Calcium Concentration In Water Research Articles

Transcriptome profiling of the gills of a euryhaline teleost fish, Tetraodon nigroviridis, in response to altered calcium concentrations in water

Transcriptome profiling of the gills of a euryhaline teleost fish, Tetraodon nigroviridis, in response to altered calcium concentrations in water

Modeling deterioration of cementitious materials exposed to calcium leaching in non-isothermal conditions

The paper presents a new mathematical model of hydro-thermo-chemo-mechanical behavior of cementitious materials exposed to contact with the deionized water. For analyzing the calcium leaching process, an equation describing kinetics of the process is used instead of an equilibrium curve commonly used in previous isothermal models. This allows taking directly into account the temperature dependence of characteristic times of calcium leaching from different components of concrete what affects the process kinetics, especially that with a relatively fast decrease of the concentration of calcium in pore water. Constitutive relationships describing the transport and strength properties of concrete during chemical degradation at non-isothermal conditions are discussed. The governing equations of the model and boundary conditions are expressed in terms of the state variables: gas pressure, capillary pressure, temperature, calcium concentration and displacement vector. Numerical solution of the model equations with the Finite Element Method, as well as several examples of application of the model for analysis of some test problems, are presented.

Effect of combined photoperiod, water calcium concentration and pH on survival, growth, and moulting of juvenile crayfish (Procambarus clarkii ) cultured under laboratory conditions

The red swamp crayfish, Procambarus clarkii (Girard), is one of the most commonly farmed freshwater species in inland China due to its high market value and consumer demand. The aim of this study was to determine the optimum combinations of photoperiod, water calcium concentration and pH for juvenile survival, growth and moulting. In our orthogonal experiment, the three environmental factors were varied at three levels (photoperiod: 16L:8D, 12L:12D and 8L:16D; calcium concentration: 45.5, 65.5 and 85.5 mg L−1; and pH: 6.8, 7.8 and 8.8). Range analysis showed that the maximum survival of juvenile crayfish occurred at photoperiods of 16L:8D or 8L:16D, water calcium concentration of 45.5 mg L−1 and pH of 7.8; maximum weight gain at photoperiod 16L:8D, water calcium concentration 65.5 mg L−1 and pH 7.8; maximum length increase at photoperiod 16L:8D, water calcium concentration 65.5 mg L−1 and pH 7.8; and the highest moult frequency at photoperiod 12L:12D, water calcium concentration 65.5 mg L−1 and pH 7.8. Analysis of variance indicated that photoperiod, water calcium concentration and pH significantly influenced only the weight gain of juvenile crayfish (P<0.05). Taking growth into consideration, we suggest that a photoperiod of 16L:8D, calcium concentration of 65.5 mg L−1 and pH 7.8 might be optimal conditions for rearing juvenile P. clarkii.

Associations Between Nondietary Factors and Dairy Herd Performance

Forty-seven dairy herds (approximately 3,129 lactating cows) from northeast of Spain that were offering exactly the same lactating ration were surveyed to determine the effect of nondietary factors on herd performance. The survey collected information on the profile of the owners (their future intentions, the number of workers, and time devoted to the enterprise), information regarding the animals (reproductive performance, incidence of pathology, culling rate, etc.), information on the facilities (number of feeders, waters, stalls, cleanliness, etc.) and information on management practices (numbers of daily milkings, feed deliveries, feed push-ups, cleaning frequency, etc.). In addition, the chemical quality of drinking water from each dairy enterprise was determined. Also, amount of feed delivered to each herd, daily total milk production, and milk quality were obtained for each herd for a period of 8 mo before the fulfillment of the survey. Mortality rate of calves tended to be lesser in herds that weaned progressively than in those that weaned abruptly. Age at first calving was negatively correlated with level of milk production (mainly due to the type of heifer rearing system used). Culling rate tended to be lower in herds that used a close-up ration than in those that did not. Using gloves and paper towels (instead of cloth towels) tended to reduce the somatic cell count in milk. Concentration of calcium in the drinking water tended to be negatively correlated with the number of days open and with the proportion of cows culled due to infertility problems. Despite that the 47 herds fed the same ration and shared a similar genetic base, average milk production per cow ranged from 20.6 to 33.8 kg/d. A positive relationship (r = 0.57) between the number of stalls per cow and milk production was found. The most important nondietary factors that affected milk production in these dairy herds were age at first calving, presence or absence of feed refusals, number of free stalls per lactating cow, and whether feed was pushed up in the feed bunk. These factors accounted for more than 50% of the observed variation, not attributable to the diet, in milk yield.

Modeling of cementitious materials exposed to isothermal calcium leaching, considering process kinetics and advective water flow. Part 1: Theoretical model

Part 1 of the paper presents a new mathematical model of hydro-chemo-mechanical behavior of cementitious materials exposed to contact with the deionized water. For analyzing the calcium leaching process, an equation describing kinetics of the process is proposed instead of an equilibrium curve commonly used in previous models. This allows taking directly into account the characteristic time of calcium leaching which affects the time evolution of the process, especially that with a relatively fast decrease of the concentration of calcium in pore water. Constitutive relationships describing the transport and strength properties of concrete during chemical degradation are discussed. They are expressed in terms of the leaching degree, an internal variable of the model describing the material decalcification. The governing equations of the model and boundary conditions are expressed in terms of the state variables: gas pressure, capillary pressure, calcium concentration and displacement vector. Numerical solution of the model equations with the finite element method, as well as several examples of application of the model for analysis of various problems, are presented in the part 2 paper.

Estimating calcium weathering rates and future lake calcium concentrations in the Muskoka–Haliburton region of Ontario

Calcium (Ca) concentrations in surface waters on the Precambrian Shield are determined primarily by the Ca weathering rate in soil, which requires extensive soil data that generally do not exist. From a water chemistry database comprising approximately 550 lakes in south-central Ontario, Canada, 130 lakes were selected with low Ca concentrations (Ca &lt; 75 µmol·L–1). Calcium weathering is primarily dominated by silicate minerals such as plagioclase and hornblende, allowing the use of Ca–sodium (Na) ratios in lake water to estimate Ca weathering rates. Soil profile data at seven sites indicated that the Ca–Na ratio from mineral weathering is 0.86; correspondingly, Ca weathering rates in lakes ranged from 0.04 to 0.24 kmol·ha–1·year–1 (median of 0.09 kmol·ha–1·year–1). This compares with a range of 0.06–0.24 kmol·ha–1·year–1 (median of 0.14 kmol·ha–1·year–1) obtained using the steady-state water chemistry model. Using these methods to bound potential weathering rates, Ca concentrations in individual lakes at steady state are predicted to decline by 10%–40% compared with current values. Dynamic soil hydrochemical model predictions indicate that Ca concentrations in lakes will be considerably lower than these steady-state predictions within decades if timber harvesting occurs in the drainage basins.

Qualitative and quantitative changes of diatoms with relation to physiochemical water parameters in the littoral zone of the urban Lake Jeziorak Mały

Abstract Phytoplankton in the littoral zone of the urban Lake Jeziorak Mały (Mazurian Lakeland) were studied between April and October of 2002 and 2003. Five diatom species (Fragilaria delicatissima, Aulacoseira granulata, Fragilaria capucina, Diatoma vulgaris, Fragilaria crotonensis) and one genus (Rhizosolenia sp.), comprising the major proportion of total abundance and biomass of diatoms, were chosen for the study. The relationships between the biomass of these diatoms and water temperature, oxygen content, electrolytic conductivity, orthophosphates, silicon and calcium concentrations were analyzed. The biomass of species F. delicatissima, A. granulata and F. capucina tended to be the highest of the six, which were also associated with the widest temperature range, 10.0°C to 18.7°C. These three species exhibited maximum biomass at the highest orthophosphate concentrations. By contrast, F. crotonensis developed in the narrowest water temperature range, 10.0°C to 13.7°C. The maximum biomass of this species was noted at high silicon and calcium concentrations. The diatoms (except F. capucina and Rhizosolenia sp.) contributed to statistically significant observed reductions in nutrient concentrations during their growth. These results indicate that a range of factors is involved in the productivity and limitation of the studied diatoms, with water temperature being of particular importance.

Centrifugal Microfluidics with Integrated Sensing Microdome Optodes for Multiion Detection

An array of four sensing microdome optodes (potassium, sodium, calcium, and chloride) was incorporated into a centrifugal microfluidics platform to obtain a multiion analysis system. The behavior of each sensing microdome was in good agreement with a theoretical model describing the response. The selectivity of each optode over common interfering ions was established and was used to identify calibrant solutions that can be employed for the simultaneous calibration of all four optodes without significant cross-interference. The microfluidic platform was designed to facilitate both three-point calibration of the optodes and triplicate analysis of a sample within a single run, which increases the accuracy of the determination. The optimized microfluidic system was used to determine simultaneously the concentration of potassium, sodium, calcium, and chloride in aquarium water (with the composition of Lake Tanganyika water) with less than 6% error. The simple process of fabrication of these microdomes and their incorporation into a centrifugal microfluidic platform should facilitate the development of portable ion-sensing analysis systems.

Effect of pH on the Taste of Alkaline Electrolyzed Water

The pH dependence of the taste of alkaline electrolyzed water (AEW) made by electrolyzing bottled mineral waters was examined by sensory evaluation. For water with a calcium concentration of 79 or 93 mg/L, the taste of AEW with a pH of 9.5 was considered better than that of the unelectrolyzed water. In contrast, for water with a calcium concentration of 10 mg/L, the taste of the unelectrolyzed water was preferred to that of AEW with a pH of 9.5. Electrolysis reduced the calcium concentrations in waters with calcium concentrations of 79 or 93 mg/L, but did not change the calcium concentration in water with a calcium concentration of 10 mg/L. Electrolysis probably improved the taste of water with a higher calcium concentration by reducing the calcium concentration; however, the effect of electrolysis on water with a calcium concentration of 10 mg/L is likely to be the result of the pH increase alone.

How Much Calcium is in your Drinking Water? A Survey of Calcium Concentrations in Bottled and Tap Water and Their Significance for Medical Treatment and Drug Administration

Different forms of water vary in calcium content. High divalent ion (i.e., Ca(2+), Mg(2+), etc.) concentration is deleterious to the absorption and efficacy of the bisphosphonate group of drugs in osteoporosis treatment. Water with high calcium concentration may also present an alternate pathway of calcium administration. In either case, knowing the actual concentration is critical. The current paper is a surveillance study. We hypothesize that there is considerable variation in the calcium concentrations in the various water sources: tap water from US and Canadian cities of different regions and purified, spring, and mineral bottled waters. In addition, we hypothesize that the water filter removes a significant amount of minerals including calcium from the water. Calcium concentrations in various city tap waters, as well as an assorted number of bottled waters, were determined through the direct inspection of scientific data. The effect of filtering was also determined by mineral analysis of mineral water directly before and after filtration. The calcium concentration of water varies from 1 to 135 mg/L across the USA and Canada. Most spring waters were found to have a relatively low calcium concentration, with an average of 21.8 mg/L. Purified waters contain a negligible calcium concentration. Mineral waters, on the other hand, were generally found to contain higher calcium concentrations, an average of 208 mg/L of calcium. Filtration was found to remove a considerable amount of calcium from the water, removing 89% on average. Calcium concentration in water varied substantially from different sources in the USA and Canada. Bottled waters presented with concentrations of calcium covering a very large range. Certain tap and bottled waters present with concentrations of calcium sufficient to exhibit a deleterious effect on bisphosphonate treatment. Alternatively, certain waters may be used as a source of calcium that may provide over 40% of the recommended daily intake for calcium.

Comparison of Glyphosate Salts (Isopropylamine, Diammonium, and Potassium) and Calcium and Magnesium Concentrations on the Control of Various Weeds

Greenhouse and field experiments were conducted near Knoxville, TN, during 2002 and 2003 to investigate the effects of calcium and magnesium ions on the performance of three glyphosate formulations with and without diammonium sulfate (AMS). Weed species investigated in the greenhouse were broadleaf signalgrass, pitted morningglory, Palmer amaranth, and yellow nutsedge. Three glyphosate formulations (isopropylamine salt, diammonium salt, and potassium salt) and two glyphosate application rates (0.42 and 0.84 kg ae/ha) were applied to weeds in water fortified with either calcium or magnesium at concentrations of 0, 250, 500, 750, and 1,000 ppm. In all comparisons, there were no differences in the three glyphosate formulations. Glyphosate activity was reduced only when cation concentration was &gt;250 ppm, and this antagonism was not observed when 2% w/ w AMS was added to the spray solution. A chemical analysis of the calcium and magnesium concentrations in water collected from farmers indicated that water samples from eight different producers contained relatively low amounts of cations, with calcium at &lt;40 ppm and magnesium at &lt;8 ppm. In the field results using these and other waters as the herbicide carrier, broadleaf signalgrass control was greater with the 0.84 kg ae/ha than 0.42 kg ae/ha glyphosate rate regardless of water source or addition of AMS. Pitted morningglory responded similarly to glyphosate with water from all farms and with AMS added, and the addition of AMS gave similar results for both glyphosate rates. In 2003, common cocklebur was evaluated and control was &gt;93% regardless of glyphosate rate, water source, or AMS addition. Based on these results, the addition of AMS-based adjuvants to many glyphosate applications may not be warranted.

Predicting Gran alkalinity and calcium concentrations in river waters over a national scale using a novel modification to the G-BASH model

Monthly stream water calcium and Gran alkalinity concentration data from 11 sub-catchments of the Nether Beck in the English Lake District have been used to appraise the transferability of the Scottish, River Dee-based G-BASH model. Readily available riparian zone geochemistry and flow paths were used initially to predict minimum and mean stream water concentrations at the Nether Beck, based on calibration equations from the River Dee catchment data. Predicted values significantly exceeded observed values. Differences in runoff between the two areas, leading to a dilution effect in the Nether Beck, explained most of the difference between observed and predicted values. Greater acid deposition in the Lake District also reduced stream water Gran alkalinity concentrations in that area. If regional differences in precipitation, evapotranspiration and pollutant deposition are incorporated into the model, it may then be used reliably to predict catchment susceptibility to acidification over a wide regional (national) scale.

Relationship between alternation of cerebral blood flow and formation of brain edema around the hematoma after experimental intracerebral hemorrhage

Objective To investigate the mechanism of brain edema formation around the hematoma and the relationship between the formation of brain edema and the changes of regional cerebral blood flow after intracerebral hemorrhage (ICH) in rats, and to provide experimental basis for the clinical treatment of ICH . Methods Seventy male Sprague-Dawley rats were randomly divided into ICH groups and sham-operated groups. ICH was produced by microinjection of 40 ul fresh autologous blood or saline into the right caudatum. Dynamic CT perfusion imaging was performed, and the parameters of regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), and mean transit time (MTT) around the hematoma were calculated respectively. Then the rats were sacrificed, and the water content, sodium, potassium, and calcium concentrations were measured respectively. The correlative study between the water content and rCBF and rCBV were carried out. Results The gradient of perihematomal hypoperfusion was revealed on CT perfusion maps in ICH groups. The alternation of rCBF around the hematomas were fluctuated, and rCBF reduction was most pronounced at 1 hour afer ICH, then the rCBF gradually returned, reaching the peaks at 6 hours and 24 hours after ICH, respectively. In the meantime, rCBV reduction around the hematoma was most pronounced at 1 hour after ICH. Then the rCBV gradually increased, and reaching the peak at 24 hours. The water contents were gradually increased in the ipsilateral basal ganglia in the animals sacrificed at 6, 24, and 72 hours. The accumulation of water was at its peak at 24 hours, and remained in the animals sacrificed at the 72 hours. The perihemorrhagic water contents correlated significantly with rCBV surrounding hematomas, r=0.372(one-tailed), P0.05. Conclusion The perihemorrhagic brain edema results from the common effects of the blood-brain-barrier disruption, cytotoxic edema, and the accumulation of osmotically active substances. The rCBF reduction occured in the early stage of ICH and the rCBV compensatory increase play important roles in producing vasogenic edema. Perfusion CT and its parameter analysis is a suitable method in the study of the relationship between the formation of brain edema and the changes of regional cerebral blood flow after intracerebral hemorrhage in vivo.

The Disruption of Daphnia magna Sodium Metabolism by Humic Substances: Mechanism of Action and Effect of Humic Substance Source

Humic substances have important functions in aquatic systems. While these roles are primarily indirect, influencing the physicochemical environment, recent evidence suggests these materials may also have direct biological actions. This study investigated the mechanism by which humic substances perturb sodium metabolism in a freshwater invertebrate, the water flea Daphnia magna. Aldrich humic acid (AHA) stimulated the maximal rate of whole-body sodium influx (Jmax) when experimental pH was 6 and water calcium content was 0.5 mM. This effect persisted at pH 8 and 1 mM calcium but not at pH 8 in the absence of calcium. An indirect action of AHA on apical transporter activity was proposed to explain this effect. At pH 4 AHA promoted a linear sodium uptake kinetic relationship, attributed to altered membrane permeability due to enhanced membrane binding of humic substances at low pH. In contrast, a real-world natural organic matter sample had no consistent action on sodium influx, suggesting that impacts on sodium metabolism may be limited to commercially available humic materials. These findings question the applicability of commercially available humic substances for laboratory investigations and have significant implications for the study of environmental metal toxicity.

Effects of temperature and water calcium concentration on growth, survival and moulting of freshwater crayfish, Paranephrops zealandicus

Two 3-month experiments were conducted to investigate the effects of temperature and water calcium concentrations on growth, survival and moulting of freshwater crayfish ( Paranephrops zealandicus). Both experiments were conducted using three replicates of five treatments (water temperatures of 14, 16, 18, 20 and 22 °C for Experiment 1 and water calcium concentrations of 0, 5, 10, 30 and 80 mg/L for Experiment 2). Growth rates increased with water temperature (maximum specific growth rate = 0.57) but were unchanged with increased water calcium concentration. Variability in growth rates decreased with increased water calcium concentrations. Survival decreased as water temperatures exceeded 16 °C and increased with water calcium concentrations above 10 mg/L. Inter-moult period decreased from > 90 ± 20 days at water temperatures of 14 °C to ∼ 40 ± 10 days at water temperatures > 20 °C. Moult increment of the crayfish was unaltered by either water temperature or water calcium concentrations. The optimum water temperature for productivity under conditions employed was 16 °C.

Spectrophotometric analysis of the concentration of biogenic and abiogenic elements in water

Literature data on the concentration of certain heavy metals in the earth's ecosphere are compared with the results of measurements of the concentration of antimony, calcium, magnesium, and silicon in the drinking water of the South Ural and certain other regions of Russia. © 2005 Optical Society of America

Dermatitis, branchitis and mortality in empire gudgeon Hypseleotris compressa exposed naturally to runoff from acid sulfate soils

Severe dermatitis and branchitis are described in a wild population of empire gudgeon Hypseleotris compressa, an Australian eleotrid, exposed naturally to runoff from acid sulfate soils (ASS) in a drained estuarine embayment in eastern Australia. After at least 2 d exposure to pH < 4, and up to 7 d exposure to pH < 6, approximately 50% of the fish sampled had moderate to severe diffuse epidermal hyperplasia, usually at scale margins, and scattered areas of moderate to severe, focal to locally extensive, subacute, necrotising dermatitis. Saprolegnia spp. had invaded epidermis in some inflamed areas. In gills, there was moderate to severe hyperplasia and necrosis of secondary lamellar epithelium, with fusion of adjacent secondary lamellae. Inorganic monomeric aluminium and calcium concentrations in water at the site during the event were 27.7 and 16.6 mg l(-1), respectively. Large numbers of empire gudgeons at the study site had died after at least 8 d exposure to pH < 4, and up to 13 d exposure to pH < 6. These findings provide clear evidence that acidification of estuarine systems by runoff from ASS has deleterious effects on aquatic biota. Furthermore, study findings suggest a mechanism whereby lesions of epizootic ulcerative syndrome (EUS) may be initiated in estuarine fishes by a combination of sublethal exposure to ASS runoff and Aphanomyces invadans infection, a suggestion consistent with the geographic and temporal distribution of EUS outbreaks in Australian estuaries.

CHEMISTRY OF COALBED METHANE DISCHARGE WATER INTERACTING WITH SEMI‐ARID EPHEMERAL STREAM CHANNELS1

ABSTRACT: The objective of this study was to examine the chemistry of Coalbed Methane (CBM) discharge water reacting with semi‐arid ephemeral stream channels in the Powder River Basin, Wyoming. The study area consisted of two ephemeral streams: Burger Draw and Sue Draw. These streams are tributaries to the perennial Powder River. Samples were collected bimonthly from three CBM discharge points and seven channel locations in Burger Draw and Sue Draw. Samples were also collected bimonthly from the Powder River above and below the confluence of Burger Draw. Before sample collection, the pH and electrical conductivity (EC) were measured in the field. Samples were transported to the laboratory and analyzed for alkalinity, major cations, and anions. From the measurement of sodium (Na), calcium (Ca), and magnesium (Mg), practical sodium adsorption ratio (SARp) and true sodium adsorption ratio (SARt) were calculated. Results suggest pH and EC of CBM discharge water was 7.1 and 4.3 dS/m, respectively. The CBM discharge water consisted of higher concentrations of sodium and alkalinity compared to other components. The pH of CBM discharge water increased significantly (p = 0.000) in the downstream channel of Burger Draw from 7.1 to 8.84 before it joined with the Powder River. Dissolved calcium concentration of CBM discharge water decreased significantly (p = 0.000) in the downstream channel water. Subsequently, SARp increased approximately from 24 to 29. The SARt also increased significantly (p = 0.001) in the downstream channel water. For instance, SARt of CBM discharge water increased from 32.93 to 45.5 downstream channels after the confluence of Sue Draw with the Burger Draw. The only significant difference in water chemistry above and below the confluence of Burger Draw with the Powder River was pH, which increased from 8.36 to 8.52. The significant increase in SAR values of CBM discharge water in Burger Draw and Sue Draw tributaries suggest a careful monitoring of salinity and sodicity is needed if CBM discharge water is used for irrigation in semi‐arid environments. Results discussed in this study will be useful to downstream water users who depend on water for irrigation.

Prescribed fire, soils, and stream water chemistry in a watershed in the Lake Tahoe Basin, California

Before Euro-American settlement fire was a common process in the forests of the Lake Tahoe Basin. The combination of drought, fire suppression, and past harvesting has produced ecosystems that are susceptible to high-severity wildfires. Consequently, a program of prescribed fire has been recommended but there is incomplete understanding of the ecological effects of fuels treatments, especially with regard to how treatments will affect the flow of nutrients to Lake Tahoe. Nitrogen and phosphorus are the most important nutrients affecting algal growth, and thus lake clarity. Existing data demonstrate a long-term shift from a co-limitation by both nitrogen and phosphorus to phosphorus limitation. Two high-consumption, moderate-intensity prescribed fires were conducted to determine their effects on soil and stream water chemistry. Stream water calcium concentrations increased in burned watersheds whereas soluble reactive phosphorus concentrations were not significantly different. Prescribed fires released calcium and raised soil pH and this may have resulted in the incorporation of phosphorus into insoluble forms. Stream monitoring data indicates water quality effects last for ~3 months. Prescribed fires did not significantly increase the amount of soluble reactive phosphorus in stream waters. However, additional research is needed to determine if prescribed fire increases erosion or movement of particulate P, particularly in areas with steep slopes.

Humic substances and the water calcium content change the toxicity of malachite green

Summary Laboratory experiments were conducted to test interactive effects of calcium(Ca 2+ ) content and the presence of humic substance (HS) on malachite green (MAG)-induced toxicity in fish embryos and larvae by means of a semistatic 144-hembryo-larval-test with zebrafish (Danio rerio). Two kinds of reconstituted water samples were used to produce the test media by mixing salts into deionized water resulting in either hard water (›Ca ) HS), or soft water (flCa ) HS). By adding HS two additional test media were produced (›Ca + HS, flCa + HS). MAG was tested in concentrations of 0.05, 0.10, 0.15, 0.20, 0.25 mg L )1 . The toxicity ranking of MAG (mg L )1 ) to embryos based on 96-h-LC50 in the different test water samples is: ›Ca ) HS (0.061) > ›Ca + HS (0.123) ¼ flCa ) HS (0.12) ‡fl Ca + HS (0.134) and on 144-h-LC50 to larvae is: ›Ca ) HS (0.038) > ›Ca + HS (0.06) > flCa ) HS (0.077) ¼ flCa + HS (0.077). Mortality of all the groups was significantly different (P < 0.05). Increased Ca 2+ concentrations did not protect zebrafish embryos and larvae from MAG-induced toxicity. At high Ca 2+ conditions, the mortality of the embryos as well as of the larvae is reduced in the ›Ca + HS group relative to the ›Ca ) HS group. Thus, at high Ca 2+ conditions the HS does affect the MAG-induced mortality. The mechanism which causes the higher toxicity of MAG in the presence of higher Ca 2+ concentrations is poorly understood. A probable explanation could be the stimulation of the calcium-binding protein calmodulin as well as the calmodulin kinase II in cell membranes in the presence of high Ca 2+ concentrations.