Seawater calcium isotope ratios across the Eocene-Oligocene Transition from Pacific Ocean - Marine Barite

During the Eocene-Oligocene transition (EOT, ca. 34 Ma), Earth's climate cooled significantly from a greenhouse to an icehouse climate, while the calcite (CaCO3) compensation depth (CCD) in the Pacific Ocean increased rapidly. Fluctuations in the CCD could result from various processes that create an imbalance between calcium (Ca) sources to, and sinks from, the ocean (e.g., weathering and CaCO3 deposition), with different effects on the isotopic composition of dissolved Ca in the oceans due to differences in the Ca isotopic composition of various inputs and outputs. We used Ca isotope ratios (d44/40Ca) of coeval pelagic marine barite and bulk carbonate to evaluate changes in the marine Ca cycle across the EOT. We show that the permanent deepening of the CCD was not accompanied by a pronounced change in seawater d44/40Ca, whereas time intervals in the Neogene with smaller carbonate depositional changes are characterized by seawater d44/40Ca shifts. This suggests that the response of seawater d44/40Ca to changes in weathering fluxes and to imbalances in the oceanic alkalinity budget depends on the chemical composition of seawater. A minor and transient fluctuation in the Ca isotope ratio of bulk carbonate may reflect a change in isotopic fractionation associated with CaCO3 precipitation from seawater due to a combination of factors, including changes in temperature and/or in the assemblages of calcifying organisms.

Exploring the parameter space of a rabbit ventricular action potential model to investigate the effect of variation on action potential and calcium transients

Computational models for cardiomyocyte action potentials (AP) often make use of a large parameter set. This parameter set can contain some elements that are fitted to experimental data independently of any other element, some elements that are derived concurrently with other elements to match experimental data, and some elements that are derived purely from phenomenological fitting to produce the desired AP output. Furthermore, models can make use of several different data sets, not always derived for the same conditions or even the same species. It is consequently uncertain whether the parameter set for a given model is physiologically accurate. Furthermore, it is only recently that the possibility of degeneracy in parameter values in producing a given simulation output has started to be addressed. In this study, we examine the effects of varying two parameters (the L-type calcium current (I(CaL)) and the delayed rectifier potassium current (I(Ks))) in a computational model of a rabbit ventricular cardiomyocyte AP on both the membrane potential (V(m)) and calcium (Ca(2+)) transient. It will subsequently be determined if there is degeneracy in this model to these parameter values, which will have important implications on the stability of these models to cell-to-cell parameter variation, and also whether the current methodology for generating parameter values is flawed. The accuracy of AP duration (APD) as an indicator of AP shape will also be assessed.

Effects of varied ionic calcium and phosphate on the proliferation, osteogenic differentiation and mineralization of human periodontal ligament cells in vitro

Background and Objective: A number of bone filling materials containing calcium (Ca++) and phosphate (P) ions have been used in the repair of periodontal bone defects; however, the effect that local release of Ca++ and P ions have on biological reactions is not fully understood. In this study, we investigated the effects of various levels of Ca++ and P ions on the proliferation, osteogenic differentiation, and mineralization of human periodontal ligament cells (hPDLCs). Materials and Methods: hPDLCs were obtained using an explant culture method. Defined concentrations and ratios of ionic Ca++ to inorganic P were added to standard culture and osteogenic induction media. The ability of hPDLCs to proliferate in these growth media was assayed using the Cell Counting Kit-8 (CCK-8). Cell apoptosis was evaluated by FITC-Annexin V/PI double staining method. Osteogenic differentiation and mineralization were investigated by morphological observations, alkaline phosphatase (ALP) activity, and Alizarin red S/von Kossa staining. The mRNA expression of osteogenic related markers was analyzed using a reverse transcriptase polymerase chain reaction (RT-PCR). Results: Within the ranges of Ca++ and P ions concentrations tested, we observed that increased concentrations of Ca++ and P ions enhanced cell proliferation and formation of mineralized matrix nodules; whereas ALP activity was reduced. The RT-PCR results showed that elevated concentrations of Ca++ and P ions led to a general increase of Runx2 mRNA expression and decreased ALP mRNA expression, but gave no clear trend on OCN mRNA levels. Conclusion: The concentrations and ratios of Ca++ and P ions could significantly influence proliferation, differentiation, and mineralization of hPDLCs. Within the range of concentrations tested, we found that the combination of 9.0 mM Ca++ ions and 4.5 mM P ions were the optimum concentrations for proliferation, differentiation, and mineralization in hPDLCs.

Calcium ions promote osteogenic differentiation and mineralization of human dental pulp cells : implication for pulp capping materials

Calcium (Ca) is the main element of most pulp capping materials and plays an essential role in mineralization. Different pulp capping materials can release various concentrations of Ca ions leading to different clinical outcomes. The purpose of this study was to investigate the effects of various concentrations of Ca ions on the growth and osteogenic differentiation of human dental pulp cells (hDPCs). Different concentrations of Ca ions were added to growth culture medium and osteogenic inductive culture medium. A Cell Counting Kit-8 (CCK-8) was used to determine the proliferation of hDPCs in growth culture medium. Osteogenic differentiation and mineralization were measured by alkaline phosphatase (ALP) assay, Alizarin red S/von kossa staining, calcium content quantitative assay. The selected osteogenic differentiation markers were investigated by quantitative real-time polymerase chain reaction (qRT-PCR). Within the range of 1.8–16.2 mM, increased concentrations of Ca ions had no effect on cell proliferation, but led to changes in osteogenic differentiation. It was noted that enhanced mineralized matrix nodule formation was found in higher Ca ions concentrations; however, ALP activity and gene expression were reduced. qRT-PCR results showed a trend towards down-regulated mRNA expression of type I collagen (COL1A2) and Runx2 at elevated concentrations of Ca ions, whereas osteopontin (OPN) and osteocalcin (OCN) mRNA expression was significantly up-regulated. Ca ions content in the culture media can significantly influence the osteogenic properties of hDPCs, indicating the importance of optimizing Ca ions release from dental pulp capping materials in order to achieve desirable clinical outcomes.

Induction of epithelial-mesenchymal transition (EMT) in breast cancer cells is calcium signal dependent

Signals from the tumor microenvironment trigger cancer cells to adopt an invasive phenotype through epithelial-mesenchymal transition (EMT). Relatively little is known regarding key signal transduction pathways that serve as cytosolic bridges between cell surface receptors and nuclear transcription factors to induce EMT. A better understanding of these early EMT events may identify potential targets for the control of metastasis. One rapid intracellular signaling pathway that has not yet been explored during EMT induction is calcium. Here we show that stimuli used to induce EMT produce a transient increase in cytosolic calcium levels in human breast cancer cells. Attenuation of the calcium signal by intracellular calcium chelation significantly reduced epidermal growth factor (EGF)- and hypoxia-induced EMT. Intracellular calcium chelation also inhibited EGF-induced activation of signal transducer and activator of transcription 3 (STAT3), while preserving other signal transduction pathways such as Akt and extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation. To identify calcium-permeable channels that may regulate EMT induction in breast cancer cells, we performed a targeted siRNA-based screen. We found that transient receptor potential-melastatin-like 7 (TRPM7) channel expression regulated EGF-induced STAT3 phosphorylation and expression of the EMT marker vimentin. Although intracellular calcium chelation almost completely blocked the induction of many EMT markers, including vimentin, Twist and N-cadherin, the effect of TRPM7 silencing was specific for vimentin protein expression and STAT3 phosphorylation. These results indicate that TRPM7 is a partial regulator of EMT in breast cancer cells, and that other calcium-permeable ion channels are also involved in calcium-dependent EMT induction. In summary, this work establishes an important role for the intracellular calcium signal in the induction of EMT in human breast cancer cells. Manipulation of calcium-signaling pathways controlling EMT induction in cancer cells may therefore be an important therapeutic strategy for preventing metastases.

Effects of dietary phosphorus and calcium-to-phosphorus ratio on calcium and bone metabolism in healthy 20- to 43-year-old Finnish women

Dietary habits have changed during the past decades towards an increasing consumption of processed foods, which has notably increased not only total dietary phosphorus (P) intake, but also intake of P from phosphate additives. While the intake of calcium (Ca) in many Western countries remains below recommended levels (800 mg/d), the usual daily P intake in a typical Western diet exceeds by 2- to 3-fold the dietary guidelines (600 mg/d). The effects of high P intake in healthy humans have been investigated seldom. In this thesis healthy 20- to 43-year-old women were studied. In the first controlled study (n = 14), we examined the effects of P doses, and in a cross-sectional study (n = 147) the associations of habitual P intakes with Ca and bone metabolism. In this same cross-sectional study, we also investigated whether differences exist between dietary P originating from natural P sources and phosphate additives. The second controlled study (n = 12) investigated whether by increasing the Ca intake, the effects of a high P intake could be reduced. The associations of habitual dietary calcium-to-phosphorus ratios (Ca:P ratio) with Ca and bone metabolism were determined in a cross-sectional study design (n = 147). In the controlled study, the oral intake of P doses (495, 745, 1245 and 1995 mg/d) with a low Ca intake (250 mg/d) increased serum parathyroid hormone (S-PTH) concentration in a dose-dependent manner. In addition, the highest P dose decreased serum ionized calcium (S-iCa) concentration and bone formation and increased bone resorption. In the second controlled study with a dietary P intake of 1850 mg/d, by increasing the Ca intake from 480 mg/d to 1080 mg/d and then to 1680 mg/d, the S-PTH concentration decreased, the S-iCa concentration increased and bone resorption decreased dose-dependently. However, not even the highest Ca intake could counteract the effect of high dietary P on bone formation, as indicated by unchanged bone formation activity. In the cross-sectional studies, a higher habitual dietary P intake (>1650 mg/d) was associated with lower S-iCa and higher S-PTH concentrations. The consumption of phosphate additive-containing foods was associated with a higher S-PTH concentration. Moreover, habitual low dietary Ca:P ratios (≤0.50, molar ratio) were associated with higher S-PTH concentrations and 24-h urinary Ca excretions, suggesting that low dietary Ca:P ratios may interfere with homeostasis of Ca metabolism and increase bone resorption. In summary, excessive dietary P intake in healthy Finnish women seems to be detrimental to Ca and bone metabolism, especially when dietary Ca intake is low. The results indicate that by increasing dietary Ca intake to the recommended level, the negative effects of high P intake could be diminished, but not totally prevented. These findings imply that phosphate additives may be more harmful than natural P. Thus, reduction of an excessively high dietary P intake is also beneficial for healthy individuals.

Atypical correlation of otolith strontium : calcium and barium : calcium across a marine–freshwater life history transition of a diadromous fish

Variation in strontium (Sr) and barium (Ba) within otoliths is invaluable to studies of fish diadromy. Typically, otolith Sr : Ca is positively related to salinity, and the ratios of Ba and Sr to calcium (Ca) vary in opposite directions in relation to salinity. In this study of jungle perch, Kuhlia rupestris, otolith Sr : Ca and Ba : Ca, however, showed the same rapid increase as late-larval stages transitioned directly from a marine to freshwater environment. This transition was indicated by a microstructural check mark on otoliths at 35–45 days age. As expected ambient Sr was lower in the fresh than the marine water, however, low Ca levels (0.4 mg L–1) of the freshwater resulted in the Sr : Ca being substantially higher than the marine water. Importantly, the otolith Sr : Ba ratio showed the expected pattern of a decrease from the marine to freshwater stage, illustrating that Sr : Ba provided a more reliable inference of diadromous behaviour based on prior expectations of their relationship to salinity, than did Sr : Ca. The results demonstrate that Ca variation in freshwaters can potentially be an important influence on otolith element : Ca ratios and that inferences of marine–freshwater habitat use from otolith Sr : Ca alone can be problematic without an understanding of water chemistry.

Influence of anthropogenic contamination on groundwater chemistry in Mulbagal town, Kolar District, India

Geochemical studies are performed to examine the impact of leachate infiltration from on-site sewage disposal systems on the groundwater chemistry in Mulbagal town, Kolar District, Karnataka State, India. The leachate infiltration imposed nitrate concentrations ranging from 4 mg/L to 388 mg/L in the groundwater samples; it was observed that 79% of the samples exhibited nitrate concentrations in excess of drinking water permissible limit (45 mg/L). The average (of 43 measurements) E. coli levels in the groundwater samples corresponded to 189 MPN/100 mL and 55% of the samples tested exhibit pathogen contamination. Results also showed that the groundwater in the study area is characterized by acidic pH, large calcium + magnesium ion and Na/Cl ratios of < unity causing majority of the ground water samples to classify as Ca-Mg-Cl type and Na-Cl type. Saturation index (SI) computation using Visual MINTEQ program showed that the groundwater samples are under-saturated with respect to calcite. The theoretical SI values (of calcite) however suggested that the groundwater samples ought to be over-saturated with calcite. Under-saturation of the groundwater samples with calcite is attributed to increased dissolution of the mineral in the acidic environment of the groundwater.

Enrichment of rotifer Brachionus rotundiformis with calcium

Possibility of enrichment of rotifer (Brachionus rotondiformis) with calcium (Ca) for feeding the fish fry was investigated. Rotifer was kept for 24 h with aeration in normal seawater (Treatment 1), seawater with 400 mg/l supplemental Ca from Ca-lactate (Treatment 2) and seawater with 400 mg/l supplemental Ca from Ca-chloride (Treatment 3). After the experimental period, Ca contents of rotifer were 0.20, 0.29 and 0.39% of dry weight in T-1, T-2 and T-3, respectively. Ca content of media did not affect phosphorus, zinc and manganese contents of rotifer. Results revealed that rotifer can be enriched with Ca for feeding fish fry and Ca-chloride might be a better source for Ca enrichment.

Necessity of dietary calcium supplement in file fish (Monacanthus cirrhifer)

File fish, Monacanthus cirrhifer, juveniles with initial mean body weight of 0.27g were fed purified diets with or without calcium (Ca) supplement for 10 weeks at a water temperature of 27.0±1.4°C. Growth was significantly low in fish fed diet without Ca supplement than fish fed diet with Ca supplement. Feed efficiency and condition of fish were also significantly decreased in absence of a dietary Ca supplementation, Minerals contents of bone were similar in both the treatment groups and did not appear as a suitable indicator of Ca requirement. It appeared that Ca supplement to the purified diet is necessary for file fish for their proper growth and feed utilization.

CalDAG-GEFI is at the nexus of calcium-dependent platelet activation.

The importance of the second messengers calcium (Ca(2+)) and diacylglycerol (DAG) in platelet signal transduction was established more than 30 years ago. Whereas protein kinase C (PKC) family members were discovered as the targets of DAG, little is known about the molecular identity of the main Ca(2+) sensor(s). We here identify Ca(2+) and DAG-regulated guanine nucleotide exchange factor I (CalDAG-GEFI) as a critical molecule in Ca(2+)-dependent platelet activation. CalDAG-GEFI, through activation of the small GTPase Rap1, directly triggers integrin activation and extracellular signal-regulated kinase-dependent thromboxane A(2) (TxA(2)) release. CalDAG-GEFI-dependent TxA(2) generation provides crucial feedback for PKC activation and granule release, particularly at threshold agonist concentrations. PKC/P2Y12 signaling in turn mediates a second wave of Rap1 activation, necessary for sustained platelet activation and thrombus stabilization. Our results lead to a revised model for platelet activation that establishes one molecule, CalDAG-GEFI, at the nexus of Ca(2+)-induced integrin activation, TxA(2) generation, and granule release. The preferential activation of CalDAG-GEFI over PKC downstream of phospholipase C activation, and the different kinetics of CalDAG-GEFI- and PKC/P2Y12-mediated Rap1 activation demonstrate an unexpected complexity to the platelet activation process, and they challenge the current model that DAG/PKC-dependent signaling events are crucial for the initiation of platelet adhesion.

Shoot calcium and magnesium concentrations differ between subtaxa, are highly heritable, and associate with potentially pleiotropic loci in Brassica oleracea

Calcium (Ca) and magnesium (Mg) are the most abundant group II elements in both plants and animals. Genetic variation in shoot Ca and shoot Mg concentration (shoot Ca and Mg) in plants can be exploited to biofortify food crops and thereby increase dietary Ca and Mg intake for humans and livestock. We present a comprehensive analysis of within-species genetic variation for shoot Ca and Mg, demonstrating that shoot mineral concentration differs significantly between subtaxa (varietas). We established a structured diversity foundation set of 376 accessions to capture a high proportion of species-wide allelic diversity within domesticated Brassica oleracea, including representation of wild relatives (C genome, 1n = 9) from natural populations. These accessions and 74 modern F-1 hybrid cultivars were grown in glasshouse and field environments. Shoot Ca and Mg varied 2- and 2.3-fold, respectively, and was typically not inversely correlated with shoot biomass, within most subtaxa. The closely related capitata (cabbage) and sabauda (Savoy cabbage) subtaxa consistently had the highest mean shoot Ca and Mg. Shoot Ca and Mg in glasshouse-grown plants was highly correlated with data from the field. To understand and dissect the genetic basis of variation in shoot Ca and Mg, we studied homozygous lines from a segregating B. oleracea mapping population. Shoot Ca and Mg was highly heritable (up to 40). Quantitative trait loci (QTL) for shoot Ca and Mg were detected on chromosomes C2, C6, C7, C8, and, in particular, C9, where QTL accounted for 14 to 55 of the total genetic variance. The presence of QTL on C9 was substantiated by scoring recurrent backcross substitution lines, derived from the same parents. This also greatly increased the map resolution, with strong evidence that a 4-cM region on C9 influences shoot Ca. This region corresponds to a 0.41-Mb region on Arabidopsis (Arabidopsis thaliana) chromosome 5 that includes 106 genes. There is also evidence that pleiotropic loci on C8 and C9 affect shoot Ca and Mg. Map-based cloning of these loci will reveal how shoot-level phenotypes relate to Ca 21 and Mg 21 uptake and homeostasis at the molecular level.

Regulation of Multidrug Resistance-Associated Protein 2 by Calcium Signaling in Mouse Liver

Mu hiding resistance associated protein 2 (Mrp2) is a canalicular transporter responsible for organic anion secretion into bile. Mrp2 activity is regulated by insertion into the plasma membrane; however, the factors that control this are not understood. Calcium (Ca(2+)) signaling regulates exocytosis of vesicles in most cell types, and the type II inositol 1,4,5-triphosphate receptor (InsP(3)R2) regulates Ca(2+) release in the canalicular region of hepatocytes. However, the role of InsP(3)R2 and of Ca(2+) signals in canalicular insertion and function of Mrp2 is not known. The aim of this study was to determine the role of InsP(3)R2-mediated Ca(2+) signals in targeting Mrp2 to the canalicular membrane. Livers, isolated hepatocytes, and hepatocytes in collagen sandwich culture from wild-type (WT) and InsP(3)R2 knockout (KO) mice were used for western blots, confocal immunofluorescence, and time-lapse imaging of Ca(2+) signals and of secretion of a fluorescent organic anion. Plasma membrane insertion of green fluorescent protein (GFP)-Mrp2 expressed in HepG2 cells was monitored by total internal reflection microscopy. InsP(3)R2 was concentrated in the canalicular region of WT mice but absent in InsP(3)R2 KO livers, whereas expression and localization of InsP(3)R1 was preserved, and InsP(3)R3 was absent from both WT and KO livers. Ca(2+) signals induced by either adenosine triphosphate (ATP) or vasopressin were impaired in hepatocytes lacking InsP(3)R2. Canalicular secretion of the organic anion 5-chloromethylfluorescein diacetate (CMFDA) was reduced in KO hepatocytes, as well as in WT hepatocytes treated with 1,2-bis(o-aminophenoxy)ethane-N,N,N`,N`-tetra-acetic acid (BAPTA). Moreover, the choleretic effect of tauroursodeoxycholic acid (TUDCA) was impaired in InsP(3)R2 KO mice. Finally, ATP increased GFP-Mrp2 fluorescence in the plasma membrane of HepG2 cells, and this also was reduced by BAPTA. Conclusion: InsP(3)R2-mediated Ca(2+) signals enhance organic anion secretion into bile by targeting Mrp2 to the canalicular membrane. (HEPATOLOGY 2010;52:327-337)

ATP pulse and calcium homeostasis in cells from hepatopancreas of Dilocarcinus pagei, a freshwater crab

Calcium (Ca) is critical for crustaceans due to their molting cycle and its presence in the carapace as calcium carbonate, apart from the usual functions of Ca, such as cell signalling. Ca transport in Dilocarcinus pagei, a freshwater crab, was studied in isolated cells from hepatopancreas to further characterize Ca transport mechanisms in these crabs. Cells were isolated and loaded with Fluo-3, a calcium fluorescent dye. Three different cell treatments were performed: Group 1 cells were Ca free during cell dissociation, and calcium was present (at 1mM) for fluorescence cell loading and transport experiments (FC); Group 2 cells were calcium free during cell dissociation and for transport experiments, but not during cell loading (LC); and Group 3 cells were Ca free during cell dissociation, cell loading and transport experiments (WC). Intracellular Ca was recorded through time after ATP was added to the cells and ATP caused an increase in Ca efflux within 30s in all cells. WC cells showed the smallest Ca efflux compared to the other cells, probably because it was intracellularly Ca ""depleted"". Vanadate and amiloride decreased the Ca efflux when ATP was added to the cells, while verapamil did not cause any effect in Ca efflux, confirming the presence of a Ca(2+)-ATPase sensitive to vanadate in hepatopancreas of D. pagei. In a different set of experiments, cells were also exposed to a Ca pulse of 1 and 10mM during 180s. 10mM Ca increased intracellular Ca compared to 1mM, and the increase was not recovered during the experimental time. Additionally, Ca influx was reduced by verapamil and amiloride, but not completely. The results suggest that Ca influx probably occurs through an undefined exchanger, apart from Ca channels (verapamil sensitive) and electrogenic 1Na(+)(1H(+))/1 Ca(2+) exchanger (amiloride-sensitive). Similarities between freshwater and seawater crabs, lobsters and crayfish in relation to plasma membrane Ca transporters, although the environment where they live is quite diverse, suggest that universal mechanisms for Ca homeostasis are widespread among crustaceans. (C) 2010 Elsevier Inc. All rights reserved.

Direct action of aldosterone on bicarbonate reabsorption in in vivo cortical proximal tubule

Pergher PS, Leite-Dellova D, de Mello-Aires M. Direct action of aldosterone on bicarbonate reabsorption in in vivo cortical proximal tubule. Am J Physiol Renal Physiol 296: F1185-F1193, 2009. First published February 18, 2009; doi:10.1152/ajprenal.90217.2008.-The direct action of aldosterone (10(-12) M) on net bicarbonate reabsorption (J(HCO3)(-)) was evaluated by stationary microperfusion of an in vivo middle proximal tubule (S2) of rat kidney, using H ion-sensitive microelectrodes. Aldosterone in luminally perfused tubules caused a significant increase in J(HCO3)(-) from a mean control value of 2.84 +/- 0.08 [49/19 (n degrees of measurements/n degrees of tubules)] to 4.20 +/- 0.15 nmol.cm(-2).s(-1) (58/10). Aldosterone perfused into peritubular capillaries also increased J(HCO3)(-), compared with basal levels during intact capillary perfusion with blood. In addition, in isolated perfused tubules aldosterone causes a transient increase of cytosolic free calcium ([Ca(2+)](i)), monitored fluorometrically. In the presence of ethanol ( in similar concentration used to prepare the hormonal solution), spironolactone (10(-6) M, a mineralocorticoid receptor antagonist), actinomycin D (10(-6) M, an inhibitor of gene transcription), or cycloheximide (40 mM, an inhibitor of protein synthesis), the J(HCO3)(-) and the [Ca(2+)](i) were not different from the control value; these drugs also did not prevent the stimulatory effect of aldosterone on J(HCO3)(-) and on [Ca(2+)](i). However, in the presence of RU 486 alone [10(-6) M, a classic glucocorticoid receptor (GR) antagonist], a significant decrease on J(HCO3)(-) and on [Ca(2+)](i) was observed; this antagonist also inhibited the stimulatory effect of aldosterone on J(HCO3)(-) and on [Ca(2+)](i). These studies indicate that luminal or peritubular aldosterone (10(-12) M) has a direct nongenomic stimulatory effect on J(HCO3)(-) and on [Ca(2+)](i) in proximal tubule and that probably GR participates in this process. The data also indicate that endogenous aldosterone stimulates J(HCO3)(-) in middle proximal tubule.