Effect of magnesium supplementation and training on magnesium tissue distribution in rats

The aim of this work is to study the effect of training and Mg supplementation on body pools of Mg and on Mg tissue distribution. Forty male Wistar rats were divided into four groups (n=10): control group (C); trained group (T); Mg-supplemented group (+Mg); and trained and Mg-supplemented group (+MgT). The Mg supplement (100 ppm of Mg) was given in the drinking water for 21 d. The training consisted of swimming during 60% of maximal swimming time obtained in the first session to exhaustion, during 3 wk (5 d a week). The variables measured were: erythrocytes (RBC), hemoglobin (Hb), hematocrit (Hto), total proteins (TP), and Mg in serum, RBC, liver, muscle, bone, and kidney. There was less Mg in liver, muscle, and erythrocyte in trained animals than in control or supplemented animals (T vs C, +MgT vs C and +MgT vs +Mg) (p < 0.01). Trained antimals (T and +MgT) showed higher Mg kidney rates than the untrained ones (p<0.01). There was less bone Mg in control (C) and in supplemented and trained (+MgT) groups than in trained (T) and in supplemented (+Mg) animals (p<0.01). Serum Mg showed a decreasing concentration profile in the following order: +Mg, +MgT, T, C (p<0.01). We conclude that Mg supplementation improves bone and serum Mg levels, but this does not affect Mg status in soft tissues. Maintained exercise leads to a diminution of Mg in the aforementioned soft tissues that is not noticeable in serum, probably provoked by an increase of renal excretion.     

Cooperative phenomena in the membrane potential of parathyroid cells induced by divalent cations

Membrane potentials of mouse parathyroid cells were measured by means of the intracellular microelectrode method. The membrane potential in external Krebs solution containing 2.5 mM of Ca++ was -23.6 +/- 0.4 mV (mean +/- standard error of mean). The low concentration of Ca++ (1.0 mM) caused hyperpolarization of the membrane potential to -61.7 +/- 0.8 mV. The membrane potential was proportional to the logarithm of the concentration of K ion in the solution of low Ca ion. The concentration of external Na+, C1- and HPO4-- had no effect on the membrane potential. The sigmoidal transition of membrane potentials was induced by the change of Ca ion concentration in the range from 2.5 to 1.0 mM. The change of the membrane potentials in low Ca ion is originated from increase in potassium permeability of the cell membrane. The similar sigmoidal changes of the membrane potentials were observed in the solution containing 4 to 3 mM of Sr ion. The Mg and Ba ion showed smaller effect on the membrane potential. The Goldman equation was extended to divalent ions. Appling the extended membrane potential equation, ratios of the permeability coefficients were obtained as follows: PK/PCa = 0.067 for 2.5 mM Ca++, 0.33 for 1.0 mM Ca++; PK/PSr = 0.08 for 4 mM Sr++ and 0.4 for 3 mM Sr++; PK/PMg = 0.5; PK/PBa = 0.67 for all range of concentration. The Hill constants of Sr ion and Ca ion were 20; the relationship between Sr ion and Ca ion was competitive. The Hill constants of Mg and Ba ion were 1 each. The Hill constant of Ca ion was depend of the temperature; nmax = 20 at 36 degrees C, n = 9 at 27 degrees C, n = 2 at 22 degrees C. The enthalpy of Ca-binding reaction was obtained from the Van't Hoff plot as 0.58 kcal. The activation energies of the K+ permeability increase were obtained from the Arrhenius plots as 3.3 kcal and 4 kcal. The difference, 0.7 kcal, corresponds to the enthalpy change of this reaction, of which value is close to that of the Ca-binding reaction.     

Effects of Aluminum Exposure on Bone Mineral Density,Mineral, and Trace Elements in Rats

The purpose of the study was to investigate the effects of aluminum (Al) exposure on bone mineral elements, trace elements, and bone mineral density (BMD) in rats. One hundred Wistar rats were divided randomly into two groups. Experimental rats were given drinking water containing aluminum chloride (AlCl₃, 430 mg Al³⁺/L), whereas control rats were given distilled water for up to 150 days. Ten rats were sacrificed in each group every 30 days. The levels of Al, calcium (Ca), phosphorus (P), magnesium (Mg), zinc (Zn), iron (Fe), copper (Cu), manganese (Mn), selenium (Se), boron (B), and strontium (Sr) in bone and the BMD of femur were measured. Al-treated rats showed lower deposition of Ca, P, and Mg compared with control rats. Levels of trace elements (Zn, Fe, Cu, Mn, Se, B, and Sr) were significantly lower in the Al-treated group than in the control group from day 60, and the BMD of the femur metaphysis in the Al-treated group was significantly lower than in the control group on days 120 and 150. These findings indicate that long-term Al exposure reduces the levels of mineral and trace elements in bone. As a result, bone loss was induced (particularly in cancellous bone).     

The effect of ascorbic acid supplementation on sperm quality, lipid peroxidation and testosterone levels of male Wistar rats

This study was conducted to investigate the effects of ascorbic acid supplementation in drinking water on semen quality, lipid peroxidation and plasma testosterone level of male rats. In this investigation, 24 male Wistar rats were used. The animals were divided into three group, and 500, 250 and 0 (control) mg/kg/day ascorbic acid were supplemented with drinking water of rats in Groups A, B and C during 8 weeks, respectively. Ascorbic acid supplementation did not increase in the body weight and weights of the testis, epididymis, seminal vesicles and ventral prostate. Exogenous supplementation with ascorbic acid significantly increased (P<0.05) the concentration of ascorbic acid in the testes and blood plasma, and the level of lipid peroxidation significantly decreased (P<0.05) in these locations. There was no significant difference in spermatozoon motility among the three groups. However, epididymal sperm concentration and plasma testosterone level significantly increased (P<0.05) in the ascorbic acid treated animals when compared to the control animals. The results suggest that ascorbic acid supplementation improves reproductive traits of male rats that are associated with high fertility.     

The effect of thyroparathyroidectomy, parathyroid hormone and calcitonin on plasma strontium in rats

The effect of thyroparathyroidectomy (TPTX) on the plasmatic Sr concentrations in rats previously supplemented with this element, has been studied, as well as its effect on the treatment of TPTX rats with hormonal combinations and, finally, the one presenting hormonal excess or defect of the phosphocalcium metabolism regulating hormones: parathormone (PTH) and calcitonin (CT). Twenty four hours after TPTX, the plasmatic Sr concentrations show a pattern similar to those of Ca and Mg and contrary to Pi. The subsequent evolution is different, as the plasmatic concentrations increase, probably due to the maintenance of Sr supplementation. The administration of this element to TPTX rats and the treatment with a hormonal combination with two of the following hormones: PTH, CT and T4 antagonize the hormonal effect on the restoration of the plasmatic concentrations of the elements analyzed. The PTH excess and defect (TPTX treated with CT + T4) show plasmatic increases in Sr; the CT excess provokes decreases while the defect (administration of PTH + T4) causes increases. The T4 administration reproduces the CT effects, but inconsistently. These results suggest that CT may be the hormone that plays a regulating role in the plasmatic Sr concentrations.     

Examining water temperature proxies in<Emphasis Type="Italic"> Porites</Emphasis> corals from the Great Barrier Reef: a cross-shelf comparison

Cores from colonies of the coral species Porites sp. were collected from inshore, mid-shelf, and outer reef localities (central Great Barrier Reef) to test the robustness of the major elemental sea surface temperature (SST) proxies (B/Ca, Mg/Ca, Sr/Ca, U/Ca) to the influence of inshore processes. Time series analyses of Sr/Ca, U/Ca, B/Ca, and Mg/Ca are compared to sea surface temperature (SST) in order to provide calibrations for these elements. This study shows that there are significant variations between the corals with respect to some of the proxies. In some cases, variations of ~6 °C are observed for a single U/Ca value. This magnitude of variation is also seen in the Mg/Ca proxy and, to a smaller extent, in the B/Ca–SST relationship. In two of the corals, both Mg/Ca and U/Ca do not follow a seasonal signal. The Mg/Ca and U/Ca ratios for two inshore corals are significantly different than the offshore corals (lower and higher, respectively). The other two proxies (B/Ca and Sr/Ca) do not display any inshore vs. offshore variations except for one inshore site that did not have a clear seasonal signal for either of these proxies. The Sr/Ca–SST relationship is the most robust, with a temperature variation of ~2 °C for a single Sr/Ca value, which is within error for this technique.     

硒对心肌质膜(Ca~(2+)·Mg~(2+))-ATPase和肌浆网Ca~(2+)-ATPase活力的影响

本文以豚鼠和大白鼠心肌肌浆网膜(SR)Ca~(2+)-ATPase的活力,心肌质膜(SL)(Ca~(2+)Mg~(2+))-ATPase的活力和电子显微镜的方法探索克山病病区粮中低硒与心肌细胞钙转运调控的共系,实验结果为硒对克山病有预防作用的观点提供了新的理论依据,并进一步支持了“克山病是一种心肌线粒体病”的观点。     

Effect of long-term administration of arsenic (III) and bromine with and without selenium and iodine supplementation on the element level in the thyroid of rat

The aim of this study was to evaluate the influence of arsenic and bromine exposure with or without iodine and selenium supplementation on the element level in the thyroid of rats. Four major groups of Wistar female rats were fed with respective diets: group A - standard diet, group B - iodine rich diet (10 mg I/kg food), group C - selenium rich diet (1 mg Se/kg) and group D - iodine and selenium rich diet (as in group B and C). Each group was divided into four subgroups per 7 animals each receiving either NaAsO(2) ip (6.5 mg.kg(-1) twice a week for two weeks and 3.25 mg.kg(-1) for six weeks) or KBr in drinking water (58.8 mg.l(-1)) for 8 weeks or combined administration of both substances. Remaining subgroup served as controls. After 8 weeks thyroid glands were analyzed by ICP-MS for As, Br, Se, and I content. The exposition of rat to arsenic or bromine causes the accumulation of these elements in the thyroid gland ( approximately 18 ppm of As, approximately 90 ppm of Br) and significantly affects iodine and selenium concentration in the thyroid. In iodine and/or selenium supplemented rats the bromine intake into the thyroid was lowered to approximately 50% of the level in unsupplemented animals. Also selenium thyroid level elevated due to KBr administration was lowered by iodine supplementation in the diet. The accumulation of arsenic in the thyroid was not influenced by selenium or iodine supplementation; however, As(III) administration increased iodine thyroid level and suppressed selenium thyroid level in selenium or iodine supplemented group of animals.     

Ionic regulation of adenylate cyclase from the cilia of Paramecium tetraurelia.

The kinetics of the ionic regulation of an adenylate cyclase associated with the excitable ciliary membrane from Paramecium tetraurelia was examined. Glycerol (30%, v/v) stabilized the enzyme, and activated by an increase in Vmax. (3-fold) and a decrease in the apparent Km for MgATP (6-fold). Kinetic analysis of Mg2+ effects showed a stimulation via a single metal-binding site separate from the substrate site, with a dissociation constant, Ks, of 0.27 mM. Analysis of Ca2+ effects showed (i) an uncompetitive inhibition with respect to substrate MgATP, and (ii) dependence of the extent of inhibition on the free Mg2+ concentration. Ki values ranged from 4 to 130 microM-Ca2+ in the presence of 0.55-2 mM-Mg2+ respectively. This indicates competition between Mg2+ and Ca2+ at the metal-binding site. The Ca2+ effect was specific; Sr2+ and Ba2+ were almost without effect, and 100 microM-Ba2+ did not interfere with the Ca2+ inhibition. The actions of Ca2+ were readily reversible after addition of EGTA. K+ activated the adenylate cyclase at concentrations around 20 mM. The stimulatory potency of K+ was dependent on the free Mg2+ concentration. At 1 mM free Mg2+, 20 mM-K+ doubled the adenylate cyclase activity. The inhibitory Ca2+ and stimulatory K+ inputs were independent of each other.     

Spondias mombin supplementation attenuated cardiac remodelling process induced by tobacco smoke

The objective of this study was to investigate the influence of Spondias mombin (SM) supplementation on the cardiac remodelling process induced by exposure to tobacco smoke (ETS) in rats. Male Wistar rats were divided into 4 groups: group C (control, n = 20) comprised animals not exposed to cigarette smoke and received standard chow; group ETS (n = 20) comprised animals exposed to cigarette smoke and received standard chow; group ETS100 (n = 20) received standard chow supplemented with 100 mg/kg body weight/d of SM; and group ETS250 (n = 20) received standard chow supplemented with 250 mg/kg body weight/d of SM. The observation period was 2 months. The ETS animals had higher values of left cardiac chamber diameters and of left ventricular mass index. SM supplementation attenuated these changes. In addition, the myocyte cross‐sectional area (CSA) was lower in group C compared with the ETS groups; however, the ETS250 group had lower values of CSA compared with the ETS group. The ETS group also showed higher cardiac levels of lipid hydroperoxide (LH) compared with group C; and, groups ETS100 and ETS250 had lower concentrations of LH compared with the ETS group. Regarding energy metabolism, SM supplementation decreased glycolysis and increased the β‐oxidation and the oxidative phosphorylation. There were no differences in the expression of Nrf‐2, SIRT‐1, NF‐κB, interferon‐gamma and interleukin 10. In conclusion, our results suggest that ETS induced the cardiac remodelling process. In addition, SM supplementation attenuated this process, along with oxidative stress reduction and energy metabolism modulation.     

Effects of boron and calcium supplementation on mechanical properties of bone in rats

OBJECTIVE: The objective of this study was to consider the effects of boron (B) and calcium (Ca) supplementation on mechanical properties of bone tissues and mineral content of the selected bones in rats. METHODS: Adult male Sprague Dawley rats underwent three different treatments with boron and calcium in their drinking water, while taking diet ad libitum for 4 weeks. Rats in the three treatment groups received 2 mg B/d, 300 mg Ca/d, and a combination of 2 mg B+ 300 mg Ca/d, respectively. After the experimental period body weights were recorded and bone mechanical properties were determined on the tibiae, femurs, and fifth lumbar vertebral bones and the mineral contents of these bones was calculated as the ash percentage. RESULTS: Better measurement of bone mechanical properties were observed for boron supplementation. The stiffness of the lumbar vertebral bones tended to increase in all groups and was significant for Ca supplementation. The significant maximal load obtained for boron in all bones indicates higher strength and less strength for apparently a high level of calcium, while this negative defect in the case of lumbar vertebral bones was corrected in the presence of boron. Highest mean energy to maximal load was shown with boron supplementation, demonstrating significant values with Ca group, and lower energy for the lumbar vertebral bones in Ca group in comparison with the controls. Less deformation at the yield points was shown in Ca group. There were no significant differences in ash weights among the four groups. CONCLUSIONS: Additional and longer studies are warranted to further determine the effects of supplemental boron with different calcium levels and possibly other minerals involved in bone mechanical properties in rats.     

A Fourier transform infrared spectroscopic study of the interaction of alkaline earth cations with the negatively charged phospholipid 1, 2-dimyristoyl-sn-glycero-3-phosphoglycerol

The interaction of aqueous phospholipid dispersions of negatively charged 1,2-dimyristoyl-sn-glycero-3-phosphoglycerol, sodium salt (DMPG) with the divalent cations Mg(2+), Ca(2+) and Sr(2+) at equimolar ratios in 100 mM NaCl at pH 7 was investigated by Fourier transform infrared spectroscopy. The binding of the three cations induces a crystalline-like gel phase with highly ordered and rigid all-trans acyl chains. These features are observed after storage below room temperature for 24 h. When the gel phase is heated after prolonged incubation at low temperature phase transitions into the liquid crystalline phase are observed at 58 degrees C for the DMPG:Sr(2+), 65 degrees C for the DMPG:Mg(2+), and 80 degrees C for the DMPG:Ca(2+) complex. By subsequent cooling from temperatures above T(m) these complexes retain the features of a liquid crystalline phase with disordered acyl chains until a metastable gel phase is formed at temperatures between 38 and 32 degrees C. This phase is characterized by predominantly all-trans acyl chains, arranged in a loosely packed hexagonal or distorted hexagonal subcell lattice. Reheating the DMPG:Sr(2+) samples after a storage time of 2 h at 4 degrees C results in the transition of the metastable gel to the liquid crystalline phase at 35 degrees C. This phase transition into the liquid crystalline state at 35 degrees C is also observed for the Mg(2+) complex. However, for DMPG:Mg(2+) at higher temperatures, a partial recrystallization of the acyl chains occurs and the high temperature phase transition at 65 degrees C is also detected. In contrast, DMPG:Ca(2+) exhibits only the phase transition at 80 degrees C from the crystalline gel into the fluid state upon reheating. Below 20 degrees C, the rate of conversion from the metastable gel to a thermodynamically stable, crystalline-like gel phase decreases in the order Ca(2+)&z. Gt;Mg(2+)>Sr(2+). This conversion into the crystalline gel phase is accompanied by a complete dehydration of the phosphate groups in DMPG:Mg(2+) and by a reorientation of the polar lipid head groups in DMPG:Ca(2+) and in DMPG:Sr(2+). The primary binding sites of the cations are the PO(2)(-) groups of the phosphodiester moiety. Our infrared spectroscopic results suggest a deep penetration of the divalent cations into the polar head group region of DMPG bilayers, whereby the ester carbonyl groups, located in the interfacial region of the bilayers, are indirectly affected by strong hydrogen bonding of immobilized water molecules. In the liquid crystalline phase, the interaction of all three cations with DMPG is weak, but still observable in the infrared spectra of the DMPG:Ca(2+) complex by a slight ordering effect induced in the acyl chains, when compared to pure DMPG liposomes.     

Inhibition of oxidative phosphorylation by Ca2+ or Sr2+: a competition with Mg2+ for the formation of adenine nucleotide complexes

Intramitochondrial Sr2+, similar to Ca2+, inhibits oxidative phosphorylation in intact rat-liver mitochondria. Both Ca2+ and Sr2+ also inhibit the hydrolytic activity of the ATPase in submitochondrial particles. Half-maximal inhibition of ATPase activity was attained at a concentration of 2.5 mM Ca2+ or 5.0 mM Sr2+ when the concentration of Mg2+ in the medium was 1.0 mM. The inhibition of ATPase activity by both cations was strongly decreased by increasing the Mg2+ concentration in the reaction medium. In addition, kinetical data and the determination of the concentration of MgATP, the substrate of the ATPase, in the presence of different concentrations of Ca2+ or Sr2+ strongly indicate that these cations inhibit ATP hydrolysis by competing with Mg2+ for the formation of MgATP. On the basis of a good agreement between these results with submitochondrial particles and the results of titrations of oxidative phosphorylation with carboxyatractyloside or oligomycin in mitochondria loaded with Sr2+ it can be concluded that intramitochondrial Ca2+ or Sr2+ inhibits oxidative phosphorylation in intact mitochondria by decreasing the availability of adenine nucleotides to both the ADP/ATP carrier and the ATP synthase.     

Energy interconversion in sarcoplasmic reticulum vesicles in the presence of Ca2+ and Sr2+ gradients

Sarcoplasmic reticulum vesicles of rabbit skeletal muscle are able to accumulate Ca2+ or Sr2+ at the expense of ATP hydrolysis. Depending on the conditions used, vesicles loaded with Ca2+ can catalyze either an ATP in equilibrium Pi exchange or the synthesis of ATP from ADP and Pi. Both reactions are impaired in vesicles loaded with Sr2+. The Sr2+ concentration required for half-maximal ATPase activity increases from 2 microM to 60-70 microM when the Mg2+ concentration is raised from 0.5 to 50 mM. The enzyme is phosphorylated by ATP in the presence of Sr2+. The steady state level of phosphoenzyme varies depending on both the Sr2+ and Mg2+ concentrations in the medium. Phosphorylation of the enzyme by Pi is inhibited by both Ca2+ and Sr2+. In the presence of 2 and 20 mM Mg2+, half-maximal inhibition is attained in the presence of 4 and 8 microM Ca2+ or in the presence of 0.24 mM and more than 2 mM Sr2+, respectively. After the addition of Sr2+, the phosphoenzyme is cleaved with two different rate constants, 0.5-1.5 s-1 and 10-18 s-1. The fraction of phosphoenzyme cleaved at a slow rate is smaller the higher the Sr2+ concentration in the medium. Ca2+ inhibition of enzyme phosphorylation by Pi is overcome by the addition of ITP. This is not observed when Ca2+ is replaced by Sr2+.     

Interaction of calcium with bovine plasma protein C

The binding of 45Ca2+ to bovine plasma protein C (PC) and to activated bovine plasma protein C (APC) has been examined by equilibrium ultrafiltration at pH 7.4 and 25 degrees C. Under these conditions, PC possesses 16.0 plus or minus 2.0 equivalent Ca2+ binding sites, of average KD (8.7 plus or minus 1.5) x 10(-4) M, and APC contains 9.0 plus or minus 1.0 equivalent Ca2+ binding sites, with an average KD of (4.3 plus or minus 1.1) x 10(-4) M. Both Mn2+ and Sr2+ were capable of ready displacement of Ca2+ from a Ca2+-PC complex, while Mg2+ was less effective in this regard. The alpha-thrombin-catalyzed activation of PC was inhibited by the presence of Ca2+. A kinetic analysis of this effect demonstrated that it was, in large part, due to an increase in the Km of the reaction. Addition of other divalent cations, e.g. Mn2+, Sr2+, and Mg2+, in place of Ca2+ also resulted in inhibition of the alpha-thrombin-catalyzed activation of PC in a manner which paralleled their ability to displace Ca2+ from a Ca2+-PC complex. On the other hand, the activation of PC by the coagulant protein from Russell's Viper venom was augmented by the presence of Ca2+. Other divalent metal ions, such as Sr2+ and Mn2+, in the absence of Ca2+, also weakly stimulated this reaction. Mg2+ was without notable effect.     

Boron supplementation in peripartum Murrah buffaloes: The effect on calcium homeostasis,bone metabolism,endocrine and antioxidant status

BackgroundCalcium homeostasis and immuno-endocrine system undergoes drastic changes in peripartum dairy animals and failure to adapt these physiological changes causes major impact on animal health as well as productivity. Boron (B), a newer trace element, influences calcium (Ca), phosphorus (P) and magnesium (Mg) metabolism as well as immune system by manipulating several hormones or enzyme systems. Present study was conducted to determine the effect of dietary B supplementation on Ca homeostasis, bone metabolism, endocrine and antioxidant status in peripartum Murrah buffaloes.MethodsThirty advanced pregnant Murrah buffaloes (8th month pregnant) were allocated into three groups based on their most probable producing ability (MPPA) and parity (n = 10 in each group) viz. B0, B200 and B400 and supplemented with 0, 200 and 400 ppm of B in the form of boric acid. Blood samples were collected at periodic intervals (-45, -30, -21, -15, -7, 0, 7, 15, 30, 60, 90 and 120 day relative to expected date of calving) and analysed for minerals concentration, hormonal profile, bone health biomarkers and antioxidant enzymes.Results and conclusionBoron supplementation at 200 and 400 ppm increased (p < 0.05) plasma Ca, Mg and osteocalcin (OCN) concentration during postpartum stage. Higher (p < 0.05) levels of plasma 25-hydroxy vitamin D₃ were observed in both B supplemented groups as compared to B unsupplemented group irrespective of physiological stages. Plasma parathyroid hormone (PTH) and cortisol levels were lower (p < 0.05) in both B supplemented groups than B unsupplemented group, especially during postpartum stage. Whereas, plasma ferric reducing total antioxidant power (FRAP) activity was found to be higher (p < 0.05) in B supplemented groups as compared to B unsupplemented group. Furthermore, antioxidant enzymes (erythrocytic superoxide dismutase; SOD, catalase, glutathione peroxidase; GPx), plasma level of total immunoglobulins (TIg), bone specific alkaline phosphatase (BALP) and tartrate resistant acid phosphatase (TRAP) remained unaffected by dietary B supplementation. Overall, it can be concluded that supplementation of B at 200 ppm in the diet of peripartum Murrah buffaloes helped to induce metabolic adaptations for improving Ca homeostasis, bone metabolism and antioxidant status without much additional benefits at higher level used in the present study.     

The Effects of Mg Supplementation in Diets with Different Calcium Levels on the Bone Status and Bone Metabolism in Growing Female Rats

Previous studies have revealed that magnesium (Mg) plays a significant role in bone health; however, few studies have investigated the effects of Mg supplementation in diets with different calcium (Ca) levels on the bone status and bone metabolism in a growing stage. In this present study, we tested the effects of Mg supplementation on bone status in growing female rats, relative to Ca intake levels. A total of 40 Sprague–Dawley female rats aged 6 weeks were divided into the following four groups and fed for 12 weeks as indicated: (1) LCaAMg: low Ca (Ca, 0.1 % of total diet) and adequate Mg (Mg, 0.05 % of total diet), (2) LCaHMg: low Ca and high Mg ( Mg, 0.1 % of total diet), (3) ACaAMg: adequate Ca (Ca, 0.5 % of total diet) and adequate Mg, and (4) ACaHMg: adequate Ca and high Mg. Our results showed that Mg supplementation with the adequate Ca diet significantly increased the bone mineral contents, bone size (bone area and bone thickness), and bone mineral density of femur or tibia by improving bone metabolism without changing Ca absorption. Mg supplementation significantly increased the serum osteocalcin in the adequate-Ca-diet group (p?<?0.05), while the Mg supplementation significantly decreased the serum level of C-telopeptide cross-links of type I collagen in the adequate-Ca-diet group (p?<?0.001). This study suggests that Mg supplementation with adequate Ca intake in the growing stage may increase the bone mineral density and bone size by improving bone metabolism.     

Studies on the Characteristic of Element Contents in the Dominant Plant Species of the Three gorges Region in China

The characteristics of the contents of 20 elements (Al, Fe, Mn, Ca, Mg, K, S, Si, P, Cd, Cu, Zn, Ti, Ni, Sr, Mo, Na, B, Cr, V) in 16 plant species collected from the Three Gorges Region in China were investigated. The average contents of Ca, K and Mg were higher than 1 000 μg·g-1, that of Al, P, Si, Fe, S and Mn ranged between 100—1 000 μg·g-1 and Ti, Cu, Ni, Cr, Mo, Cd and V were less than 10 μg·g- 1. The level of Na content was less than that of the reported. The main character of the element contents was of the Ca> K type. The contents of P, S, Ca and K in different plant samples showed a normal distribution pattern, while Al and Mn showed a elements lognormal distribution pattern. Plant species differed greatly in the element contents. On analyzing the coefficient of variation (C. V., % ), Al, Mn, Mg, Ni, Sr and Fe had higher C.V., while the C.V. of K, S, P, Cr, Cd and Cu was less than 60%, and Cu had the lowest C.V. The correlations between Al and Fe, Al and Ti, Al and Cr, A1 and V, Cd and Sr, Cd and Mo, Fe and V, Zn and Cr, Ni and Sr, Mg and Ni, Mo and Sr, Ca and Sr, Cr and Mo, Na and Mg, Na and P, P and S were statistically significant in different plant species. The classification of the 16 plant species and 20 dements by two-way indicator species analysis (TWINSPAN) method may suggest the difference in dement contents of the different plant species.     

Ca2+ dependence of stimulated 45Ca efflux in skinned muscle fibers

Stimulation of sarcoplasmic reticulum Ca release by Mg reduction of caffeine was studied in situ, to characterize further the Ca2+ dependence observed previously with stimulation by Cl ion. 45Ca efflux and isometric force were measured simultaneously at 19 degrees C in frog skeletal muscle fibers skinned by microdissection; EGTA was added to chelate myofilament space Ca either before or after the stimulus. Both Mg2+ reduction (20 or 110 microM to 4 microM) and caffeine (5 mM) induced large force responses and 45Ca release, which were inhibited by pretreatment with 5 mM EGTA. In the case of Mg reduction, residual efflux stimulation was undetectable, and 45Ca efflux in EGTA at 4 microM Mg2+ was not significantly increased. Residual caffeine stimulation at 20 microM Mg2+ was substantial and was reduced further in increased EGTA (10 mM); at 600 microM Mg2+, residual stimulation in 5 mM EGTA was undetectable. Caffeine appears to initiate a small Ca2+-insensitive efflux that produces a large Ca2+-dependent efflux. Additional experiments suggested that caffeine also inhibited influx. The results suggest that stimulated efflux is mediated mainly or entirely by a channel controlled by an intrinsic Ca2+ receptor, which responds to local [Ca2+] in or near the channel. Receptor affinity for Ca2+ probably is influenced by Mg2+, but inhibition is weak unless local [Ca2+] is very low.     

A store-operated calcium channel in Drosophila S2 cells

Using whole-cell recording in Drosophila S2 cells, we characterized a Ca(2+)-selective current that is activated by depletion of intracellular Ca2+ stores. Passive store depletion with a Ca(2+)-free pipette solution containing 12 mM BAPTA activated an inwardly rectifying Ca2+ current with a reversal potential >60 mV. Inward currents developed with a delay and reached a maximum of 20-50 pA at -110 mV. This current doubled in amplitude upon increasing external Ca2+ from 2 to 20 mM and was not affected by substitution of choline for Na+. A pipette solution containing approximately 300 nM free Ca2+ and 10 mM EGTA prevented spontaneous activation, but Ca2+ current activated promptly upon application of ionomycin or thapsigargin, or during dialysis with IP3. Isotonic substitution of 20 mM Ca2+ by test divalent cations revealed a selectivity sequence of Ba2+ > Sr2+ > Ca2+ > Mg2+. Ba2+ and Sr2+ currents inactivated within seconds of exposure to zero-Ca2+ solution at a holding potential of 10 mV. Inactivation of Ba2+ and Sr2+ currents showed recovery during strong hyperpolarizing pulses. Noise analysis provided an estimate of unitary conductance values in 20 mM Ca2+ and Ba2+ of 36 and 420 fS, respectively. Upon removal of all external divalent ions, a transient monovalent current exhibited strong selectivity for Na+ over Cs+. The Ca2+ current was completely and reversibly blocked by Gd3+, with an IC50 value of approximately 50 nM, and was also blocked by 20 microM SKF 96365 and by 20 microM 2-APB. At concentrations between 5 and 14 microM, application of 2-APB increased the magnitude of Ca2+ currents. We conclude that S2 cells express store-operated Ca2+ channels with many of the same biophysical characteristics as CRAC channels in mammalian cells.