State Of Ca2 Research Articles

Experimental Study on the Shear Strength of Loess Modified by Microbial Precipitation Technology

The shear strength (vertical pressure 50, 100, 200, and 300 kPa) and soil structure of the remolded loess with different proportions of the microbial cementing solution were measured and observed by the direct shear test and scanning electron microscopy (SEM).The results showed: (1) the increase in the microbial cementation solution led to the transformation of the stress-shear displacement curve from strain hardening to strain softening, with the transition interval of 26%∼34%. (2) With the increase in the microbial cementation solution, the change of cohesion showed a trend of “M,” the inflection point of the microbial cementation solution was 14%, 22%, and 34%, while the internal friction angle showed a law of “W,” where the inflection points of the internal friction angle were about 14%, 30%, 34%, and 38%, respectively. In the range of 18%∼30%, the cohesion and internal friction angle increase with an increase in the microbial cementation solution.(3) The change of cohesion is affected by the microbial mineralization saturation and the joint action of the occurrence state of Ca2+ and HCO3- in the microbial cementation solution. The change of internal friction angle is affected by the soil particle contact, the existing form of calcium carbonate formed by microbial precipitation, pore morphology, yield, and other forces. (4) By means of SEM, the distribution morphology of the soil particles and the contact microscopic images of the loess samples modified by microorganisms with different proportions were further verified to further verify the macroscopic changes of the shear strength of the modified loess samples cemented by microorganisms with different proportions. It provides a theoretical basis for the improvement of loess soil structure characteristics by microorganism calcium carbonate precipitation technology.

A Molecular Pinball Machine of the Plasma Membrane Regulates Plant Growth-A New Paradigm.

Novel molecular pinball machines of the plasma membrane control cytosolic Ca2+ levels that regulate plant metabolism. The essential components involve: 1. an auxin-activated proton pump; 2. arabinogalactan glycoproteins (AGPs); 3. Ca2+ channels; 4. auxin-efflux “PIN” proteins. Typical pinball machines release pinballs that trigger various sound and visual effects. However, in plants, “proton pinballs” eject Ca2+ bound by paired glucuronic acid residues of numerous glycomodules in periplasmic AGP-Ca2+. Freed Ca2+ ions flow down the electrostatic gradient through open Ca2+ channels into the cytosol, thus activating numerous Ca2+-dependent activities. Clearly, cytosolic Ca2+ levels depend on the activity of the proton pump, the state of Ca2+ channels and the size of the periplasmic AGP-Ca2+ capacitor; proton pump activation is a major regulatory focal point tightly controlled by the supply of auxin. Auxin efflux carriers conveniently known as “PIN” proteins (null mutants are pin-shaped) pump auxin from cell to cell. Mechanosensitive Ca2+ channels and their activation by reactive oxygen species (ROS) are yet another factor regulating cytosolic Ca2+. Cell expansion also triggers proton pump/pinball activity by the mechanotransduction of wall stress via Hechtian adhesion, thus forming a Hechtian oscillator that underlies cycles of wall plasticity and oscillatory growth. Finally, the Ca2+ homeostasis of plants depends on cell surface external storage as a source of dynamic Ca2+, unlike the internal ER storage source of animals, where the added regulatory complexities ranging from vitamin D to parathormone contrast with the elegant simplicity of plant life. This paper summarizes a sixty-year Odyssey.

Evidence for the Mn4-Yz[rad] Magnetic Interaction in Ca2+- depleted Photosystem II

The Photosystem II (PSII) water oxidation to molecular oxygen process is catalyzed by an oxygen-bridged Mn4CaO5 cluster, known as Oxygen Evolving Complex (OEC) of PSII. The Mn4CaO5 cluster undergoes periodically four one-electron oxidation steps, S0 → S1, S1 → S2, S2 → S3, S3 → S0. The O2 release takes place during the S3-[S4]-S0 transition, S4 being a transient. The intermediates of the S-state transitions are known as metalloradical intermediate states (SiYz) and involve the free radical of Tyrosine Z (Yz, TyrZ). In most metalloradical states it was established that Yz interacts magnetically with the Mn4CaO5 cluster. However, in Ca2+- depleted PSII preparations the spin-spin interaction between the Mn4O5 and Yz, during the formation of the S2Yz intermediate state was not strongly supported experimentally. In our effort to investigate the existence of the aforementioned interaction, we took advantance of the NIR sensitivity of the S2 state of Mn4 and examined whether the S2Yz EPR spectrum can be modified. Our EPR experiments, combined with the simulation analysis of the spectra show that reversible modification of the S2 EPR spectrum by NIR irradiation results in a reversible change of the Yz EPR signal shape. These observations strongly support the idea of the magnetic interaction between the Mn4 and tyrosyl radical, upon the formation of the S2Yz metalloradical state in Ca2+- depleted PSII membranes.

A novel stiffening factor inducing the stiffest state of holothurian catch connective tissue

The dermis of sea cucumbers is a catch connective tissue or mutable collagenous tissue that shows large changes in stiffness. Extensive studies on the dermis revealed that it can adopt three different states having different mechanical properties that can be reversibly converted. These are the stiff, standard and soft states. The standard state is readily produced when a dermal piece is immersed in the sea water containing Ca²+, whereas the soft state can be produced by removal of Ca²+. A stiffening protein, tensilin, has been isolated from some sea cucumbers (Cucumaria frondosa and Holothuria leucospilota). Although tensilin converts the state of the dermis from soft to standard, it cannot convert from standard to stiff. In this study, we isolated and partially purified a novel stiffening factor from the dermis of Holothuria leucospilota. The factor stiffened the dermis in normal artificial sea water (ASW) but did not stiffen the soft dermis in Ca²+-free ASW. It also stiffened the dermis that had been converted to the standard state in Ca²+-free ASW by the action of tensilin. These results suggest that the factor produces the stiff dermis from the standard state but cannot work as a stiffener on the soft dermis. Its addition to longitudinal muscles of the sea cucumber produced no effects, suggesting that its effect is specific to the catch connective tissue. Its stiffening activity was susceptible to trypsin, meaning that it is a polypeptide, and its molecular mass estimated from gel filtration chromatography was 2.4 kDa.

Involvement of calcium-independent phospholipase A2 in regulation of Ca2+ signals induced by a calmodulin inhibitor in rat thymocytes

Previous studies have shown that micromolar concentrations of calmodulin inhibitor calmidazolium induce fast activation of nonselective Ca2+ channels in plasma membranes of Ehrlich ascites carcinoma cells (Zinchenko, V.P., Kasymov, V.A., Li, V.V., and Kaimachnikov, N.P., Biofizika (Rus.), 2005, vol. 50 (6), pp. 1055–1069). In order to detect this type of Ca2+ channels in other cells and to establish common regulatory mechanisms, we studied calmidazolium effects on rat thymocytes. It was found that calmidazolium induces biphasic increases in Ca2+ content in cytosol of rat thymocytes due to Ca2+ entry from external medium and reflects the activity of nonselective Ca2+ channels permeable for Mn2+ and Ni2+ ions. The rate and the amplitude of the fast phase are decreased, while those of the slow phase are increased in the presence of specific inhibitors of Ca2+-independent phospholipase A2 (bromoenol lactone and palmitoyl trifluoromethyl ketone). The rate and the amplitude of the fast phase are also inhibited by arachidonic acid and the lipoxygenase inhibitor nordihydroguaiaretic acid, while the Ca2+-dependent phospholipase A2 inhibitor bromophenacyl bromide, the cyclooxygenase inhibitor indomethacin, the specific store-operated Ca2+ channel inhibitor gadolinium and the phospholipase C inhibitor U73122 have no such effect. The rate of the fast phase only slightly depends on temperature, while that of the slow phase shows a strong temperature dependence and increases with a rise in temperatures (Q10 = 2). The amplitude of the fast phase of the Ca2+ signal increases with a decrease of temperatures due to prolongation of the maximum activity of the Ca2+ channel. The data obtained suggest that iPLA2 is an intermediate link in the activation of calmidazolium-induced nonselective Ca2+ channels. The iPLA2 products lysophospholipids and arachidonic acid activate and inhibit Ca2+ channels, respectively. The fact that these compounds manifest different affinities for Ca2+ channels shed additional light on the mechanisms of biphasic Ca2+ elevation in thymus cell cytosol and prolongation of the active state of Ca2+ channels at low temperatures.

A new potential function form incorporating extended long-range behaviour: application to ground-state Ca2

A new analytic potential energy function form which incorporates the two leading inverse-power terms in the long-range potential is introduced and applied to a recently reported data set for the ground state of Ca2. The new function yields an accurate representation of data which span 99.97% of the well depth and involves only a fraction as many (between 1/3 and 2/3 fewer) parameters as were needed to define published potential functions for these systems based on the same data. Fits using this form also allow a robust determination of the dissociation energy and C 6 dispersion coefficient, and the resulting function is easier to use than other potential functions which have been determined for this system.

Targeted gene transfer increases contractility and decreases oxygen cost of contractility in normal rat hearts

The aim of this study was to examine how global cardiac gene transfer of sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a) can influence left ventricular (LV) mechanical and energetic function, especially in terms of O(2) cost of LV contractility, in normal rats. Normal rats were randomized to receive an adenovirus carrying the SERCA2a (SERCA) or beta-galactosidase (beta-Gal) gene or saline by a catheter-based technique. LV mechanical and energetic function was measured in cross-circulated heart preparations 2-3 days after the infection. The end-systolic pressure-volume relation was shifted upward, end-systolic pressure at 0.1 ml of intraballoon water volume was higher, and equivalent maximal elastance, i.e., enhanced LV contractility, was higher in the SERCA group than in the normal, beta-Gal, and saline groups. Moreover, the LV relaxation rate was faster in the SERCA group. There was no significant difference in myocardial O(2) consumption per beat-systolic pressure-volume area relation among the groups. Finally, O(2) cost of LV contractility was decreased to subnormal levels in the SERCA group but remained unchanged in the beta-Gal and saline groups. This lowered O(2) cost of LV contractility in SERCA hearts indicates energy saving in Ca(2+) handling during excitation-contraction coupling. Thus overexpression of SERCA2a transformed the normal energy utilization to a more efficient state in Ca(2+) handling and superinduced the supranormal contraction/relaxation due to enhanced Ca(2+) handling.

The critical role of the proximal calcium ion in the structural properties of horseradish peroxidase.

The extent to which the structural Ca(2+) ions of horseradish peroxidase (HRPC) are a determinant in defining the heme pocket architecture is investigated by electronic absorption and resonance Raman spectroscopy upon removal of one Ca(2+) ion. The Fe(III) heme states are modified upon Ca(2+) depletion, with an uncommon quantum mechanically mixed spin state becoming the dominant species. Ca(2+)-depleted HRPC forms complexes with benzohydroxamic acid and CO which display spectra very similar to those of native HRPC, indicating that any changes to the distal cavity structural properties upon Ca(2+) depletion are easily reversed. Contrary to the native protein, the Ca(2+)-depleted ferrous form displays a low-spin bis-histidyl heme state and a small proportion of high-spin heme. Furthermore, the nu(Fe-Im) stretching mode downshifts 27 cm(-1) upon Ca(2+) depletion revealing a significant structural perturbation of the proximal cavity near the histidine ligand. The specific activity of the Ca(2+)-depleted enzyme is 50% that of the native form. The effects on enzyme activity and spectral features observed upon Ca(2+) depletion are reversible upon reconstitution. Evaluation of the present and previous data firmly favors the proximal Ca(2+) ion as that which is lost upon Ca(2+) depletion and which likely plays the more critical role in regulating the heme pocket structural and catalytic properties.

Surface Exposure of the Methionine Side Chains of Calmodulin in Solution: A NITROXIDE SPIN LABEL AND TWO-DIMENSIONAL NMR STUDY

Binding of calcium to calmodulin (CaM) causes a conformational change in this ubiquitous calcium regulatory protein that allows the activation of many target proteins. Met residues make up a large portion of its hydrophobic target binding surfaces. In this work, we have studied the surface exposure of the Met residues in the apo- and calcium-bound states of CaM in solution. Complexes of calcium-CaM with synthetic peptides derived from the CaM-binding domains of myosin light chain kinase, constitutive nitric-oxide synthase, and CaM-dependent protein kinase I were also studied. The surface exposure was measured by NMR by studying the effects of the soluble nitroxide spin label, 4-hydroxyl-2,2,6, 6-tetramethylpiperidinyl-1-oxy, on the line widths and relaxation rates of the Met methyl resonances in samples of biosynthetically 13C-methyl-Met-labeled CaM. The Met residues move from an almost completely buried state in apo-CaM to an essentially fully exposed state in Ca2+4-CaM. Binding of two Ca2+ to the C-terminal lobe of CaM causes full exposure of the C-terminal Met residues and a partial exposure of the N-terminal Met side chains. Binding of the three target peptides blocks the access of the nitroxide surface probe to nearly all Met residues, although the mode of binding is distinct for the three peptides studied. These data show that calcium binding to CaM controls the surface exposure of the Met residues, thereby providing the switch for target protein binding.

Effect of Korean red ginseng on the rabbit corpus cavernosal smooth muscle.

The extracts of Korean red ginseng (EKG) is a complex mixture containing ginsenosides, polysaccharides, and several other products. Animal experiments have shown that the intravenous administration of extract of ginseng reduces blood pressure. Recently, it has been reported that ginseng has a relaxing effect on vascular smooth muscle and that the relaxation is associated with nitric oxide (NO) released from the vascular endothelium. The present study was undertaken to investigate the effects of EKG on isolated rabbit corpus cavernosal smooth muscle for evaluation of the possibility of developing EKG as an pharmacoerecting agent. Strips of rabbit corpus cavernosum were mounted in organ chambers to measure isometric tension. On the precontracted muscle strip with phenylephrine (PHE; 5 x 10(-6) M), EKG began to exert a relaxing effect at the concentration of 1 mg/ml and the maximal relaxation effect was reached at 40 mg/ml in a dose-dependent manner. EKG was inhibited significantly by endothelial disruption and by pretreatment with methylene blue, pyrogallol, L-NNA or atropine. EKG partially inhibited the PHE (5 x 10(-6) M) induced contraction up to 45.67% of the control in a dose-dependent fashion. EKG decreased basal tension as well as inhibited the contraction induced by addition of CaCl2 (10(-3) M) dose-dependently in muscle strips at basal equilibrated state in Ca2+ free, high K+ depolarizing solution. EKG also inhibited the contraction induced by depolarization with 20, 40 and 60 mM of KCl. However, this inhibitory effect did not occur with high concentrations of KCl (80 and 120 mM). EKG has a relaxing effect on the rabbit corpus cavernosal tissue in a dose dependent manner. The relaxation action of EKG is mediated by multiple action mechanisms that include increasing the release of NO from the corporal sinusoids, increasing intracellular calcium sequestration, and a hyperpolarizing action.

Calcium oscillations in parotid acinar cells induced by microsomal Ca(2+)-ATPase inhibition.

Previous studies have demonstrated in single rat parotid acinar cells that the microsomal Ca(2+)-ATPase inhibitor thapsigargin mobilizes Ca2+ specifically from the inositol 1,4,5-trisphosphate (IP3)-sensitive Ca2+ store, activates plasma membrane Ca2+ permeability, and induces intracellular Ca2+ concentration ([Ca2+]i) oscillations that are quite similar to those activated by carbachol. Nevertheless, the IP3-sensitive Ca2+ store remains continuously depleted during thapsigargin-induced oscillations, indicating that this pool is not involved in the oscillation mechanism. To determine the specificity of thapsigargin's effects, in the present study we have examined the effects on [Ca2+]i in single rat parotid acinar cells of two other microsomal Ca(2+)-ATPase inhibitors, cyclopiazonic acid (CPA) and 2,5-di-tert-butyl-1,4-benzohydroquinone (BHQ), and compared them with the effects of thapsigargin in the same cells. Our results demonstrate that thapsigargin, CPA, and BHQ all similarly deplete the IP3-sensitive Ca2+ store specifically, activate plasma membrane Ca2+ influx, and induce [Ca2+]i oscillations, strongly suggesting that these agents have a specific inhibitory action on microsomal Ca(2+)-ATPase activity. BHQ, in addition, inhibits plasma membrane Ca2+ influx. The data lend strong support to a model in which the state of Ca2+ filling of the IP3-sensitive store regulates plasma membrane Ca2+ influx. These results suggest either that a Ca2+ pump is involved which is insensitive to structurally dissimilar inhibitors or that a Ca2+ pump is not involved in refilling of the Ca2+ pool involved in [Ca2+]i oscillations in these cells.

Multiple forms of vitamin D-dependent calcium-binding protein in rat kidney.

The technique of two-dimensional electrophoresis was used in combination with a highly sensitive silver stain to study vitamin D-dependent calcium-binding protein (CaBP) in rat kidney. Rat renal CaBP was shown to co-migrate almost exactly with CaBP purified from chick intestine suggesting evolutionary conservation of this protein. In some cases rat renal CaBP appeared not as a single polypeptide, but rather as a cluster of 4 polypeptides. Formation of the satellite cluster of CaBP in response to high doses of 1,25-dihydroxyvitamin D3 occurred in young rats which had been maintained on a vitamin D-deficient diet for 2 weeks, as well as in older rats which had been maintained on the same diet for 5 months. The 4 forms of CaBP were not the result of various states of Ca2+ binding, but rather the result of an enzymatic reaction. This was shown by 3 experiments. 1) Adding excess EGTA to samples containing the 4 satellite forms did not change the two-dimensional electrophoretogram. 2) Incubation of purified chick intestinal CaBP with kidney cytosols from D-deficient rats brought about the formation of the satellite CaBP forms from the chick protein. However, purified chick CaBP was unchanged by incubation in buffer alone for up to 2 h at 37 degrees C. 3) Placing rat kidney cytosols in a boiling water bath for 10 min inactivated the factor which generated the satellite forms as would be expected for an enzyme. The physiological significance of these forms of CaBP is as yet unknown.

Dissociation of phosphorylase a activation and contractile activity in rat portal vein.

Isometric force, glycogen phosphorylase activity and lactate production were measured under conditions known to alter intracellular Ca2+ and cAMP to assess the role of these messengers in the coordination of metabolism with contractility in rat portal vein. Total phosphorylase (a + b) activity, was independent of treatment. The activity ratio phosphorylase activity ratio in the presence of isoproterenol and papaverine was dependent on or high-K+ medium, and 0.57 after 20 min treatment with 10(-5) M isoproterenol + 10(-4) M papaverine. Under both of these conditions the muscle was totally relaxed. The phosphorylase activity ratio in the presence of isoproterenol and papaverine was dependent on extracellular Ca2+, both in normal and depolarizing medium. This suggests a lower Ca2+ sensitivity of the contractile than the phosphorylase system under these conditions, known to be associated with raised intracellular cAMP. During spontaneous activity and high-K+ induced contractures phosphorylase activity was increased compared to the relaxed state in Ca2+-free medium. A high level of phosphorylase activity (0.48) was elicited by the addition of 300 mM sucrose, which induces a contracture in Ca2+-free medium. Lactate production was in general parallel to phosphorylase activity, except for a relative increase in anoxia. The results suggest that in the intact cell the Ca2+-mediated linkage of contraction and phosphorylase may be modified by cAMP changing the Ca2+ sensitivities of the two systems in opposite directions.

The State of Accumulated Calcium in Mouse Brain Microsomes In Vitro1

The state of Ca2+ accumulated in mouse brain microsomes in the presence of ATP was investigated using three methods; the Ca2+ selectrode method, the continuous perfusion method and Millipore filtration. With the Ca2+ selectrode method, it appeared that the mechanism of ATP-dependent Ca2+ uptake consists of a Ca2+ transport step and a Ca2+ storage step. It was confirmed by continuous perfusion experiments that (a accumulated in the presence of ATP may be classified into two types, designated as Ca2+-type I and C2+-type II. Ca2+-type I is slowly released on perfusion of cations. On the other hand, Ca2+-type II remains unaffected by perfusion of cations and exchanges with Ca2+ added to the perfusion solution only if ATP is present in the solution. Sudden release of accumulated ( (Ca2+ II) occurred on treatments with 0.1% DOC, 0.5% Triton X-100, and 0.1 N HCl, but on treatment with 2mM EGTA, a specific chelator for Ca2+ no efflux of Ca2+-type II was observed. From the results obtained, it was concluded that the sites responsible for Ca2+-type II accumulated in the presence of ATP are clearly distinguishable from ion exchange-type cation binding sites. We propose the existence of other cation binding sites in brain microsomes, with the following properties: (i) in the presence of ATP, Ca2+ in the medium can penetrate to the sites, but in the absence of ATP, no cations (Mg2+ Ca2+ Na+, K+etc.) can enter the sites; (ii) the intact structure of the binding sites is readily disrupted by treatment with detergents. A model for ATP-dependent Ca2+ uptake in brain microsomesis proposed.