Abundant Cation Research Articles

Inward-Rectifying K+ Channels in Root Hairs of Wheat (A Mechanism for Aluminum-Sensitive Low-Affinity K+ Uptake and Membrane Potential Control).

K+ is the most abundant cation in cells of higher plants, and it plays vital roles in plant growth and development. Extensive studies on the kinetics of K+ uptake in roots have shown that K+ uptake is mediated by at least two transport mechanisms, one with a high and one with a low affinity for K+. However, the precise molecular mechanisms of K+ uptake from soils into root epidermal cells remain unknown. In the present study we have pursued the biophysical identification and characterization of mechanisms of K+ uptake into single root hairs of wheat (Triticum aestivum L.), since root hairs constitute an important site of nutrient uptake from the soil. These patch-clamp studies showed activation of a large inward current carried by K+ ions into root hairs at membrane potentials more negative than -75 mV. This K+ influx current was mediated by hyperpolarization-activated K+-selective ion channels, with a selectivity sequence for monovalent cations of K+ > Rb+ [almost equal to] NH4+ >> Na+ [almost equal to] Li+ > Cs+. Kinetic analysis of K+ channel currents yielded an apparent K+ equilibrium dissociation constant (Km) of [almost equal to]8.8 mM, which closely correlates to the major component of low-affinity K+ uptake. These channels did not inactivate during prolonged stimulation and would thus enable long-term K+ uptake driven by the plasma membrane proton-extruding pump. Aluminum, which is known to inhibit cation uptake at the root epidermis, blocked these inward-rectifying K+ channels with half-maximal current inhibition at [almost equal to]8 [mu]M free Al3+. Aluminum block of K+ channels at these Al3+ concentrations correlates closely to Al3+ phytotoxicity. It is concluded that inward-rectifying K+ channels in root hairs can function as both a physiologically important mechanism for low-affinity K+ uptake and as regulators of membrane potential. The identification of this mechanism is a major step toward a detailed molecular characterization of the multiple components involved in K+ uptake, transport, and membrane potential control in root epidermal cells.

Acid rain and soils of the Adirondacks. III. Rates of soil acidification in a montane spruce–fir forest at Whiteface Mountain, New York

To assess the impact of atmospheric deposition on soil acidification and base cation supplies in montane spruce–fir forest soils at Whiteface Mountain, New York, base cation and proton fluxes were determined for organic and mineral horizons from measurements made at four stands (1020–1090 m above sea level) over a 4-year period. Our best estimates indicate an annual accumulation of H+ and a net loss of base cations from the forest floor of about 0.71 kmolc/ha, a 2.8% per year loss of the total forest floor base cation pool. This high rate of acidification is attributable to base cation leaching by sulfate and organic anions, and uptake by living biomass. From 1986 to 1990, the annual net loss rate of forest floor Ca, the most abundant base cation, was several times greater than historical loss rates as determined by 50-year comparisons of forest floor Ca in nearly identical forests of the Adirondack High Peaks region. Published data on long-term trends in Ca deposition in the U.S. Northeast suggest that the difference between historical and current net loss rates of forest floor Ca may be due to sharply reduced atmospheric inputs of Ca after about 1970, exacerbated by sulfate leaching. In mineral horizons where the total base cation pool (mostly mineral bound) is very large, the net losses of base cations were substantially lower and in the range where losses due to leaching and uptake can be countered by mineral weathering.

Introduction: Importance of Mg in physiology and medicine and the need for ion selective electrodes

Mg is a co-factor in more than 325 enzyme systems in cells and is the second most abundant intracellular cation after K. It is important in numerous physiologic and homeostatic functions such as hormone-receptor binding, gating of Ca2+ channels, transmembrane flux of ions, regulation of adenylate cyclase, Ca(2+)-Ca(2+) release, muscle contraction, cardiac excitability, neuronal activity, control of vasomotor tone and neurotransmitter release, to name a few. Serum total Mg measurements suggests this extracellular cation is often lowered in many hospitalized patients. It appears to be greatly depleted in normal food preparation and processing. Its daily intake has been declining steadily in the USA from where it was about 500 mg/day, at the turn of the century, to where it is now about 175-225 mg/day. Most mammals exhibit very similar levels of extracellular Mg, including humans. This might suggest that total Mg measurements on serum or plasma aren't sensitive blood variables or analytes to reflect what may be going on in the body at the cellular level. Mg exists in several forms in the blood, but the ionized, free Mg is probably the most physiologically important fraction, thus pointing to a need for sensitive, specific ion selective electrodes. Our studies, so far, suggest that ISE's can be designed which will work equally well on whole blood, serum and plasma to measure IMg2+ in healthy and diseased subjects.

Magnesium in the 1990's: Implications for Veterinary Critical Care

SummaryMagnesium is the second most abundant intracelular cation, exceeded only by potassium. The majority of magnesium is found in bone and muscle. This cation is required for many metabolic functions, most notably as a coenzyme for the sodium‐potassium ATPase pump. Magnesium functions to maintain the electrolyte gradient across all membranes. Interference with this gradient may result in changes in the resting membrane potential and disturbances in repolarization, resulting in cardiovascular and neuromuscular abnormalities.Hypomagnesemia may be the most underdiagnosed electrolyte disorder. Incidence rates greater than 50 percent have been reported in critically ill human patients. Currently there is little or no information available regarding the incidence and significance of hypomagnesemia in hospitalized animals. Causes of magnesium deficiency can be divided into four general categories: gastrointestinal, renal, endocrine and miscellaneous. The diagnosis of magnesium depletion can be difficult since less than one percent of total body magnesium is located in serum. Alternative methods of evaluating magnesium status include determining ultrafilterable magnesium levels, mononuclear blood cell magnesium levels or by quantifying magnesium retention of an administered loading dose.

Water quality of different aquifers in Saudi Arabia and its predictive effects on soil properties

Abstract Chemical composition data of different aquifers was used to classify groundwaters in Saudi Arabia. For the mean water composition, different water quality parameter ranges were for EC, 1.56 to 8.24 dS m‐1; total dissolved solids (TDS), 1200 to 4860 mg L‐1; sodium adsorption ratio (SAR) 3.10 to 12.53; Ca2+/ Mg2+ ratio, 0.80 to 3.15; and Cl‐/SO2‐ 4 ratio, 0.49 to 3.68. For the 90th percentile water composition, the water quality parameter ranges were for EC, 2.26 to 13.10 dS m‐1; TDS, 1950 to 9800 mg L‐1; SAR, 3.45 to 18.76; Ca2+/Mg2+ ratio, 0.58 to 3.49; and Cl‐/SO2‐ 4 ratio 0.40 to 4.85. Sodium was found to be the most abundant cation, followed by Ca2+, and Mg2+. Cl‐ and SO2‐ 4 were present in a balanced proportion, followed by HCO‐ 3. The waters were classified as C 3 S 1 to C 4 S 4, i.e., a category of high to very high salinity and low to very high sodicity problem water. Other parameters such as adj. SAR, adj. RNa+, and ESP were calculated, interrelated, and commented upon for possible salini...

The Rationale of Magnesium Supplementation in Acute Myocardial Infarction

Magnesium is the second most abundant intracellular cation in the human body, next to potassium, and is involved in more than 300 different enzymatic reactions, including glucose use; the synthesis of fat, protein, and nucleic acids; the metabolism of adenosine triphosphate; muscle contraction; and some membrane transport systems. 1,2 Over recent years, evidence has accumulated that patients with acute myocardial infarction (AMI) are magnesium deficient 3,4 and develop an increased hypomagnesemia during the acute phase of the infarct. 5-8 Hypomagnesemia might be due to migration from extracellular to intracellular space, 9 which is caused by catecholamine-induced lipolysis forming in soluble magnesium soaps, as demonstrated in animal experiments. 6,10,11 Furthermore, experiments in animals and humans have shown that the acute as well as the chronic reduction in extracellular magnesium levels are harmful to the myocardium in the setting of acute ischemia. 12-14 While the metabolism of magnesium in AMI and the incidence

Regulation of cell magnesium

Magnesium is the second most abundant cation within mammalian cells, trailing only potassium. It is also in- dispensable in the cell for a score of reactions and func- tions: it activates a large number of enzymes either di- rectly or by forming complexes with and modifying substrates; it maintains proper conformations of nucleic acids and proteins; it regulates the operation of channels, receptors, and intracellular signalling molecules; it mod- ulates photosynthesis, oxidative phosphorylation, muscle contraction, and nerve excitability; it is indispensable for cell growth and for controlling cell cycle (1, 2). It is thus amazing that we know so little about the cellular homeostasis of Mg2+ and its control. During the past several decades, all the other major cellular cations have engrossed the interest of biological researchers and this has resulted in a detailed elucidation of the various mechanisms of cellular Ca2+, H’, K+, or Na+ homeostasis. In fact, the number of recent published observations for each of these cations is so staggering that it would put the writer in a quandary to write a small review not only on their cellular control but also on individual compo- nents, organelles, or enzymes involved in specific steps of this control. This is not the case for Mg2+, for which observations in the literature related to its cellular control are sparse, despite some encouraging recent progress. The reasons for this limited knowledge are several, but the most prominent reason is that the techniques available for measuring cell Mg2+ are a far cry from those available for measuring other cations. Compounding this deficiency is the fact that the free Mg2+ concentration in cells is high, several orders of magnitude greater than that of Ca2+ or H+. Because of this, even large changes in intra- cellular Mg2+ mobilization represent only a small fraction

Segregation of ore metals between magmatic brine and vapor; a fluid inclusion study using PIXE microanalysis

Nondestructive proton-induced X-ray emission (PIXE) analysis is used to measure the concentrations of base metals and other heavy elements in single hypersaline brine inclusions and low-salinity vapor inclusions, which are intimately associated within a granite-hosted quartz-cassiterite vein in the Mole Granite (New South Wales, eastern Australia). Microther-mometric measurements and Raman microspectrometry on the same inclusions complement the data.The brine inclusions have an estimated composition (in wt %): NaCl, 20; KCl, 7; CaCl 2 , 0.9; MnCl 2 , 4; FeCl 2 , 14; ZnCl 2 , 1; plus (in ppm by weight) Co, 300; Cu, 900; As, 500; Br, 400; Rb, 1,700; Sn, approximately 400; Cs, 2,000; Pb, 3,000. Cation ratios in this brine compared with trace element concentrations in the source granite closely match experimental data on equilibrium metal distribution between chloride-bearing aqueous fluid and silicate melts, confirming that the brine inclusions represent near-pristine samples of magmatic fluid.Low-salinity vapor inclusions occurring in the same sample are interpreted on the basis of phase equilibria to have coexisted with the magmatic brine at 500 degrees to 600 degrees C and 500 to 800 bars, prior to some cooling and decompression to trapping conditions of 380 degrees to 450 degrees C and approximately 300 bars. Compared with the brine inclusions, they contain higher concentrations of CO 2 and S (of unknown speciation) and about 1 percent Cu as the most abundant cation detected by PIXE analysis. Concentration ratios of copper to all other first-row transition metals (e.g., Cu/Fe, Cu/Zn, and also Cu/Pb) are more than two orders of magnitude higher in the vapor than in the brine inclusions.The fluid inclusion results indicate that partitioning of base and precious metals between magmatic vapor and hypersaline brine may be substantial and highly element specific, probably as a result of contrasting metal complexing in the two fluid phases. Volatile sulfur complexes of copper could explain preferential partitioning of copper (and by inference, of gold) into the magmatic vapor phase, whereas chloride complexing causes most other heavy metals to partition into the coexisting brine. The analytical data emphasize the importance of magmatic vapor and vapor condensate as ore-forming solutions and suggest that brine-vapor separation may be an important mechanism of base and precious metal segregation in high-temperature hydrothermal systems. This possibility has not received much attention so far, but could be a significant factor in the formation of porphyry-style and other magmatic hydrothermal base and precious metal deposits.

Role of extracellular magnesium in insulin secretion from rat insulinoma cells.

Magnesium (Mg2+) is an abundant intracellular cation that participates in the regulation of the intracellular concentration of ATP. In this study, we examined the relationship between insulin secretion and intracellular free Mg2+ ([Mg2+]i) in a rat-insulinoma cell line (RIN m5F), using a fluorescent dye (Mag-fura-2). KCI, forskolin, and D-glyceraldehyde increased [Mg2+]i and insulin secretion from RIN m5F cells in a dose-dependent fashion. Verapamil, a voltage-dependent Ca2+ channel blocker, inhibited the increase of [Mg2+]i that was evoked by KCI, forskolin, and D-glyceraldehyde. In a Mg(2+)-free buffer, these agents failed to cause an elevation in [Mg2+]i; however, the insulin response to KCI and forskolin was enhanced, compared with that in the presence of Mg2+ (1.25 mM). Our findings suggest that [Mg2+]i is dependent upon extracellular Mg2+, and the influx through the voltage-dependent Ca2+ channel. Mg2+ may competitively inhibit the voltage-dependent Ca2+ channel, which is known to play a role in insulin secretion. An absence of Mg2+ in the extracellular space may result in enhanced insulin secretion. [Mg2+]i may play a role in insulin secretion from RIN m5F cells.

Mechanisms of Magnesium Transport

Mg, the second or third most abundant intracellular cation, is an important constituent of cells and is a necessary cofactor for many enzymes especially those involved in the transfer of phosphate groups. In this role Mg is essential for Na and Ca pump activity. Recently it has been shown to regulate the activity of the Na,K,CI (18) and K,CI (39) co-transport systems and to influence ionic traffic through Ca (34), K (37), and Na (48) channels. Mg may thus be an important link between ion transport and metabolism, and it is likely that its cytoplasmic concentration is precisely regulated. This chapter will focus on how Mg crosses the membrane and on some of the factors that influence the process. It will show how models initially formulated to de­ scribe Mg transport in squid axon and barnacle muscle have been used to explain recent observations on red cells. The earliest experiments on Mg transport suggested it was difficult to change cell Mg content. Several cell types had been incubated for long periods in media containing either high Mg concentrations or Mg chelators without significantly affecting cell Mg content. This, together with the observation that 28Mg equilibrated very slowly across some cell membranes, suggested that membranes had a particularly low Mg permeability (17, 19)

Metal chemistry of irrigation and drainage waters of Al-Ahsa Oasis of Saudi Arabia and its effects on soil properties

Water samples from 18 springs and 13 drainage canals and subcanals were collected from Al-Ahsa Oasis. Concentrations of total dissolved salts, Cl, SO4 HCO3, B, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, V, Ti, and Zn were determined. The soil salinity development (SSD), the adjusted Na ratio (adj. SAR), the adjusted Na adsorption ratio (adj. RNa), and exchangeable Na percentage (ESP) were calculated. Sodium was the most abundant cation in all water samples followed by Ca, Mg, Sr, and K in descending order. Concentrations of all other metals were below 0.1 mg L−1. Chloride was the most abundant anion, followed by SO4 and HCO3 in these waters. A significant correlation (P 16 meq L−1, Mg was doubled, and Na and Cl increased several times in the drainage waters. The salinity and sodicity hazards of the spring and drainage waters were classified as C4S2 i.e. high salinity with medium sodicity problems.

The Role of Magnesium in Clinical Biochemistry: An Overview

Magnesium is the second most abundant intracellular cation. It is essential for a wide variety of metabolically important reactions, in particular those involving ATP. Hypomagnesaemia is surprisingly common in hospital populations but is sometimes either undetected or overlooked. Serum magnesium concentrations provide a guide to magnesium status but while hypomagnesaemia is a reliable indicator of magnesium deficiency, normomagnesaemia does not exclude magnesium depletion. A wide variety of conditions predispose to magnesium depletion. Clinical magnesium deficiency has potentially fatal consequences in vulnerable groups of patients and should be excluded in all such cases. Magnesium deficiency may result in hypokalaemia, hypocalcaemia or other disturbances of electrolyte homeostasis, refractory cardiac arrhythmias, or increased sensitivity to digoxin. The capacity to measure serum and urine magnesium concentrations rapidly, regularly and reliably should be part of the repertoire of all clinical chemistry laboratories involved in the care of critically ill patients.

Fast atom bombardment mass spectra of stibonium salts

AbstractThe positive‐ion fast atom bombardment (FAB) mass spectra of stibonium salts have been studied. The spectra exhibit an abundant intact cation (C+) and fragment ions resulting from the loss of R, R′ or stable neutral species from the cation. The principal fragment ions in the FAB mass spectra of stibonium salts are [R3Sb]+·, [R2Sb]+, [R2SbH2]+, [RSbR′]+, [RSbH]+, [RSb − H]+ and [R2SbR']+·. In most cases, [ M + C] + cluster ions were detected. When the anion was bromine, the adduct ions [M + (R − H)Sb]+, [C + (R‐H)]+ and [ C + (R′ − H)]+ were also observed, whereas when the anion was [BPh4]−, interesting cluster ions such as [M + (BR′ ‐ H)]+ and [M + (BR′ − 3H)]+ appeared.

Regulation of mammalian melanogenesis II: the role of metal cations

Melanogenesis can be divided into two phases. The first one involves two tyrosinase-catalyzed oxidations from tyrosine to dopaquinone and a very fast chemical step leading to dopachrome. The second phase, from dopachrome to melanin, can proceed spontaneously through several incompletely known reactions. However, some metal transition ions and protein factors different from tyrosinase might regulate the reaction rate and determine the structure and relative concentrations of the intermediates. The study of the effects of some divalent metal ions (Zn, Cu, Ni and Co) on some steps of melanogenesis pathway has been approached using different radiolabeled substrates. Zn(II) inhibited tyrosine hydroxylation whereas Ni(II) and Co(II) were activators. Ni(II), CU(II) and Co(II) accelerated chemical reactions from dopachrome but inhibited its decarboxylation. Dopachrome tautomerase also decreased decarboxylation. When metal ions and this enzyme act together, the inhibition of decarboxylation was greater than that produced by each agent separately, but amound of carboxylated units incorporated to the melanin was not higher than the amount incorporated in the presence of only cations. The amount of total melanin formed from tyrosine was increased by the presence of both agents. The action of Zn(II) was different from other ions also in the second phase of melanogenesis, and its effect on decarboxylation was less pronounced. Since tyrosine hydroxylation is the rate-limiting step in melagonesis, Zn(II) inhibited the pathway. This ion seems to be the most abundant cation in mammalian melanocytes. Therefore, under physiological conditions, the regulatory role of metal ions and dopachrome tautomerase does not seem to be mutually exclusive, but rather complementary.

Hormonal control of Mg2+ transport in the heart

Magnesium is abundant in the mammalian body and the second most abundant cation in cells. Because the concentration of intracellular free Mg2+ is relatively high (0.2-1 mM), Mg2+ is unlikely to act as a second messenger, like Ca2+, by rapidly changing its cytosolic concentration. But changes in Mg2+ do have profound effects on cellular metabolism, structure and bioenergetics. Key enzymes or metabolic pathways, mitochondrial ion transport, Ca2+ channel activities in the plasma membrane and intracellular organelles, ATP-requiring reactions, and structural properties of cells and nucleic acids are modified by changes in Mg2+ concentration. Yet, although some information is available from giant cells and bacteria, little is known about the regulation of intracellular Mg2+ in mammalian cells. Here we report a new transport mechanism for Mg2+ across the sarcolemma of cardiac cells in both intact hearts and dissociated myocytes. We show that noradrenaline, through beta-adrenergic stimulation and increase of cyclic AMP, stimulates a large efflux of Mg2+ from cardiac cells. This transport is of major dimensions and can move up to 20% of total cellular Mg2+ within a few minutes.

The role of magnesium in cardiac arrhythmias

T HE RELATIONSHIP between electrolyte deficiencies and the development and prevention of cardiac arrhythmias has been a subject of continued interest in the medical literature. Studies have suggested a correlation between certain electrolyte deficiencies, such as hypokalemia, and the occurrence of arrhythmias and sudden death.le6 Recent interest, however, has focused on magnesium (Mg) deficiency and its role in this area. Interest in Mg may be related to the recognition of the extensive role this cation plays in a multitude of human physiological processes. Mg is the second most abundant intracellular cation in the human body and is involved in over 300 different enzymatic reactions including: glucose use; the synthesis of fat, protein, and nucleic acids; the metabolism of adenosine triphosphate (ATP); muscle contraction; and some membrane transport systems. Effects of Mg on atrioventricular (AV) nodal conduction, the transmembrane potential, and arrhythmias have also been postulated.‘*7-12 Total body Mg stores approximate 1,000 mmol/L with 1% present extracellularly, 60% present in skeletal tissue, and 39% present intracellularly.’ A normal homeostatic level of Mg is maintained via a balance between gastrointestinal absorption and renal excretion. Gastrointestinal net absorption is approximately 35% to 40% of an orally administered load and occurs almost exclusively via the small intestine. Mg loss occurs primarily via renal excretion and averages only 3% to 5% of a filtered load. Over 65% of Mg reabsorption occurs in the thick ascending limb of Henle and, depending on the Mg concentration in plasma, excretion may range from 10 to 5,000 mg over a 24-hour period.274F7,97’0*‘3-15 Despite the apparent ability of the human body to maintain Mg homeostasis through intestinal and renal processes, Mg deficient states occur and are being increasingly recognized. Two studies have documented the prevalence of Mg deficiency in hospitalized patients.‘6-‘8 In one study the prevalence of hypomagnesemia was determined in 2,300 patients in a Veteran’s Administration hospital.16*” When hypomagnesemia was defined as a serum Mg concentration less than 1.25 mEq/L the prevalence of hypomagnesemia was 6.9%. In another study Wong et all8 determined serum magnesium levels in 621 samples of randomly selected hospitalized patients and found hypomagnesemia (< 1.2 mEq/ L) in 11%. The causes of hypomagnesemia are many and varied and include: nutritional causes secondary to prolonged parenteral fluid administration, starvation with metabolic acidosis, protein-calorie malnutrition, Kwashiorkor, or alcoholism; intestinal causes secondary to chronic diarrhea or a malabsorption syndrome; renal causes secondary to disease-related states such as renal tubular acidosis, the diuretic phase of acute tubular necrosis, chronic glomerulonephritis, chronic pyelonephritis, or familial and sporadic renal Mg losses; drug-related causes secondary to diuretics, antibiotic therapy including gentamicin, tobramyocin, ticarcillin, carbenicillin, or amphoteritin B, antineoplastic drugs including cisplatin and cyclosporine; endocrine and metabolic causes including primary and secondary aldosteronism, hyperthyroidism, excessive lactation, pregnancy, hypercalcemia, primary hyperparathyroidism, uncontrolled diabetes mellitus with glucosuria, and acute intermittent porphyria; and congenital causes including maternal diabetes, maternal hyperparathyroidism, maternal hypothyroidism and exchange transfusions.7’9”0~1’7’7*‘9’20 In light of the multitude of etiologies of hypomagnesemia and its prevalence in hospitalized patients, it is possible that reduced Mg often goes undetected by the unsuspecting physician. The symptoms of hypomagnesemia are as varied as its causes, yet these may often be absent or vague. 9*21 Documented manifestations include: neuromuscular symptoms including tremor, myoclonic jerks, convulsions, Chvostek sign, Trous-

Uric acid metabolism in humans.

U RIG ACID, the end product of purine degradation in humans, gains clinical significance during states of increased production, decreased elimination, or increased renal excretion. Under these conditions urate can be deposited in tissues, or uric acid can precipitate in urine to cause uric acid nephrolithiasis. Disorders associated with abnormal uric acid homeostasis include Lesch-Nyhan syndrome, an inherited enzyme deficiency, gout, renal insufficiency, and increased cellular breakdown as in tumor lysis. This article focuses on the sources, production, and elimination of uric acid in man. Uric acid is a weak acid with a pKal of 5.75 due to a proton loss at position 9. l At the physiologic pH range of human serum, uric acid is a monovalent ion, but in urine, which has a more acidic pH range, it is mostly excreted as the free acid. Thus, when uric acid is deposited in tissues, as seen in tophaceous gout, the deposits are mostly monosodium urate utilizing the most abundant cation, and uric acid renal stones are largely free acid.* Uric acid can also lose a second proton at position 3 with a pKa, of 10.3.3 The solubility of uric acid, like the ionization, is pH-dependent, increasing as the pH and urate formation increase.4 In urine, at a pH of 5 .O, uric acid is soluble to 15 mg/dL and increases with increasing pH to 1,520 mg/dL at a pH of 8.0.5 From this information, it is obvious to see why urine alkalinization is an important therapy to prevent or dissolve uric acid kidney stones. To fully understand the metabolism of uric acid, it is important to begin with the source of uric acid, purines. There are three sources of purines: (1) dietary intake of foods containing purine bases, (2) de novo endogenous synthesis from nonpurine precursors, and (3) salvage of purine bases from endogenous catabolism. The major source of dietary purine is protein. The average diet contains 70 to 100 g/d of proteins.6 Hyperuricemia is induced by a high dietary intake of meats containing nucleic acid and mononucleotides.7.8 Zollner reported the intestinal absorption of mononucleotides to be complete, and the absorption of ribonucleotides to be only

Atmospheric weathering caused by dry deposition of acidic compounds

The study was conducted to investigate the effects of deposition on galvanized steel and painted panels using mobile covering/deionized spray devices at exposure sites located at Steubenville, OH and Research Triangle Park (RTP), NC. Ambient rain and deionized spray runoff samples from the panels were collected on an event basis for seven months and underwent detailed chemical analysis. The analysis indicated that the dry deposition of acid gases at the sites increased the dissolution rate of galvanized steel corrosion products. Although the average SO2 level in Steubenville was ten times the RTP value, the rate of Zn dissolution was only 1.9. This result in conjunction with the presence of large amounts of Ca in the Steubenville runoff samples suggest that neutralization of acidic gases by dry deposited basic particulates may be important at the Steubenville site. At the RTP site low levels of anions were found in the runoff from the painted panel with H(1+) as the most abundant cation. This result is consistent with the lack of reactivity towards acidic gases due to the absence of alkaline paint components.

Physiology of magnesium metabolism and the important role of magnesium in potassium deficiency

Magnesium, the second most abundant intracellular cation, has several critically important roles in the body. In addition to energy production and maintaining electrolyte balance, magnesium is essential for normal neuromuscular function as well as calcium and potassium transport. Evidence suggests that a deficit of magnesium is closely interrelated to potassium deficiency and refractory potassium repletion. Although the consequences of hypokalemia are widely documented and recognized, it is only recently that the importance of magnesium deficiency as a cause of potassium depletion has gained clinical attention. Because of the association between hypokalemia and ventricular ectopy/sudden death, familiarity with the causes of magnesium loss, as well as enhanced identification and treatment, appear to be important.

Magnesium metabolism in health and disease.

Magnesium is an important element for health and disease. Magnesium, the second most abundant intracellular cation, has been identified as a cofactor in over 300 enzymatic reactions involving energy metabolism and protein and nucleic acid synthesis. Approximately half of the total magnesium in the body is present in soft tissue, and the other half in bone. Less than 1% of the total body magnesium is present in blood. Nonetheless, the majority of our experimental information comes from determination of magnesium in serum and red blood cells. At present, we have little information about equilibrium among and state of magnesium within body pools. Magnesium is absorbed uniformly from the small intestine and the serum concentration controlled by excretion from the kidney. The clinical laboratory evaluation of magnesium status is primarily limited to the serum magnesium concentration, 24-hour urinary excretion, and percent retention following parenteral magnesium. However, results for these tests do not necessarily correlate with intracellular magnesium. Thus, there is no readily available test to determine intracellular/total body magnesium status. Magnesium deficiency may cause weakness, tremors, seizures, cardiac arrhythmias, hypokalemia, and hypocalcemia. The causes of hypomagnesemia are reduced intake (poor nutrition or IV fluids without magnesium), reduced absorption (chronic diarrhea, malabsorption, or bypass/resection of bowel), redistribution (exchange transfusion or acute pancreatitis), and increased excretion (medication, alcoholism, diabetes mellitus, renal tubular disorders, hypercalcemia, hyperthyroidism, aldosteronism, stress, or excessive lactation). A large segment of the U.S. population may have an inadequate intake of magnesium and may have a chronic latent magnesium deficiency that has been linked to atherosclerosis, myocardial infarction, hypertension, cancer, kidney stones, premenstrual syndrome, and psychiatric disorders. Hypermagnesemia is primarily seen in acute and chronic renal failure, and is treated effectively by dialysis.