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Wang XH, Guo YW, Tolba E, Kokkinopoulou M, Wiens M, Schröder HC, Müller WEG. Two-Armed Activation of Bone Mineral Deposition by the Flavones Baicalin and Baicalein, Encapsulated in Polyphosphate Microparticles. THE AMERICAN JOURNAL OF CHINESE MEDICINE 2017; 45:533-555. [PMID: 28367715 DOI: 10.1142/s0192415x1750032x] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
In this study, we investigated the effect of the two flavonoids, baicalin (baicalein 7-O-[Formula: see text]- d-glucuronic acid) and its aglycone, baicalein (5,6,7-trihydroxyflavone), after encapsulation into amorphous calcium polyphosphate (Ca-polyP) microparticles on mineralization of primary human osteoblasts (phOSB). Both flavonoids, which come from root extracts of Scutellaria baicalensis Georgi, are used in Traditional Chinese Medicine, and are nontoxic in cells up to a concentration of 3[Formula: see text][Formula: see text]g/ml. The morphogenetically active, energy-rich Ca-polyP particles with a stoichiometric P:Ca ratio of 1:2 are degraded by cellular alkaline phosphatase (ALP) to ortho-phosphate used for bone hydroxyapatite formation. Here we show that the flavone-loaded Ca-polyP microparticles are readily taken up by phOSB, resulting in the accumulation of polyP around the nuclei and the formation of intracellular vesicles containing the ALP. In addition, we demonstrate that baicalin/baicalein causes a rise of the intracellular calcium [Ca[Formula: see text]]i a level which markedly is augmented after encapsulation into Ca-polyP, through activation of the phospholipase C. Moreover, both flavones, either alone or associated with Ca-polyP microparticles, upregulate the expression of the osteoblast calcium efflux channel, the plasma membrane Ca[Formula: see text]-ATPase (PMCA), while the expression of ALP, which promotes bone mineralization, is induced by Ca-polyP and by the flavones only if present in the Ca-polyP-microparticle-associated form. As a result, the extent of bone mineralization is markedly enhanced. Based on the two-armed activating function, new applications of baicalin/baicalein as a component of nutriceuticals for osteoporosis prevention or bone implants can be envisaged.
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Affiliation(s)
- Xiao-Hong Wang
- * ERC Advanced Investigator Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, D-55128 Mainz, Germany
| | - Yue-Wei Guo
- † State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
| | - Emad Tolba
- * ERC Advanced Investigator Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, D-55128 Mainz, Germany
| | | | - Matthias Wiens
- * ERC Advanced Investigator Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, D-55128 Mainz, Germany
| | - Heinz C Schröder
- * ERC Advanced Investigator Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, D-55128 Mainz, Germany
| | - Werner E G Müller
- * ERC Advanced Investigator Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, D-55128 Mainz, Germany
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Rodan GA, Heath JK, Yoon K, Noda M, Rodan SB. Diversity of the osteoblastic phenotype. CIBA FOUNDATION SYMPOSIUM 2007; 136:78-91. [PMID: 3068018 DOI: 10.1002/9780470513637.ch6] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Studies of bone cells in culture have raised two salient questions: are the findings representative of the in vivo situation and can the conflicting data from different cell models be reconciled? Review of the literature indicates that all osteoblastic cells, defined by their origin or by their ability to produce mineralized matrix, have a few common properties: production of type I collagen; increased alkaline phosphatase activity; and parathyroid hormone-stimulated adenylate cyclase. Other features, such as osteocalcin and prostaglandin E production and the response to prostaglandin E, are selectively expressed by certain cell types. Pilot studies on mRNA levels of 'bone proteins' in developing calvaria suggest that such differences may reflect stages in osteoblastic differentiation. Immortalization of calvaria-derived cells using a SV40 large T antigen vector, which may freeze the cells in their particular state of differentiation (as proposed for leukaemia cells), yields phenotypes consistent with that hypothesis. Immortal cell lines may thus help to characterize osteoblastic differentiation. The diversity of osteoblast responses in culture to hormones and growth factors could be due to these phenotype differences but could also represent a subspecialization of differentiated cells. In addition, in the organism regulatory agents act in concert on a heterogeneous interactive cell population. Nonetheless cell cultures can be useful in screening for and predicting in vivo responses, as was shown by the 1,25-(OH)2D3 stimulation of osteocalcin, and for studying the molecular mechanisms of regulatory effects. Cell lines are also convenient for the production of specific proteins and cDNA libraries, and for the expression of specific genes.
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Affiliation(s)
- G A Rodan
- Department of Bone Biology, Merck Sharp and Dohme Research Laboratories, West Point, Pennsylvania 19486
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Stains JP, Weber JA, Gay CV. Expression of Na+/Ca2+ exchanger isoforms (NCX1 and NCX3) and plasma membrane Ca2+ ATPase during osteoblast differentiation. J Cell Biochem 2002. [DOI: 10.1002/jcb.10050] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Stains JP, Gay CV. Inhibition of Na+/Ca2+ exchange with KB-R7943 or bepridil diminished mineral deposition by osteoblasts. J Bone Miner Res 2001; 16:1434-43. [PMID: 11499866 DOI: 10.1359/jbmr.2001.16.8.1434] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Osteoblasts form new bone by secreting a complex extracellular matrix that has the capacity to mineralize when adequate amounts of calcium and phosphate are supplied. The studies reported here show that long-term treatment of cultured, primary osteoblasts with Na+/Ca2+ exchanger (NCX) inhibitors, bepridil and KB-R7943, impacts in a dose-dependent manner the ability of the cells to form a calcified matrix. Treatment of confluent osteoblast cultures for 14 days with low levels of bepridil (3.0 microM) or KB-R7943 (1.0 microM and 0.1 microM) resulted in a significantly diminished capacity of these cells to mineralize bone matrix, without significantly altering cell morphology, viability, or cell differentiation. The data indicate that inhibition of NCX reduces mineral accumulation in the bone matrix by blocking the efflux of Ca2+ from the osteoblast into the bone fluid. In addition, immunocytochemistry of type I collagen (COLI) and bone sialoprotein (BSP) suggests that inhibition of NCX by 1.0 microM KB-R7943 also may impair the secretion of bone matrix proteins by the osteoblasts. This study is the first to show that NCX is an important regulator of the bone fluid microenvironment and that NCX appears critical to the mineralization process.
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Affiliation(s)
- J P Stains
- Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, USA
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Gay CV, Lloyd QP. Characterization of calcium efflux by osteoblasts derived from long bone periosteum. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. PART A, PHYSIOLOGY 1995; 111:257-61. [PMID: 7669110 DOI: 10.1016/0300-9629(95)00004-q] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Inside-out vesicles were prepared from the plasma membrane of osteoblasts which had been isolated from the periosteum of 2-3-week-old chicken tibia and cultured for 6-8 days. Calcium uptake was initiated by adding 0.4 mM ATP and detected as a reduction in fluorescence from the reaction medium using the Ca(2+)-specific fluoroprobe, fluo-3. The reaction medium contained ouabain (1 mM) to block Na+, K(+)-ATPase activity and oligomycin (20 micrograms/ml) to block mitochondrial activity. Thapsigargin (5 microM) had little effect, indicating that contributions to Ca2+ uptake by endoplasmic reticulum derived microsomes were minimal. The Ca2+ uptake rate was 9.9 +/- 2.3 nmol/mg protein/min. Trifluoperazine (0.1 mM), which impairs the capacity of calmodulin to activate Ca(2+)-ATPase, substantially inhibited transport, as did quercetin (10 mM) and vanadate (10 microM), inhibitors of Ca(2+)-ATPases. This study has shown the presence of an outwardly directed, calmodulin-sensitive calcium transport system in the primary osteoblast plasma membrane. The pumping rate is substantially less than rates found in the intestine, a tissue which is involved in massive transport of Ca2+, but is similar to rates found in many other tissues. It is concluded that the enzyme does not support calcium translocation to sites of mineralization.
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Affiliation(s)
- C V Gay
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park 16802, USA
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Abstract
We report here that osteoblasts and osteoblast-like osteosarcoma cells express PMCA1b, an alternatively spliced transcript of plasma membrane Ca(2+)-ATPase. Synthetic oligonucleotide pairs were designed based upon unique regions of the cDNA encoding known PMCA isoforms (PMCA1-3) and used as primers in PCR-mediated amplification of cDNA synthesized from ROS 17/2.8 osteosarcoma cell RNA. A product was observed only when PMCA1-specific primers were present; no products were seen with PMCA2 or PMCA3 primers unless cDNA synthesized from rat brain RNA was present. Examination of the cDNA encoding the C terminus of PMCA1 from ROS 17/2.8 cells revealed that the mRNA is spliced to yield the PMCA1b isoform, a Ca(2+)-ATPase containing a consensus phosphorylation site for cAMP-dependent protein kinase A and a modified calmodulin binding domain. PMCA1b was also detected in UMR-106-01 osteosarcoma cells and unpassaged primary rat calvarial osteoblasts. These results suggest that the regulation of osteoblast function by agents that act via cAMP-mediated pathways may involve alterations in the activity of the plasma membrane Ca(2+)-ATPase.
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Affiliation(s)
- J G Meszaros
- Department of Physiology and Cell Biology, University of Texas Medical School, Houston
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Abstract
The plasma membrane fraction of chicken osteoclasts was purified utilizing 20% continuous Percoll gradients. Biochemical marker enzyme analysis (ouabain-sensitive Na+,K(+)-ATPase and 5'-nucleotidase) indicated that plasma membrane enrichment was 11.87-fold and 7.25-fold, respectively, and contamination with mitochondria, endoplasmic reticulum, and lysosomes was low as determined by succinic dehydrogenase, NADH dehydrogenase, and N-acetylglucosaminidase activities, respectively. SDS latency of Na+,K(+)-ATPase and 5'-nucleotidase activities of the isolated plasma membranes revealed that 43-50% of vesicles were sealed, with 10-16% in the inside-out orientation, depending on the membrane fraction used. Electron microscopy confirmed the vesicular nature of the plasma membrane fraction. The plasma membrane Ca2(+)-ATPase had a high-affinity (KCa = 0.22 microM; Vmax = 0.16 mumol/mg per min) and a low-affinity (KCa = 148 microM; Vmax = 0.37 mumol/mg per min) component. Calmodulin (0.12 microM) had no effect on Ca2(+)-ATPase activity. However, trifluoperazine (0.1 mM), a calmodulin antagonist, strongly inhibited especially the high-affinity component of the enzyme. Vanadate and lanthanum also caused inhibition. In the presence of CDTA, a potent Ca2+ and Mg2+ chelating agent, high-affinity Ca2(+)-ATPase activity was abolished, indicating that trace Mg2+ was essential for activity. The Ca2(+)-ATPase substrate curve using ATP showed a high-affinity (Km = 12.3 microM; Vmax = 0.022 mumol/mg per min) and a low-affinity (Km = 43.8 microM; Vmax = 0.278 mumol/mg per min) component. These results demonstrate that osteoclasts have a plasma membrane Ca2(+)-ATPase with characteristics similar to the enzyme responsible for active calcium extrusion in other cells.
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Affiliation(s)
- P J Bekker
- Department of Molecular and Cell Biology, Pennsylvania State University, University Park 16802
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Kelley LK, Borke JL, Verma AK, Kumar R, Penniston JT, Smith CH. The calcium-transporting ATPase and the calcium- or magnesium-dependent nucleotide phosphatase activities of human placental trophoblast basal plasma membrane are separate enzyme activities. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)39382-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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Akisaka T, Yamamoto T, Gay CV. Ultracytochemical investigation of calcium-activated adenosine triphosphatase (Ca++-ATPase) in chick tibia. J Bone Miner Res 1988; 3:19-25. [PMID: 2975140 DOI: 10.1002/jbmr.5650030105] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The ultrastructural distribution of Ca++-ATPase in bone cells of growing chick tibia was investigated by a cytochemical method in order to gain insight into possible sites of calcium ion translocation. Both osteoclasts and osteoblasts showed a polar distribution of reaction product along the plasma membrane. In osteoclasts, enzymatic activity occurred along the portion of the plasma membrane facing the marrow but not along the ruffled border or clear zone. The reaction product in these cells was due solely to Ca++-ATPase action. In osteoblasts, the plasma membrane facing away from bone (apical and lateral membrane) was very intensely stained, whereas the basal membrane was unstained. The reaction product in these cells appeared to be the result of both Ca++-ATPase and Ca++,Mg++-ATPase. In osteocytes, no plasma membrane staining was detectable. Mitochondrial staining in all three types of cells was more sensitive to fixation than was the plasma membrane enzyme, suggesting that mitochondrial and plasma membrane Ca++-ATPases are chemically distinct, as biochemical studies have shown. In general, mitochondria in osteoclasts stained more intensely than those in osteoblasts or osteocytes. Mitochondrial and vesicular sites of activity may be related to intracellular calcium storage, whereas calcium ATPases of the plasma membrane are presumed to be involved in calcium efflux from the cells. Calcitonin treatment did not alter the enzymatic distribution or intensity in osteoclasts. The striking polar distribution of both osteoclast and osteoblast plasma-membrane activity suggests that directional calcium pumping by these cells may be of importance in bone-forming and bone-resorbing mechanisms.
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Affiliation(s)
- T Akisaka
- Molecular and Cell Biology Program, Pennsylvania State University, University Park 16802
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Sauer G, Watabe N. The effects of heavy metals and metabolic inhibitors on calcium uptake by gills and scales of Fundulus heteroclitus in vitro. ACTA ACUST UNITED AC 1988. [DOI: 10.1016/0742-8413(88)90062-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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Abstract
A high affinity, calmodulin-sensitive (Ca2 + Mg2+)-ATPase was demonstrated in the plasma membrane preparation of three different osteosarcoma cell lines previously demonstrated to respond to parathyroid hormone with an increase in cytosolic calcium and a decrease in pH. The maximal velocity of the enzyme activity in the membrane preparations ranged from 0.83 to 2.42 nmol Pi released per min per mg protein with half-saturation constants of 26 nM of free Ca. The enzyme activity was not affected by Na+, K+, ouabain and azide, and exhibited an absolute requirement for Mg2+ ions. These results suggest a possible role for a membrane Ca2 + Mg2+-ATPase in initiating and perpetuating the ionic control of osteoblastic function.
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Affiliation(s)
- V Shen
- Division of Bone and Mineral Disease, Washington University School of Medicine, St. Louis, MO
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Koh E, Morimoto S, Fukuo K, Shiraishi T, Hironaka T, Onishi T, Kumahara Y. Effects of nitrates and calcium channel blockers on Ca2+-ATPase in the microsomal fraction of porcine coronary artery smooth muscle cells. Cell Calcium 1987; 8:397-410. [PMID: 2962738 DOI: 10.1016/0143-4160(87)90014-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
The effects of the antianginal drugs nitroglycerin, nicorandil, diltiazem, verapamil and nicardipine on the activity of calcium-stimulated magnesium-dependent ATPase (Ca2+-ATPase) were investigated in the microsomal fraction from porcine coronary artery smooth muscle cells. Two discrete Ca2+-dependent ATPase components were observed: [1] a high affinity component, which was a specific Ca2+-ATPase, [with a half saturation constant for Ca2+ (Km) of 0.44 microM, and maximum velocity (Vmax) of 124.3 pmol of phosphate (Pi) released/micrograms of protein/30 min]: [2] a low affinity component in which Ca2+ could be replaced by Mg2+ without loss of its activity. Nitroglycerin and nicorandil (1 microM and 10 microM) both stimulated the activity of the Ca2+-ATPase significantly [142 +/- 12 (mean +/- standard error), and 137 +/- 10% of the control with nitroglycerin, and 152 +/- 17 and 135 +/- 20% with nicorandil] at a Ca2+ concentration of 0.3 microM. Diltiazem, verapamil and nicardipine did not cause significant stimulation. Nitroglycerin and nicorandil (1 microM), significantly decreased the Km for Ca2+ from the control value of 0.44 +/- 0.06 microM to 0.26 +/- 0.03 and 0.22 +/- 0.03 microM, respectively. Nitroglycerin and nicorandil may dilate coronary arteries by stimulating this Ca2+ extrusion pump enzyme through reduction of intracellular Ca2+ in smooth muscle cells.
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Affiliation(s)
- E Koh
- Department of Medicine, Osaka University Medical School, Japan
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Minami J, Penniston JT. Ca2+ uptake by corpus-luteum plasma membranes. Evidence for the presence of both a Ca2+-pumping ATPase and a Ca2+-dependent nucleoside triphosphatase. Biochem J 1987; 242:889-94. [PMID: 3036105 PMCID: PMC1147792 DOI: 10.1042/bj2420889] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Plasma-membrane vesicles from rat corpus luteum showed an ATP-dependent uptake of Ca2+. Ca2+ was accumulated with a K1/2 (concn. giving half-maximal activity) of 0.2 microM and was released by the bivalent-cation ionophore A23187. A Ca2+-dependent phosphorylated intermediate (Mr 100,000) was detected which showed a low decomposition rate, consistent with it being the phosphorylated intermediate of the transport ATPase responsible for Ca2+ uptake. The Ca2+ uptake and the phosphorylated intermediate (E approximately P) displayed several properties that were different from those of the high-affinity Ca2+-ATPase previously observed in these membranes. Both Ca2+ uptake and E approximately P discriminated against ribonucleoside triphosphates other than ATP, whereas the ATPase split all the ribonucleoside triphosphates equally. Both Ca2+ uptake and E approximately P were sensitive to three different Hg-containing inhibitors, whereas the ATPase was inhibited much less. Ca2+ uptake required added Mg2+ (Km = 2.2 mM), whereas the ATPase required no added Mg2+. The maximum rate of Ca2+ uptake was about 400-fold less than that of ATP splitting; under different conditions, the decomposition rate of E approximately P was 1,000 times too slow to account for the ATPase activity observed. All of these features suggested that Ca2+ uptake was due to an enzyme of low activity, whose ATPase activity was not detected in the presence of the higher-specific-activity Ca2+-dependent ATPase.
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Hipkiss JB, Branford White CJ, Peters TJ. Effect of phenothiazines on Hymenolepis diminuta with special reference to the brush border Ca2+-dependent ATPase. Mol Biochem Parasitol 1987; 22:55-63. [PMID: 2949149 DOI: 10.1016/0166-6851(87)90069-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Incubation of Hymenolepis diminuta with the calmodulin antagonist trifluoperazine causes lesions in the brush border of the cestode. Exposure to a phenothiazine of lower lipophilicity, trifluoperazine sulphoxide, had little effect. Characterisation of isolated brush border revealed two forms of Ca2+-ATPase which exhibited maximum activity at pH 5.5 and 7.5. Both forms were Ca2+-dependent but only the latter was influenced by calmodulin and trifluoperazine. It is suggested that the Ca2+-ATPase present in the tapeworm brush border may be the site of trifluoperazine toxicity.
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Pekovic S, Nikezic G, Horvat A, Metlas R. A high affinity calcium-stimulated ATPase in synaptic plasma membranes detectable in the presence and absence of exogenous magnesium. Brain Res 1986; 379:251-6. [PMID: 2427164 DOI: 10.1016/0006-8993(86)90778-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
A Ca2+-stimulated ATPase activity detectable in the presence of submicromolar free Ca2+ was characterized in synaptic plasma membrane preparations. In the absence of exogenous magnesium, Ca2+-stimulated ATPase showed a K0.5 Ca2+ of 0.1 microM, Vmax of 125 nmol Pi/mg per min and a Hill number of 1.2. The addition of 1 mM MgCl2 increased basal ATPase activity by about 10-fold. After this activity had been subtracted, apparent values for Ca2+-stimulated ATPase were 0.033 microM (K0.5 Ca2+), 172 nmol Pi/mg per min (Vmax) with a Hill number of 4. These activities were non-significantly affected by ouabain, sodium azide, theophylline and sodium fluoride. The results obtained indicated that high affinity Ca2+-stimulated ATPase activity could be in synaptic plasma membrane-enriched fraction detected both in the presence and absence of exogenous magnesium. Furthermore, the data indicated that magnesium was required for calcium transport.
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McLaughlin J. A high affinity Ca2+-dependent ATPase in the surface membrane of the bloodstream stage of Trypanosoma rhodesiense. Mol Biochem Parasitol 1985; 15:189-201. [PMID: 3159962 DOI: 10.1016/0166-6851(85)90119-7] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Addition of Ca2+ (0.01-1 mM) to a standard Trypanosoma rhodesiense Mg2+-ATPase assay failed to elicit any increase in activity. However, in the absence of externally added Mg2+ and using calcium-EGTA or calcium-CDTA to precisely maintain free metal ion concentration, it was possible to measure a specific Ca2+-ATPase. Cell fractionation studies revealed this ATPase to be predominantly associated with subcellular particles having an equilibrium density of 1.22 g cm-3 and identified as surface membrane. Using a discontinuous sucrose gradient, a surface membrane enriched (SME) fraction, only slightly contaminated with mitochondria as judged by dichlorophenolindophenol-linked alpha-glycerophosphate dehydrogenase activity, was prepared. The SME fraction exhibited Ca2+-ATPase activity, using 200 nM free Ca2+, of 90 and 21 mU mg-1 protein, respectively, using CDTA and EGTA as buffering ligands. This latter result was most unexpected and indicated that the Ca2+-ATPase, in addition to having no Mg2+ requirement, was inhibited by submicromolar levels of Mg2+. The Ca2+-ATPase was found to have a K0.5 = 128 +/- 22 nM free Ca2+, the response to increasing Ca2+ concentration displaying an extremely high degree of co-operativity (Hill number (nH) = 4.9). The enzyme was found to be highly substrate-specific for ATP with K0.5 = 6.2 +/- 0.61 microM ATP. A Hill plot of the reaction velocity as a function of ATP concentration indicated two substrate binding sites (nH = 1.55). A range of potential modulators of ATPase activity were investigated, with only vanadate (V2O3-8) having any effect: 47% inhibition at 5.0 microM. The Ca2+-ATPase was unaffected by the calmodulin antagonists chlorpromazine (50 microM) and trifluoperazine (50 microM), whilst addition of calmodulin failed to produce any stimulation of activity. It is concluded that the kinetic properties of this ATPase are compatible with a potential role in the regulation of intracellular Ca2+ in bloodstream T. rhodesiense.
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NANDI JYOTIRMOY, RAY TUSHARK. Evidence for Distinct Ca2+-ATPase Activities in Gastric Microsomes. Ann N Y Acad Sci 1984. [DOI: 10.1111/j.1749-6632.1984.tb13765.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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18
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Characterization of a Ca2+-stimulated Mg2+-dependent adenosine triphosphatase in Friend murine erythroleukemia cell plasma membranes. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(18)89820-9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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19
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Ansah TA, Molla A, Katz S. Ca2+-ATPase activity in pancreatic acinar plasma membranes. Regulation by calmodulin and acidic phospholipids. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(18)90714-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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20
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Tuan RS, Knowles KA. Calcium-activated ATPase of the chick embryonic chorioallantoic membrane. Identification, developmental expression, and topographic relationship with calcium-binding protein. J Biol Chem 1984. [DOI: 10.1016/s0021-9258(17)43210-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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