. Effects of mutations involved in the regulation of alkaline phosphatase.

The synthesis of alkaline phosphatase in Escherichia coli is controlled by the action of at least four genes denoted phoS, phoT, phoR and phoB. The effect of mutations in the first three of these genes on the synthesis of periplasmic aminoendopeptidase of E. coli K 10 have been investigated. phoR gene product does not seem to be involved either in the constitutive or in the derepressed synthesis of this enzyme. Mutations in phoS or phoT influence the intracellular level of Pi in much the same way as depletion of Pi from the growth medium, and only as a consequence influence the synthesis of aminoendopeptidase and alkaline phosphatase. Point, amber or deletion mutations in the alkaline phosphatase structural gene do not affect aminoendopeptidase synthesis. Thus, alkaline phosphatase and 'derepressed' aminoendopeptidase synthesis are co-regulated by the endogenous level of inorganic phosphate. The way by which this regulation operates is discussed.

THE PROBLEM OF TISSUE OXYGENATION IN DIABETES MELLITUS

Evidence for a causative relationship between prolonged tissue hypoxia and diabetic retinopathy and glomerulosclerosis are presented. Based on the assumption that one of the most fundamental requirements for optimal cellular metabolism is a constant cellular oxygen tension, the "three-in-one concept" for the development of diabetic microangiopathy is formulated. The term "three-in-one" is employed because this concept partly or completely includes "the glycoprotein-", "the hypoxia-", and "the growth hormone hypothesis". Diabetics show evidence of variability in the tissue oxygen availability/demand ratio which is compensated by three self-regulating factors: 1) an increase in local flow, 2) an increase in red cell 2,3-DPG leading to a shift to the right of the oxyhaemoglobin dissociation curve, and 3) an increase in the oxygen-binding capacity or the haemoglobin concentration. The level of plasma inorganic phosphate (Pi) is of importance in maintaining high 2,3-DPG levels. However, since Pi fluctuates depending upon changes in the control of diabetes, the regulatory mechanism of the 2,3-DPG modulated unloading of oxygen from the erythrocytes often becomes insufficient, and therefore in poorly regulated diabetics with less than optimal 2,3-DPG levels, the main load of compensation against tissue hypoxia is placed on an adjustment in the microcirculation of the organ involved. However, in order for the microvascular dilatation to occur, the cells must experience a hypoxic stimulus. The summation of the infinite number of discrete and occasionally pronounced hypoxic injuries to the tissue cells in association with the adverse effect of local vasodilatation with increased plasma permeation through the vessel walls might over the years lead to diabetic microangiopathy. Based on this theory the high level of Pi in diabetes becomes of particular significance. Our experience with a high phosphate diabetes diet in the treatment of diabetics is presented. This dietary regimen leads to a significant increase in the oxygen release capacity of the erythrocytes, suggesting an improvement in tissue oxygenation, and may therefore become of value in the prophylaxis of diabetic microangiopathy.

Phosphate mobilization in grains of Hordeum distichon

When decorticated grains were germinated at 14·5°, inorganic substances moved from the endosperm, mainly the aleurone layer, to the embryo. The level of Pi rose in the embryo and endosperm, and the embryo appeared to accumulate Pi against a concentration gradient. The level of organic-P declined in the endosperm, particularly in the alcurone layer. Separated aleurone layers, incubated at 25°, released only small amounts of organic or inorganic phosphate. However, when incubated with gibberellic acid (GA 3), a massive release of Pi occurred at the expense of organic phosphates within the tissue. This release followed a sigmoid pattern with time following a lag and was virtually complete in 6 days. Allowing the aleurone layer to dry before incubating with GA 3 reduced or abolished the lag period of Pi release and only marginally depressed the total amount ultimately freed. In contrast, α-amylase production was depressed by the longer periods of drying. The major phosphate of the aleurone was phytate ( meso-inositol hexaphosphate, IP 6), but traces of 1P 4, IP 3, IP 2, IP 1, Pi and unidentified phosphates were detected. During incubation with GA 3 the IP 6 content fell, and the lower esters of inositol rose slightly and then fell in a pattern indicating that the phosphate groups of each IP 6 molecule were being sequentially hydrolysed. After 6 days incubation, the tissue phosphates were reduced to a very low level. Attempts to isolate aleurone grains containing phytate were unsuccessful.