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To map the stability field of calcium ferrite-type Mg[Al.sub.2][O.sub.4] - [Mg.sub.2]Si[O.sub.4] solid solutions, high-pressure phase relations in the system Mg[Al.sub.2][O.sub.4] - [Mg.sub.2]Si[O.sub.4] were studied in the compositional range of 0 to 50 mol% [Mg.sub.2]Si[O.sub.4]. The calcium ferrite solid solutions are stable above 23 GPa at 1600[degrees]C, and the maximum solubility of [Mg.sub.2]Si[O.sub.4] component in Mg[Al.sub.2][O.sub.4] calcium ferrite is 34 mol%. Lattice parameters and unit-cell volume of calcium ferrite-type Mg[Al.sub.2][O.sub.4] (space group Pbnm) determined by Rietveld analysis are a = 9.9498(6) [Angstrom], b = 8.6468(6) [Angstrom], c = 2.7901(2) [Angstrom], and V = 240.02(2) [[Angstrom].sup.3]. Lattice parameters for the Mg[Al.sub.2][O.sub.4] - [Mg.sub.2]Si[O.sub.4] solid solutions with the compositions of 14, 24, and 34 mol% [Mg.sub.2]Si[O.sub.4] indicated the following compositional dependency of lattice parameters: [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] and [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] where [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] is the mole fraction of [Mg.sub.2]Si[O.sub.4] component. A linear extrapolation of the composition-molar volume relationship gave an estimated volume of 36.49(2) [cm.sup.3]/mol for the hypothetical calcium ferrite-type [Mg.sub.2]Si[O.sub.4]. This value is larger than that of the isochemical mixture of MgSi[O.sub.3] perovskite and MgO, 35.72(1) [cm.sup.3]/mol. This implies that the mixture of MgSi[O.sub.3] perovskite and MgO is more stable than the hypothetical calcium ferrite-type [Mg.sub.2]Si[O.sub.4] under the lower mantle conditions. Keywords: Mg[Al.sub.2][O.sub.4], [Mg.sub.2]Si[O.sub.4], calcium ferrite, high pressure, phase relation, Rietveld refinement

High-pressure phase stabilities of the CaSn[O.sub.3] system were investigated using density functional theory static lattice energy calculations. We have identified six phase changes in this system: perovskite-post-perovskite, post-perovskite-B2+cotunnite in CaSi[O.sub.3], B1-B2 in CaO, cassiterite-pyrite, pyrite-orthorhombic-I, and orthorhombic-I-cotunnite in Sn[O.sub.2]-. Our results demonstrate a new high-pressure phase sequence of perovskite [right arrow] post-perovskite [right arrow] B2 + cotunnite. The post-perovskite transformation occurs at ~12 GPa with ~2.5% volume reduction and then it decomposes into the oxide mixture of B2 CaO and cotunnite Sn[O.sub.2] at ~70 GPa with 8.1% volume reduction. The results also predict a few percent bulk velocity variations across these phase changes. Keywords: CaSn[O.sub.3], perovskite, post-perovskite, density functional calculation

In some cell types, oscillations in the concentration of free intracellular calcium ([[Ca.sup.2+]]) are accompanied by oscillations in the concentration of inositol 1,405-trisphosphate ([I[P.sub.3]]). However, in most cell types it is still an open question as to whether oscillations in [I[P.sub.3]] are necessary for [Ca.sup.2+] oscillations in vivo, or whether they merely follow passively. Using a wide range of models, we show that the response to an artificially applied pulse of I[P.sub.3] can be used to distinguish between these two cases. Hence, we show that muscarinic receptor-mediated, long-period [Ca.sup.2+] oscillations in pancreatic acinar cells depend on [I[P.sub.3]] oscillations, whereas shortperiod [Ca.sup.2+] oscillations in airway smooth muscle do not. mathematical model

Corn tortillas are the staple food of Mexico. During their preparation, calcium is added to the tortillas; therefore, tortillas are the main source of calcium for a large proportion of the population. The bioavailability of calcium from lime-treated tortillas in humans is not known. The objectives of the present study were to determine calcium absorption from corn tortilla, to determine the effect of lime treatment on calcium absorption from corn tortilla, and to compare calcium absorption from tortilla prepared with a commercial corn flour and tortillas prepared with the traditional lime treatment at home. Nonpregnant, nonlactating women (n = 9) were administered 3 different treatments: 1) 180 g of corn tortilla prepared from corn flour with no lime treatment (CF), 2) 180 g of corn tortilla prepared from lime-treated commercial corn flour (LTCCF), or 3) 180 g of corn tortillas prepared from lime-treated home-prepared corn flour (LTHCF). Calcium absorption was measured using an established dual-tracer stable isotope technique. Calcium absorption of CF, LTCCF, and LTHCF was (mean [+ or -] SD): 44 [+ or -] 3.2, 32 [+ or -] 4.4, and 30 [+ or -] 2.4%, respectively; the fractional calcium absorption from CF differed from that of either LTCCF or LTHCF (P < 0.01). The total amount of calcium absorbed per treatment was higher in LTHCF (98.10 mg [+ or -] 21.7) than in LTCCF (59.9 mg [+ or -] 23.7, P < 0.001) and CF (3.78 mg [+ or -] 0.9, P < 0.0.001). In conclusion, calcium absorption from corn tortillas is high and dependent on calcium concentration. The addition of calcium during lime treatment increases calcium concentration and total calcium absorption. KEY WORDS: * calcium absorption * tortillas * lime treatment * stable isotopes

The contributions of Ca(super 2+) and Ca(super 2+) binding proteins to health and disease were addressed in a meeting held in April 2005 in Bnaff, Canada. Insights got from the mechanical studies offered the potential for new therapeutic approaches to combat a variety of diseases resulting from alterations in Ca(super 2+) homeostasis.

Light stimuli produce graded hyperpolarizations of the photoreceptor plasma membrane and an associated decrease in a voltage-gated calcium channel conductance that mediates release of glutamate neurotransmitter. The [Ca.sub.v]1.4 channel is thought to be involved in this process. The CACNA1F gene encodes the pore-forming subunit of the [Ca.sub.v]1.4 channel and various mutations in CACNA1F cause X-linked incomplete congenital stationary night blindness (CSNB2). The molecular mechanism of the pathology underlying the CSNB2 phenotype remains to be established. Recent clinical investigations of a New Zealand family found a severe visual disorder that has some clinical similarities to, but is clearly distinct from, CSNB2. Here, we report investigations into the molecular mechanism of the pathology of this condition. Molecular genetic analyses identified a previously undescribed nucleotide substitution in CACNA1F that is predicted to encode an isoleucine to threonine substitution at CACNA1F residue 745. The I745T CACNA1F allele produced a remarkable approximately -30-mV shift in the voltage dependence of [Ca.sub.v]1.4 channel activation and significantly slower inactivation kinetics in an expression system. These findings imply that substitution of this wild-type residue in transmembrane segment IIS6 may have decreased the energy required to open the channel. Collectively, these findings suggest that a gain-of-function mechanism involving increased [Ca.sub.v]1.4 channel activity is likely to cause the unusual phenotype.

Identification of the mechanisms involved in the pathology of nutrient deficiency provides an understanding of nutrient functions, their role in metabolism, and interactions between nutrients. However, evidence has emerged in recent years that low (suboptimal) intakes of micronutrients are associated with an elevated risk of chronic diseases. The description of micronutrient associations with chronic disease as a deficiency disease does not capture the complexity of these relations. It implies a significant oversimplification of this relation and detracts from the need for development of new approaches to this area of study. Epidemiologic study designs are essential for progress in understanding the micronutrient--chronic-disease relations, and these are described. Two areas wherein epidemiological tools could be incorporated into experimental designs have been vitamin D and prostate cancer, and vitamin D and colon cancer. In each case, biomarkers of exposure, intermediary markers, and mechanisms have been identified and could be implemented in new experimental designs. Measures of exposure would be improved by incorporation of measurements of vitamin D status such as serum 25-hydroxyvitamin D measurements. Several intermediary markers are discussed and may be useful in the characterization of responses. Such developments should aid in the interpretation of studies and identify vitamin D, as well as calcium intakes, that will aid in the prevention of prostate and colon cancer. KEY WORDS: * vitamin D * prostate cancer * colon cancer * biomarkers * epidemiology

The major plasma membrane Ca(super 2)+ extruding system, the Na+/Ca(super 2)+ exchanger (NCX) that is cleared during brain ischemia and in neurons undergoing excitotoxicity is described. Proteolytic inactivation of NCX-driven neuronal Ca(super 2)+ extrusion is responsible for the delayed excitotoxic Ca(super 2)+ deregulation and neuronal death.

The very different courtship flashes of Photuris versicolor and Photuris lucicrescens males mirror the pattern of neural impulses produced by their brain. Their lanterns luminescence very differently, however, in response to direct, electrical stimulation. Whereas P. lucicrescens lanterns glow in response to high frequency, continuous electrical stimulation, those of P. versicolor produce only rapid, triple-pulsed flashlettes that resemble, but are not identical to, their courtship flashes. In addition, the exposed lantern tissue of P. versicolor males, when immersed in firefly saline high in potassium and calcium ions, scintillates with hundreds of photocytes flashing in random fashion. P. lucicrescens male lanterns, so treated, only glow. Tests of P. versicolor lanterns with salines of different composition suggest that calcium ions are essential in producing this intense, long lasting scintillation response and are therefore possibly implicated in the final stages of flash control in this species.

The high-resolution laser-induced fluorescence spectrum of a molecular beam sample of calcium monohydride (CaH) in the region of the strongly overlapped (1,0) [A.sup.2][PHI] - [X.sup.2][[SIGMA].sup.+] and (0,0) [B.sup.2][[SIGMA].sup.+] - [X.sup.2][[SIGMA].sup.+] band systems near 63 nm and the (0,0) [A.sup.2][PHI] - [X.sup.2][[SIGMA].sup.+] band system near 690 nm have been recorded and analyzed. The spectral features exhibit a small splitting that is attributed to proton magnetic hyperfine interaction in the [X.sup.2][[SIGMA].sup.+] (v = 0) state. The energy levels of the [A.sup.2][PHI](v = 0) vibronic state were modeled using a traditional "effective" Hamiltonian approach, whereas those for the interacting [A.sup.2][PHI](v = 1)/[B.sup.2][[SIGMA].sup.+] (v = 0) vibronic levels were modeled by augmenting the traditional effective Hamiltonian with terms to account for local perturbations. An interpretation of the field-free parameters is presented. Key words: calcium monohydride, molecular beam, fluorescence.

The performance of a selection of theoretical procedures in describing the binding of Ca(super 2+) to ammonia and formaldehyde was assessed. Ca(super 2+) was predicted to bind more strongly to formaldehyde than to ammonia, in contrast to the ordering of proton and Li(super +1) affinities for the two molecules.

Interaction between the surface of the calcium pyrophosphate dihydrate (CPPD) crystals and the extracellular layer of the hydrated dimyristoyl phosphatidylcholin (DMPC) phospholipid bilayer is studied by using molecular dynamics (MD).

Small-angle X-ray scattering (SAXS) is used to study the structure of a complex formed from DNA, calcium and DPPC. The effects of calcium on lipids are studied.

Ryanodine receptors (RyRs) are Ca(super ++) channels that control cellular functions. An estimation of the RyR2 ion diffusion constants and electrostatic interactions, in a self-consistent coherent formulation, is provided by the extended PNP.

A study of the uderpotential depostion (UPD) of Te monolayers onto Au electrodes from perchloric acid solution using electrochemical quartz microgravimetry (EQCM) and chronocoulometry is reported. Analysis of the current time data indicates that this process occurs by a two-dimensional instantaneous nucleation and growth mechanism, resulting in an ordered overlayer with a fractional coverage of ca. 0.41.

The refractive indices of synthetic calcium fluoride for 69 wavelengths from 138 nm in the deep ultraviolet to 2326 nm in the near infrared were measured by the minimum-deviation method in a nitrogen environment. We made these measurements at 20[degrees] and 25[degrees]C, respectively, to determine the thermal coefficients of the refractive index over this wide-wavelength region. These refractive indices were fitted to a four-term Sellmeier dispersion formula. The temperature coefficients of the refractive index were fitted to a Hoffman-type dispersion formula. The standard deviation of the residual between the observed values and the calculated values was 0.6 [10.sup.-6] for the refractive index and was 0.13 [10.sup.-6]/[degrees] C for the temperature coefficient of the refractive index.

We have studied short-range cation ordering across the diopside (CaMg[Si.sub.2][O.sub.6]-Ca-Tschermak pyroxene (Ca[Al.sub.2]Si[O.sub.6]) (Di-CaTs) solid solution in samples synthesized at 1400 [degrees] C and 2 GPa, for 24 hours. Peak positions in [sup.29]Si MAS NMR spectra are sensitive to Al substitution, both in the corner-sharing NN tetrahedral sites on the single chain and in one of the three NN octahedral M1 sites. The substitution of A1 for Mg on MI causes the [sup.29]Si chemical shift to be shielded by about the same magnitude as the deshielding caused by substitution of Al for Si in NN tetrahedra, causing severe peak overlap among central peaks. Two pairs of the unique local environments have very similar chemical shifts, leaving only four peaks resolved in the spectrum, for which six site assignments have been made. [sup.29]Si MAS NMR peak intensities for end-member CaTs are consistent with 70% of the Si in the tetrahedral chain being locally ordered into alternating [sup.[4]]AI-O-Si-O-[sup.[4]]Al linkages, although space group C2/c would suggest that Si and Al are long-range disordered over the tetrahedral chain. CaTs clearly violates Lowenstein's (1954) Al-O-Al avoidance principle, with 0.175 Al-O-Al linkages per formula unit (based on six O atoms per formula unit), as calculated from observed [sup.29]Si MAS NMR peak intensities. For intermediate members of the solid solution, site populations have been modeled using a random distribution model (RD), an Al-O-Al avoidance model (AA) and a modified AA model which couples the cation distribution between the tetrahedral and octahedral sites (AAOC). The RD model fits the [sup.29]Si MAS NMR peak intensities poorly. The AA and AAOC models fit the [sup.29]Si NMR data well to at least 75% CaTs, suggesting that diopside-rich Di-CaTs clinopyroxenes obey Lowenstein's Al-O-Al avoidance principle. For compositions >75% CaTs, observed cation distributions deviate considerably from that predicted by Al-O-Al avoidance, indicating formation of Al-O-Al linkages. The AAOC model yields an improved fit to the observed [sup.29]Si MAS NMR intensities, particularly near [Di.sub.50]Ca[Ts.sub.50], implying the presence of [sup.[4]]Si-O-[sup.[6]]Mg and [sup.[4]]AI-O-[sup.[6]]A1 couples. This suggests the presence of short-range ordering on both tetrahedral and octahedral sites in Di-CaTs pyroxenes. The high sensitivity to octahedral Al substitution observed in these chain silicates is not observed by [sup.29]Si MAS NMR of more-polymerized silicates, such as framework and sheet structures. Thus, [sup.[29]]Si MAS NMR of pyroxenes has potential to reveal tetrahedral-octahedral cation coupling and octahedral cation ordering information, which is potentially important for geothermobarometry of aluminous pyroxenes.

Three types of calcium carbonyl complexes are formed due to adsorption of CO on CaNaY at 85K. These three principle bands are formed in the carbonyl stretching region at 2185, 2167 and 2145 cm-1.

A study was conducted on two different soluble polymers where it is suggested that noncovalent interaction and cooperation between soluble macromolecules play key roles in controlling the growth of biominerals. The results suggest a novel and facile route toward biomimetic inorganic synthesis.

The equilibrium structure and potential-energy surface of calcium difluoride, CaF(sub 2) is determined from large-scale ab initio calculations using the coupled-cluster method, CCSD(T), in conjunction with basis sets of quadruple and quintuple zeta quality. The high-quality ab initio approach is applied to characterize the 3D potential-energy surface and vibrational-rotational energy levels of calcium difluoride.

Ca(super 2+) toxicity remains the central focus of ischemic brain injury, and acidosis is a common feature of ischemia. The study shows that acidosis activates Ca(super 2+)-permeable acid-sensing ion channels (ASICs).

A detailed investigation of the solvation structure of dilute Ca(super 2+) -and Sr(super 2+) -water solution and also Ca(super 2+) -methanol solution using a classical MD techniques and polarization potential models, is presented. The molecular dynamics (MD) results were coupled to electron scattering simulations in order to generate the Ca(super 2+) and Sr(super 2+) extended X-ray absorption fine structure (EXAFS) spectra.

(super 17)O magic angle spinning (MAS) and triple quantum magic angle spinning (3QMAS) NMR is used to show nonrandom distributions of the network-modifying cations Na and Ca in Ca-Na silicate glasses, by probing the atomic configuration around the nonbridging oxygens. Nonrandomness in Na-Ca mixing was observed in (super 17)O MAS and 3QMAS NMR where several nonbridging oxygen peaks such as Na-O-(super [4])Si, and mixed peaks are partially resolved.

Ultrasonic absorption spectra between 800kHz and 2GHz and sound velocities of aqueous solutions of calcium nitrate are measured at different salt concentrations and temperatures. The high-frequency ultrasonic relaxation is assumed to be due to the equilibrium between an outersphere ion complex and a contact ion pair.

Research is done on the reactivity of gas-phase ground-state calcium atoms with O2, which is reported from 296 to 623 K. In conclusion the RRKM theory, fitted to the experimental data, predicts the following expression for the rate coefficient from 140 to 1000 K and 10(super -5) to 10(super 3) Torr: log(k(sub rec, 0)/cm(super 6) molecule(super -2) s(super -1)) = -57.10 + 19.70 log T -- 3.410(log T)(super 2), k(sub rec, infinity) = 1.36 x 10(super -10) exp(-- 1020/T) cm(super 3) molecule(super -1) s(super -1), and Fc = 0.67.

The absorbance and the steady-state and time-resolved fluorescence responses to Ca(sub 2+) induced conformational changes within cod 111parvalbumin (C3P), which was labeled at cystein-18 with the fluorescent probes fluorescein, acrylodan or nitrobenzoxadiazole (NBD) is examined. The two probes produced poor responses indicating the difficulty associated with predicting the behavior of a labeled protein.

Monte Carlo simulation is used as a means to select calcium over sodium in a biological channel. The selectivity results from interplay between the volume exclusion effect due to the narrow channel diameter and the negative charge on the glutamates.

Enrichments in boron-10/boron-11 in a calcium-aluminum-rich inclusion from the Allende carbonaceous chondrite are correlated with beryllium/boron in a manner indicative of the in situ decay of short-lived beryllium-10. Because this radionuclide is produced only by nuclear spallation reactions, its existence in early solar system materials attests to intense irradiation processes in the solar nebula. The particle fluence inferred from the initial beryllium-10/beryllium-9 is sufficient to produce other short-lived nuclides, calcium-41 and manganese-53, found in meteorites, but the high canonical abundance of aluminum-26 may still require seeding of the solar system by radioactive stellar debris., When the oldest solar system materials, the Ca-Al-rich inclusions (CAIs) of primitive chondrite meteorites (1), first crystallized in the solar nebula, their major elements included small concentrations of short-lived radioactive [...]

Changes in intracellular calcium concentration ([[[Ca.sup.2+]].sub.i]) that occur after [Ca.sup.2+] influx through N-methyl-D-aspartate--type glutamate receptors (NMDARs) play a key role in long-term plastic changes in postsynaptic function that are thought [...]

In a controlled-diet study of 15 healthy postmenopausal women, ARS scientists found that a high-meat diet--even with low but average calcium intake--didn't inhibit women's retention of calcium. In the crossover [...]

The albumen gland of the freshwater pulmonate snail Helisoma duryi produces and secretes the perivitelline fluid, which coats fertilized eggs and provides nutrients to the developing embryos. It is known that the perivitelline fluid secretion is stimulated by dopamine and forskolin and that Gi and Gs proteins, adenylate cyclase and protein kinase A are involved. This paper provides evidence of the role of calcium, phospholipase C, I[P.sub.3] and protein kinase C in perivitelline fluid secretion by the albumen gland based on protein secretion experiments and I[P.sub.3] assays. Both extracellular and intracellular calcium plays a role in the signaling process of protein secretion by the albumen gland. Cyclic AMP, synthesized by receptor coupled adenylate cyclase, activates protein kinase A, which presumably phosphorylates L-type calcium channels on the plasma membrane leading to an increase in cytosolic calcium concentration, which is a prerequisite for the stimulation of perivitelline fluid exocytosis. Phospholipase C appears not to be involved in regulating protein secretion and, consequently, I[P.sub.3], diacylglycerol and protein kinase C are not involved either. Intracellular calcium stores seem to play a role in the signaling, possibly through other types of calcium channels and other signaling pathways since neither I[P.sub.3] receptors nor ryanodine receptors were implicated. Combining the data in this paper with the results from our earlier studies, a model for signaling of perivitelline fluid release from the albumen gland secretory cells is proposed.