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Ismatullah H, Jabeen I, Kiani YS. Structural and functional insight into a new emerging target IP 3R in cancer. J Biomol Struct Dyn 2024; 42:2170-2196. [PMID: 37070253 DOI: 10.1080/07391102.2023.2201332] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2023] [Accepted: 04/05/2023] [Indexed: 04/19/2023]
Abstract
Calcium signaling has been identified as an important phenomenon in a plethora of cellular processes. Inositol 1,4,5-trisphosphate receptors (IP3Rs) are ER-residing intracellular calcium (Ca2+) release channels responsible for cell bioenergetics by transferring calcium from the ER to the mitochondria. The recent availability of full-length IP3R channel structure has enabled the researchers to design the IP3 competitive ligands and reveal the channel gating mechanism by elucidating the conformational changes induced by ligands. However, limited knowledge is available for IP3R antagonists and the exact mechanism of action of these antagonists within a tumorigenic environment of a cell. Here in this review a summarized information about the role of IP3R in cell proliferation and apoptosis has been discussed. Moreover, structure and gating mechanism of IP3R in the presence of antagonists have been provided in this review. Additionally, compelling information about ligand-based studies (both agonists and antagonists) has been discussed. The shortcomings of these studies and the challenges toward the design of potent IP3R modulators have also been provided in this review. However, the conformational changes induced by antagonists for channel gating mechanism still display some major drawbacks that need to be addressed. However, the design, synthesis and availability of isoform-specific antagonists is a rather challenging one due to intra-structural similarity within the binding domain of each isoform. HighlightsThe intricate complexity of IP3R's in cellular processes declares them an important target whereby, the recently solved structure depicts the receptor's potential involvement in a complex network of processes spanning from cell proliferation to cell death.Pharmacological inhibition of IP3R attenuates the proliferation or invasiveness of cancers, thus inducing necrotic cell death.Despite significant advancements, there is a tremendous need to design new potential hits to target IP3R, based upon 3D structural features and pharmacophoric patterns.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Humaira Ismatullah
- Department of Sciences, School of Interdisciplinary Engineering and Sciences (SINES), National University of Sciences and Technology (NUST), Islamabad, Pakistan
| | - Ishrat Jabeen
- Department of Sciences, School of Interdisciplinary Engineering and Sciences (SINES), National University of Sciences and Technology (NUST), Islamabad, Pakistan
| | - Yusra Sajid Kiani
- Department of Sciences, School of Interdisciplinary Engineering and Sciences (SINES), National University of Sciences and Technology (NUST), Islamabad, Pakistan
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Kovács ZM, Dienes C, Hézső T, Almássy J, Magyar J, Bányász T, Nánási PP, Horváth B, Szentandrássy N. Pharmacological Modulation and (Patho)Physiological Roles of TRPM4 Channel—Part 1: Modulation of TRPM4. Pharmaceuticals (Basel) 2022; 15:ph15010081. [PMID: 35056138 PMCID: PMC8781449 DOI: 10.3390/ph15010081] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Accepted: 01/06/2022] [Indexed: 02/06/2023] Open
Abstract
Transient receptor potential melastatin 4 is a unique member of the TRPM protein family and, similarly to TRPM5, is Ca2+-sensitive and permeable to monovalent but not divalent cations. It is widely expressed in many organs and is involved in several functions by regulating the membrane potential and Ca2+ homeostasis in both excitable and non-excitable cells. This part of the review discusses the pharmacological modulation of TRPM4 by listing, comparing, and describing both endogenous and exogenous activators and inhibitors of the ion channel. Moreover, other strategies used to study TRPM4 functions are listed and described. These strategies include siRNA-mediated silencing of TRPM4, dominant-negative TRPM4 variants, and anti-TRPM4 antibodies. TRPM4 is receiving more and more attention and is likely to be the topic of research in the future.
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Affiliation(s)
- Zsigmond Máté Kovács
- Department of Physiology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.M.K.); (C.D.); (T.H.); (J.A.); (J.M.); (T.B.); (P.P.N.); (B.H.)
- Doctoral School of Molecular Medicine, University of Debrecen, 4032 Debrecen, Hungary
| | - Csaba Dienes
- Department of Physiology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.M.K.); (C.D.); (T.H.); (J.A.); (J.M.); (T.B.); (P.P.N.); (B.H.)
- Doctoral School of Molecular Medicine, University of Debrecen, 4032 Debrecen, Hungary
| | - Tamás Hézső
- Department of Physiology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.M.K.); (C.D.); (T.H.); (J.A.); (J.M.); (T.B.); (P.P.N.); (B.H.)
- Doctoral School of Molecular Medicine, University of Debrecen, 4032 Debrecen, Hungary
| | - János Almássy
- Department of Physiology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.M.K.); (C.D.); (T.H.); (J.A.); (J.M.); (T.B.); (P.P.N.); (B.H.)
| | - János Magyar
- Department of Physiology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.M.K.); (C.D.); (T.H.); (J.A.); (J.M.); (T.B.); (P.P.N.); (B.H.)
- Division of Sport Physiology, Department of Physiology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary
| | - Tamás Bányász
- Department of Physiology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.M.K.); (C.D.); (T.H.); (J.A.); (J.M.); (T.B.); (P.P.N.); (B.H.)
| | - Péter P. Nánási
- Department of Physiology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.M.K.); (C.D.); (T.H.); (J.A.); (J.M.); (T.B.); (P.P.N.); (B.H.)
- Department of Dental Physiology and Pharmacology, Faculty of Dentistry, University of Debrecen, 4032 Debrecen, Hungary
| | - Balázs Horváth
- Department of Physiology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.M.K.); (C.D.); (T.H.); (J.A.); (J.M.); (T.B.); (P.P.N.); (B.H.)
- Faculty of Pharmacy, University of Debrecen, 4032 Debrecen, Hungary
| | - Norbert Szentandrássy
- Department of Physiology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary; (Z.M.K.); (C.D.); (T.H.); (J.A.); (J.M.); (T.B.); (P.P.N.); (B.H.)
- Department of Basic Medical Sciences, Faculty of Dentistry, University of Debrecen, 4032 Debrecen, Hungary
- Correspondence:
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Combined Pharmacophore and Grid-Independent Molecular Descriptors (GRIND) Analysis to Probe 3D Features of Inositol 1,4,5-Trisphosphate Receptor (IP 3R) Inhibitors in Cancer. Int J Mol Sci 2021; 22:ijms222312993. [PMID: 34884798 PMCID: PMC8657927 DOI: 10.3390/ijms222312993] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Revised: 11/18/2021] [Accepted: 11/24/2021] [Indexed: 12/11/2022] Open
Abstract
Inositol 1, 4, 5-trisphosphate receptor (IP3R)-mediated Ca2+ signaling plays a pivotal role in different cellular processes, including cell proliferation and cell death. Remodeling Ca2+ signals by targeting the downstream effectors is considered an important hallmark in cancer progression. Despite recent structural analyses, no binding hypothesis for antagonists within the IP3-binding core (IBC) has been proposed yet. Therefore, to elucidate the 3D structural features of IP3R modulators, we used combined pharmacoinformatic approaches, including ligand-based pharmacophore models and grid-independent molecular descriptor (GRIND)-based models. Our pharmacophore model illuminates the existence of two hydrogen-bond acceptors (2.62 Å and 4.79 Å) and two hydrogen-bond donors (5.56 Å and 7.68 Å), respectively, from a hydrophobic group within the chemical scaffold, which may enhance the liability (IC50) of a compound for IP3R inhibition. Moreover, our GRIND model (PLS: Q2 = 0.70 and R2 = 0.72) further strengthens the identified pharmacophore features of IP3R modulators by probing the presence of complementary hydrogen-bond donor and hydrogen-bond acceptor hotspots at a distance of 7.6-8.0 Å and 6.8-7.2 Å, respectively, from a hydrophobic hotspot at the virtual receptor site (VRS). The identified 3D structural features of IP3R modulators were used to screen (virtual screening) 735,735 compounds from the ChemBridge database, 265,242 compounds from the National Cancer Institute (NCI) database, and 885 natural compounds from the ZINC database. After the application of filters, four compounds from ChemBridge, one compound from ZINC, and three compounds from NCI were shortlisted as potential hits (antagonists) against IP3R. The identified hits could further assist in the design and optimization of lead structures for the targeting and remodeling of Ca2+ signals in cancer.
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Costa Pessoa J, Garribba E, Santos MF, Santos-Silva T. Vanadium and proteins: Uptake, transport, structure, activity and function. Coord Chem Rev 2015. [DOI: 10.1016/j.ccr.2015.03.016] [Citation(s) in RCA: 141] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Fraqueza G, Ohlin CA, Casey WH, Aureliano M. Sarcoplasmic reticulum calcium ATPase interactions with decaniobate, decavanadate, vanadate, tungstate and molybdate. J Inorg Biochem 2012; 107:82-9. [PMID: 22178669 DOI: 10.1016/j.jinorgbio.2011.10.010] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2011] [Revised: 10/08/2011] [Accepted: 10/20/2011] [Indexed: 02/07/2023]
Abstract
Over the last few decades there has been increasing interest in oxometalate and polyoxometalate applications to medicine and pharmacology. This interest arose, at least in part, due to the properties of these classes of compounds as anti-cancer, anti-diabetic agents, and also for treatment of neurodegenerative diseases, among others. However, our understanding of the mechanism of action would be improved if biological models could be used to clarify potential toxicological effects in main cellular processes. Sarcoplasmic reticulum (SR) vesicles, containing a large amount of Ca(2+)-ATPase, an enzyme that accumulates calcium by active transport using ATP, have been suggested as a useful model to study the effects of oxometalates on calcium homeostasis. In the present article, it is shown that decavanadate, decaniobate, vanadate, tungstate and molybdate, all inhibited SR Ca(2+)-ATPase, with the following IC(50) values: 15, 35, 50, 400 μM and 45 mM, respectively. Decaniobate (Nb(10)), is the strongest P-type enzyme inhibitor, after decavanadate (V(10)). Atomic-absorption spectroscopy (AAS) analysis, indicates that decavanadate binds to the protein with a 1:1 decavanadate:Ca(2+)-ATPase stoichiometry. Furthermore, V(10) binds with similar extension to all the protein conformations, which occur during calcium translocation by active transport, namely E1, E1P, E2 and E2P, as analysed by AAS. In contrast, it was confirmed that the binding of monomeric vanadate (H(2)VO(4)(2-); V(1)) to the calcium pump is favoured only for the E2 and E2P conformations of the ATPase, whereas no significant amount of vanadate is bound to the E1 and E1P conformations. Scatchard plot analysis, confirmed a 1:1 ratio for decavanadate-Ca(2+)-ATPase, with a dissociation constant, k(d) of 1 μM(-1). The interaction of decavanadate V(10)O(28)(6-) (V(10)) with Ca(2+)-ATPase is prevented by the isostructural and isoelectronic decaniobate Nb(10)O(28)(6-) (Nb(10)), whereas no significant effects were detected with ATP or with heparin, a known competitive ATP binding molecule, suggesting that V(10) binds non-competitively, with respect to ATP, to the protein. Finally, it was shown that decaniobate inhibits SR Ca(2+)-ATPase activity in a non competitive type of inhibition, with respect to ATP. Taken together, these data demonstrate that decameric niobate and vanadate species are stronger inhibitors of the SR calcium ATPase than simple monomeric vanadate, tungstate and molybdate oxometalates, thus affecting calcium homeostasis, cell signalling and cell bioenergetics, as well many other cellular processes. The ability of these oxometalates to act either as phosphate analogues, as a transition-state analogue in enzyme-catalysed phosphoryl group transfer processes and as potentially nucleotide-dependent enzymes modulators or inhibitors, suggests that different oxometalates may reveal different mechanistic preferences in these classes of enzymes.
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Affiliation(s)
- Gil Fraqueza
- Department of Food Engineering, ISE, University of Algarve, 8005-139 Faro, Portugal
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Aureliano M, Crans DC. Decavanadate (V10 O28 6-) and oxovanadates: oxometalates with many biological activities. J Inorg Biochem 2009; 103:536-46. [PMID: 19110314 DOI: 10.1016/j.jinorgbio.2008.11.010] [Citation(s) in RCA: 190] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2008] [Revised: 11/10/2008] [Accepted: 11/18/2008] [Indexed: 02/07/2023]
Abstract
The decameric vanadate species V(10)O(28)(6-), also referred to as decavanadate, impact proteins, lipid structures and cellular function, and show some effects in vivo on oxidative stress processes and other biological properties. The mode of action of decavanadate in many biochemical systems depends, at least in part, on the charge and size of the species and in some cases competes with the simpler oxovanadate species. The orange decavanadate that contains 10 vanadium atoms is a stable species for several days at neutral pH, but at higher pH immediately converts to the structurally and functionally distinct lower oxovanadates such as the monomer, dimer or tetramer. Although the biological effects of vanadium are generally assumed to derive from monomeric vanadate or the vanadyl cation, we show in this review that not all effects can be attributed to these simple oxovanadate forms. This topic has not previously been reviewed although background information is available [D.C. Crans, Comments Inorg. Chem. 16 (1994) 35-76; M. Aureliano (Ed.), Vanadium Biochemistry, Research Signpost Publs., Kerala, India, 2007]. In addition to pumps, channels and metabotropic receptors, lipid structures represent potential biological targets for decavanadate and some examples have been reported. Decavanadate interact with enzymes, polyphosphate, nucleotide and inositol 3-phosphate binding sites in the substrate domain or in an allosteric site, in a complex manner. In mitochondria, where vanadium was shown to accumulate following decavanadate in vivo administration, nM concentration of decavanadate induces membrane depolarization in addition to inhibiting oxygen consumption, suggesting that mitochondria may be potential targets for decameric toxicity. In vivo effects of decavanadate in piscine models demonstrated that antioxidant stress markers, lipid peroxidation and vanadium subcellular distribution is dependent upon whether or not the solutions administered contain decavanadate. The present review summarizes the reports on biological effects of decavanadate and highlights the importance of considering decavanadate in evaluations of the biological effects of vanadium.
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Affiliation(s)
- Manuel Aureliano
- CCMar and Dept. Chemistry, Biochemistry and Pharmacy, FCT, University of Algarve, Faro, Portugal.
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Michel AD, Xing M, Thompson KM, Jones CA, Humphrey PPA. Decavanadate, a P2X receptor antagonist, and its use to study ligand interactions with P2X7 receptors. Eur J Pharmacol 2006; 534:19-29. [PMID: 16487507 DOI: 10.1016/j.ejphar.2006.01.009] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2005] [Revised: 12/22/2005] [Accepted: 01/10/2006] [Indexed: 10/25/2022]
Abstract
In this study we have studied decavanadate effects at P2X receptors. Decavanadate competitively blocked 2'- and 3'-O-(4benzoylbenzoyl) ATP (BzATP) stimulated ethidium accumulation in HEK293 cells expressing human recombinant P2X7 receptors (pK(B) 7.5). The effects of decavanadate were rapid (minutes) in both onset and offset and contrasted with the much slower kinetics of pyridoxal 5-phosphate (P5P), Coomassie brilliant blue (CBB) and 1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine (KN62). Decavanadate competitively blocked the slowly reversible, or irreversible, blockade of the P2X7 receptor produced by P5P and oxidised ATP suggesting competition for a common binding site. However, the interaction between decavanadate and KN62 was non-competitive. Decavanadate also blocked P2X2 and P2X4 receptors but with slightly lower potency. These data demonstrate that decavanadate is the first reversible and competitive antagonist of the P2X7 receptor and is a useful tool for studying the mechanism of interaction of ligands with the P2X7 receptor.
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Affiliation(s)
- Anton D Michel
- Neurology and GI Centre of Excellence for Drug Discovery, GlaxoSmithKline Research and Development Limited, New Frontiers Science Park, Third Avenue, Harlow, Essex, CM19 5AW, UK.
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Wang D, Zhang W, Grüning K, Rehder D. Inorganic/organic hybrid salts derived from polyoxovanadates and macrocyclic (OxN2) cations. J Mol Struct 2003. [DOI: 10.1016/s0022-2860(03)00361-2] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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9
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Stojilkovic SS. Calcium Signaling Systems. Compr Physiol 1998. [DOI: 10.1002/cphy.cp070109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Farahbakhsh M, Schmidt H, Rehder D. A Decavandate Sandwiched by Diprotonated Cryptands-222: Model for the Vanadate-Ionophore Interaction. ACTA ACUST UNITED AC 1997. [DOI: 10.1002/cber.19971300814] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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del Pilar Gomez M, Nasi E. Activation of light-dependent K+ channels in ciliary invertebrate photoreceptors involves cGMP but not the IP3/Ca2+ cascade. Neuron 1995; 15:607-18. [PMID: 7546740 DOI: 10.1016/0896-6273(95)90149-3] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The activation of light-dependent K+ channels in ciliary photoreceptors from Pecten was investigated using intracellular dialysis of putative messengers and modulators. Neither elevated [Ca2+] nor BAPTA changed the membrane current in the dark or the light response. IP3 and the antagonists heparin and decavanadate were similarly ineffective, indicating that in these cells the IP3/Ca2+ signaling pathway is not crucial for phototransduction. By contrast, 8-Br-cGMP and cGMP induced an outward current accompanied by an increase in membrane conductance; 8-Br-cAMP was ineffective. The identity between the cGMP-induced and the light-induced currents is suggested by the following: both are carried by K+ and blocked by 4-AP, and both show outward rectification. In addition, guanine cyclic nucleotides depressed the photoresponse and induced single-channel currents in excised patches of light-sensitive membrane. These light-dependent channels therefore appear to represent a link between the families of cyclic nucleotide-gated channels and voltage-dependent K+ channels.
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Affiliation(s)
- M del Pilar Gomez
- Department of Physiology, Boston University School of Medicine, Massachusetts 02118, USA
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Mochizuki-Oda N, Nakajima Y, Nakanishi S, Ito S. Characterization of the substance P receptor-mediated calcium influx in cDNA transfected Chinese hamster ovary cells. A possible role of inositol 1,4,5-trisphosphate in calcium influx. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)36931-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Sandirasegarane L, Gopalakrishnan V. Limitations of the radioreceptor assay of inositol 1,4,5-trisphosphate in vanadate-treated cell suspensions. Biochem J 1994; 298 ( Pt 2):511-2. [PMID: 8135763 PMCID: PMC1137970 DOI: 10.1042/bj2980511] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
MESH Headings
- Animals
- Artifacts
- Cells, Cultured
- Inositol 1,4,5-Trisphosphate/analysis
- Male
- Muscle, Smooth, Vascular/chemistry
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/drug effects
- Radioligand Assay
- Rats
- Rats, Sprague-Dawley
- Vanadates/pharmacology
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Abstract
Bone cells can be exposed to high calcium in the course of endodontic treatment. To investigate the effects of high calcium on bone cell function, responses of a rat osteoblast cell line (UMR 106) were examined. Responsiveness of the cells to parathyroid hormone, prostaglandin F1 alpha, and ionomycin was assessed by measuring calcium transients elicited by these stimuli. Raising the medium calcium from 1.8 to 50 mM did not alter cell responsiveness. Pretreatment of the cells with the calcium pump inhibitor sodium vanadate prevented parathyroid hormone effects and slightly decreased prostaglandin F1 alpha effects in both normal and high calcium. The effect of ionomycin was prolonged in high calcium when vanadate was present. The results suggest that cells of the osteoblast phenotype can maintain calcium signaling in the presence of high extracellular calcium. These processes could play a role in the therapeutic effectiveness of high calcium in endodontic treatment.
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Affiliation(s)
- C S Haga
- Department of Graduate Endodontics, Northwestern University, Chicago, IL 60611
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Mochizuki-Oda N, Nakajima Y, Nakanishi S, Ito S. Substance P-induced elevation of intracellular calcium in transfected Chinese hamster ovary cells: role of inositol trisphosphate. REGULATORY PEPTIDES 1993; 46:450-2. [PMID: 7692564 DOI: 10.1016/0167-0115(93)90116-p] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Affiliation(s)
- N Mochizuki-Oda
- Department of Cell Biology, Osaka Bioscience Institute, Suita, Japan
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Föhr KJ, Warchol W, Gratzl M. Calculation and control of free divalent cations in solutions used for membrane fusion studies. Methods Enzymol 1993; 221:149-57. [PMID: 8361372 DOI: 10.1016/0076-6879(93)21014-y] [Citation(s) in RCA: 85] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- K J Föhr
- Naturwissenschuftliches und Medizinisches Institut, Universität Tübingen in Reutlingen, Germany
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Li W, Ye X, Tao L, Zhan Y, Cohen S, Yanoff M. Comparison and characterization of retinal pericytes and retinal pigment epithelial cells on subcellular IP3-sensitive Ca2+ pools. Cell Prolif 1992; 25:651-62. [PMID: 1457611 DOI: 10.1111/j.1365-2184.1992.tb01467.x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
A comparative study of inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ mobilization in bovine retinal capillary pericytes (BRCP) and bovine retinal pigment epithelial cells (BRPE) was carried out. Both cells were permeabilized with saponin. The two cell types had similar basal levels of [Ca2+]i (130 nM for BRCP, 132 nM for BRPE) and responded to IP3 in a dose-dependent manner. However, when stimulated by various concentrations of IP3 (1-10 microM), the increase in [Ca2+]i of BRCP was always two- to threefold higher than that in BRPE. Subcellular-fractionation studies showed that a single population of IP3 binding site with a high affinity and high specificity of IP3 mainly localized to plasma membrane in these two cell types. Although the dissociation constant of specific [32P]-IP3 binding sites (Kd 1.9-2.8 nM) was similar, the profile of maximal binding capacity (Bmax) of each fraction was markedly different. In comparison, plasma membrane fractions of BRCP were with Bmax of 165 fmol/mg protein versus 90 fmol/mg protein for BRPE membranes. The ATP-dependent Ca2+ uptake and IP3-dependent Ca2+ release were observed in the both plasma membrane fractions. With quantitative correlation, the membrane fraction (2 mg) of BRCP released 0.2 nmol Ca2+ whereas BRPE only released 0.07 nmol Ca2+ with the same dose of IP3 (5 microM). The selectively higher density of IP3 binding sites in coupling to the larger Ca(2+)-release in the membrane of BRCP suggests that the quantity of Ca2+ mobilized is determined by the spatially preferential distribution of membrane-associated IP3 binding sites. These findings may provide an explanation for the differences observed between BRCP and BRPE in IP3-induced DNA replication.
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Affiliation(s)
- W Li
- Department of Ophthalmology, Hahnemann University, Philadelphia, PA 19102
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Prolonged exposure to inositol 1,4,5-trisphosphate does not cause intrinsic desensitization of the intracellular Ca(2+)-mobilizing receptor. J Biol Chem 1992. [DOI: 10.1016/s0021-9258(18)42002-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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