Acidocalcisomes and a vacuolar H+-pyrophosphatase in malaria parasites

Plasmodium berghei trophozoites were loaded with the fluorescent calcium indicator, fura-2 acetoxymethyl ester, to measure their intracellular Ca2+ concentration ([Ca2+]i). [Ca2+]i was increased in the presence of the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibitor, thapsigargin. Trophozoites also possess a significant amount of Ca2+ stored in an acidic compartment. This was indicated by: (1) the increase in [Ca2+]i induced by bafilomycin A1, nigericin, monensin, or the weak base, NH4Cl, in the nominal absence of extracellular Ca2+, and (2) the effect of ionomycin, which cannot take Ca2+ out of acidic organelles and was more effective after alkalinization of this compartment by addition of bafilomycin A1, nigericin, monensin, or NH4Cl. Inorganic PPi promoted the acidification of a subcellular compartment in cell homogenates of trophozoites. The proton gradient driven by PPi collapsed by addition of the K+/H+ exchanger, nigericin, and eliminated by the PPi analogue, aminomethylenediphosphonate (AMDP). Both PPi hydrolysis and proton transport were dependent upon K+, and Na+ caused partial inhibition of these activities. PPi hydrolysis was sensitive in a dose-dependent manner to AMDP, imidodiphosphate, sodium fluoride, dicyclohexylcarbodi-imide and to the thiol reagent, N-ethylmaleimide. Immunofluorescence microscopy using antibodies raised against conserved peptide sequences of a plant vacuolar pyrophosphatase (V-H+-PPase) suggested that the proton pyrophosphatase is located in intracellular vacuoles and the plasma membrane of trophozoites. AMDP caused an increase in [Ca2+]i in the nominal absence of extracellular Ca2+. Ionomycin was more effective in releasing Ca2+ from this acidic intracellular compartment after treatment of the cells with AMDP. Taken together, these results suggest the presence in malaria parasites of acidocalcisomes with similar characteristics to those described in trypanosomatids and Toxoplasma gondii, and the colocalization of the V-H+-PPase and V-H+-ATPase in these organelles.

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Acidocalcisomes in Toxoplasma gondii tachyzoites

Biochemical Journal ◽

10.1042/bj3130655 ◽

1996 ◽

Vol 313 (2) ◽

pp. 655-659 ◽

Cited By ~ 106

Author(s):

Silvia N. J. MORENO ◽

Li ZHONG

Keyword(s):

Endoplasmic Reticulum ◽

Toxoplasma Gondii ◽

Mammalian Cells ◽

Specific Inhibitor ◽

Mitochondrial Atpase ◽

Bafilomycin A1 ◽

Atpase Inhibitor ◽

Extracellular Medium ◽

Acidic Compartment ◽

Acidic Organelles

Toxoplasma gondii tachyzoites were loaded with the fluorescent indicator fura 2 to investigate the transport mechanisms involved in maintaining their intracellular Ca2+ homoeostasis. The mitochondrial ATPase inhibitor oligomycin and the endoplasmic-reticulum Ca2+-ATPase inhibitor thapsigargin increased the intracellular Ca2+ concentration ([Ca2+]i), thus indicating the requirement for ATP and the involvement of the endoplasmic reticulum in maintaining intracellular Ca2+ homoeostasis. The effect of thapsigargin was more accentuated in the presence of extracellular Ca2+, clearly showing that, as occurs with other eukaryotic cells, depletion of intracellular Ca2+ pools led to an increase in the uptake of Ca2+ from the extracellular medium. In addition to these results, we found evidence that, in contrast with what occurs in mammalian cells, T. gondii tachyzoites possess a significant amount of Ca2+ stored in an acidic compartment, termed the acidocalcisome, as indicated by: (1) the increase in [Ca2+]i induced by bafilomycin A1 (a specific inhibitor of H+-ATPases), nigericin (a K+/H+ exchanger) or the weak base NH4Cl, in the nominal absence of extracellular Ca2+ to preclude Ca2+ entry; and (2) the effect of ionomycin, a Ca2+-releasing ionophore that cannot take Ca2+ out of acidic organelles and that was more effective after alkalinization of these compartments by addition of bafilomycin A1, nigericin or NH4Cl. Considering the relative importance of the ionomycin-releasable and the ionomycin+NH4Cl-releasable Ca2+ pools, it is apparent that T. gondii tachyzoites contain a significant amount of Ca2+ stored in acidocalcisomes.

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Ca2+ storage in Trypanosoma brucei: the influence of cytoplasmic pH and importance of vacuolar acidity

Biochemical Journal ◽

10.1042/bj3100789 ◽

1995 ◽

Vol 310 (3) ◽

pp. 789-794 ◽

Cited By ~ 32

Author(s):

D A Scott ◽

S N J Moreno ◽

R Docampo

Keyword(s):

Trypanosoma Brucei ◽

Ph Effect ◽

Calcium Ionophore ◽

Free Calcium ◽

Bafilomycin A1 ◽

Atpase Inhibitor ◽

Cytosolic Ph ◽

Permeabilized Cells ◽

Intracellular Compartments ◽

Acidic Compartment

The hypothesis that changes in cytosolic pH effect the release from intracellular compartments of stored calcium in Trypanosoma brucei was addressed by the use of procyclic and bloodstream trypomastigotes of T. brucei loaded with the fluorescent reagents 2′,7′-bis-(2-carboxyethyl)-5(and 6)-carboxyfluorescein (BCECF) to measure intracellular pH (pHi), or fura 2 to measure intracellular free calcium ([Ca2+]i). Experiments were performed in EGTA-containing buffers, so increases in [Ca2+]i reflected release of stored calcium rather than Ca2+ entry. Nigericin reduced pHi and increased [Ca2+]i in loaded cells, whilst propionate reduced pHi, but did not affect [Ca2+]i, and NH4Cl increased both variables, so there appears to be no correlation between pHi and [Ca2+]i. Treatment of the cells with the calcium ionophore ionomycin under similar conditions (nominal absence of extracellular Ca2+) resulted in an increase of [Ca2+]i which was greatly increased by addition of either NH4Cl, nigericin or the vacuolar H(+)-ATPase inhibitor bafilomycin A1. Similar results were obtained when the order of additions was reversed or when digitonin-permeabilized cells were used with the Ca2+ indicator arsenazo III. The results suggest that more Ca2+ is stored in this acidic compartment in procyclic than in bloodstream forms. Taking into account the relative importance of the ionomycin-releasable and the ionomycin-plus-NH4Cl-releasable Ca2+ pools, it is apparent that a significant amount of the Ca2+ stored in T. brucei trypomastigotes is present in the acidic compartment thus identified.

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Intracellular Ca2+ storage in acidocalcisomes of Trypanosoma cruzi

Biochemical Journal ◽

10.1042/bj3101005 ◽

1995 ◽

Vol 310 (3) ◽

pp. 1005-1012 ◽

Cited By ~ 137

Author(s):

R Docampo ◽

D A Scott ◽

A E Vercesi ◽

S N J Moreno

Keyword(s):

Trypanosoma Cruzi ◽

Acridine Orange ◽

Bafilomycin A1 ◽

Uptake Mechanism ◽

Acetoxymethyl Ester ◽

Permeabilized Cells ◽

Fura 2 ◽

Carbonyl Cyanide ◽

Acidic Compartment ◽

Proton Uptake

The use of digitonin to permeabilize the plasma membrane of Trypanosoma cruzi allowed the identification of a non-mitochondrial nigericin- or bafilomycin A1-sensitive Ca(2+)-uptake mechanism. Proton uptake, as detected by ATP-dependent Acridine Orange accumulation, was also demonstrated in these permeabilized cells. Under these conditions Acridine Orange was concentrated in abundant cytoplasmic round vacuoles. This latter process was inhibited (and reversed) by bafilomycin A1, nigericin and NH4Cl in different stages of T. cruzi. Ca2+ released Acridine Orange from permeabilized cells, suggesting that the dye and Ca2+ were being accumulated in the same acidic compartment and that Ca2+ was taken up in exchange for protons. Addition of bafilomycin A1 (5 microM), nigericin (1 microM) or carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP; 1 microM) to fura 2-loaded epimastigotes increased their intracellular Ca2+ concentration ([Ca2+]i). Although this effect was more noticeable in the presence of extracellular Ca2+, it was also observed in its absence. Addition of NH4Cl (10-40 mM) to different stages of T. cruzi, in the nominal absence of extracellular Ca2+ to preclude Ca2+ entry, increased both [Ca2+]i in fura 2-loaded cells, and intracellular pH (pHi) in 2′,7′-bis-(2-carboxyethyl)-5-(and -6)-carboxyfluorescein acetoxymethyl ester (BCECF)-loaded cells. Treatment of the cells with the Ca2+ ionophore ionomycin under similar conditions (nominal absence of extracellular Ca2+) resulted in an increase in [Ca2+]i and a significantly higher increase in [Ca2+]i after addition of NH4Cl, nigericin or bafilomycin A1, all agents which increase the pH of acidic compartments and make ionomycin more effective as a Ca(2+)-releasing ionophore. Similar results were obtained when the order of additions was reversed. Taking into account the relative importance of the ionomycin-releasable and the ionomycin plus NH4Cl-releasable Ca2+ pools, it is apparent that most of the Ca2+ stored in different stages of T. cruzi is present in the acidic compartment thus identified. Taken together, these results are consistent with the presence of a Ca2+/H+ exchange system in an acidic vacuole, which we have named the ‘acidocalcisome’ and which appears to be a unique organelle present in trypanosomatids.

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Vacuolar proton pyrophosphatase activity and pyrophosphate (PPi) in Toxoplasma gondii as possible chemotherapeutic targets

Biochemical Journal ◽

10.1042/bj3490737 ◽

2000 ◽

Vol 349 (3) ◽

pp. 737-745 ◽

Cited By ~ 47

Author(s):

Claudia O. RODRIGUES ◽

David A. SCOTT ◽

Brian N. BAILEY ◽

Wanderley DE SOUZA ◽

Marlene BENCHIMOL ◽

...

Keyword(s):

Toxoplasma Gondii ◽

Proton Transport ◽

Bone Diseases ◽

31P Nmr Spectroscopy ◽

Dependent Manner ◽

Subcellular Compartment ◽

Culture Cells ◽

Thiol Reagent ◽

Intracellular Proliferation ◽

Dose Dependent

The addition of PPi promoted the acidification of a subcellular compartment in cell homogenates of Toxoplasma gondii tachyzoites, implying the presence of a proton-translocating pyrophosphatase. The proton gradient was collapsed by addition of the K+/H+ antiporter nigericin, and was also inhibited by addition of the PPi analogue aminomethylenediphosphonate (AMDP). Both proton transport and PPi hydrolysis were dependent upon K+, but Na+ caused partial inhibition of these activities. PPi hydrolysis was sensitive in a dose-dependent manner to AMDP, imidodiphosphate, NaF and to the thiol reagent N-ethylmaleimide. This activity was unaffected by common inhibitors of phosphohydrolases, except that NaO3V (sodium orthovanadate) stimulated the activity by 87%. Immunofluorescence microscopy, using antisera raised against conserved peptide sequences of a plant vacuolar pyrophosphatase, suggested that the pyrophosphatase in T. gondii tachyzoites was located in the plasma membrane and intracellular vacuoles of the parasite. High-field 31P-NMR spectroscopy showed that PPi was more abundant than ATP in tachyzoites. Bisphosphonates (PPi analogues), drugs that are used in the treatment of bone diseases, inhibited proton transport and PPi hydrolysis in tachyzoite homogenates, and also inhibited intracellular proliferation of tachyzoites in tissue culture cells.

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The lysosomotrope GPN mobilises Ca2+from acidic organelles

Journal of Cell Science ◽

10.1242/jcs.256578 ◽

2021 ◽

Vol 134 (6) ◽

pp. jcs256578 ◽

Cited By ~ 1

Author(s):

Yu Yuan ◽

Bethan S. Kilpatrick ◽

Susanne Gerndt ◽

Franz Bracher ◽

Christian Grimm ◽

...

Keyword(s):

Acute Treatment ◽

Chronic Treatment ◽

The Novel ◽

Bafilomycin A1 ◽

Atpase Inhibitor ◽

Cytosolic Ph ◽

Lysosomal Ph ◽

Lysosomotropic Agent ◽

Acidic Organelles ◽

Primary Action

ABSTRACTLysosomes are acidic Ca2+stores often mobilised in conjunction with endoplasmic reticulum (ER) Ca2+stores. Glycyl-L-phenylalanine 2-naphthylamide (GPN) is a widely used lysosomotropic agent that evokes cytosolic Ca2+signals in many cells. However, whether these signals are the result of a primary action on lysosomes is unclear in light of recent evidence showing that GPN mediates direct ER Ca2+release through changes in cytosolic pH. Here, we show that GPN evoked rapid increases in cytosolic pH but slower Ca2+signals. NH4Cl evoked comparable changes in pH but failed to affect Ca2+. The V-type ATPase inhibitor, bafilomycin A1, increased lysosomal pH over a period of hours. Acute treatment modestly affected lysosomal pH and potentiated Ca2+signals evoked by GPN. In contrast, chronic treatment led to more profound changes in luminal pH and selectively inhibited GPN action. GPN blocked Ca2+responses evoked by the novel nicotinic acid adenine dinucleotide phosphate-like agonist, TPC2-A1-N. Therefore, GPN-evoked Ca2+signals were better correlated with associated pH changes in the lysosome compared to the cytosol, and were coupled to lysosomal Ca2+release. We conclude that Ca2+signals evoked by GPN most likely derive from acidic organelles.

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A new family of fluorescent calcium indicators designed to resist leakage or for measuring calcium near membranes

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100168578 ◽

1994 ◽

Vol 52 ◽

pp. 168-169

Author(s):

Martin Poenie ◽

Akwasi Minta ◽

Charles Vorndran

Keyword(s):

Metal Binding ◽

Acetoxymethyl Ester ◽

Binding Properties ◽

Fura 2 ◽

New Family ◽

Anion Transporter ◽

Calcium Indicator ◽

Calcium Indicators ◽

High Calcium ◽

Intracellular Compartmentalization

The use of fura-2 as an intracellular calcium indicator is complicated by problems of rapid dye leakage and intracellular compartmentalization which is due to a probenecid sensitive anion transporter. In addition there is increasing evidence for localized microdomains of high calcium signals which may not be faithfully reported by fura-2.We have developed a new family of fura-2 analogs aimed at addressing some of these problems. These new indicators are based on a modified bapta which can be readily derivatized to produce fura-2 analogs with a variety of new properties. The modifications do not affect the chromophore and have little impact on the spectral and metal binding properties of the indicator. One of these new derivatives known as FPE3 is a zwitterionic analog of fura-2 that can be loaded into cells as an acetoxymethyl ester and whose retention in cells is much improved. The improved retention of FPE3 is important for both cuvettebased measurements of cell suspensions and for calcium imaging.

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Vacuolar-type H+-ATPase regulates cytoplasmic pH in Toxoplasma gondii tachyzoites

Biochemical Journal ◽

10.1042/bj3300853 ◽

1998 ◽

Vol 330 (2) ◽

pp. 853-860 ◽

Cited By ~ 44

Author(s):

N. J. Silvia MORENO ◽

Li ZHONG ◽

Hong-Gang LU ◽

Wanderley DE SOUZA ◽

Marlene BENCHIMOL

Keyword(s):

Plasma Membrane ◽

Toxoplasma Gondii ◽

Laser Scanning ◽

Membrane Surface ◽

Surface Proteins ◽

Laser Scanning Microscopy ◽

Confocal Laser ◽

Dependent Manner ◽

Cytoplasmic Ph ◽

Bafilomycin A1

Cytoplasmic pH (pHi) regulation was studied in Toxoplasma gondii tachyzoites by using the fluorescent dye 2ʹ,7ʹ-bis-(2-carboxyethyl)-5(6)-carboxyfluorescein. Their mean baseline pHi (7.07±0.06; n = 5) was not significantly affected in the absence of extracellular Na+, K+ or HCO3- but was significantly decreased in a dose-dependent manner by low concentrations of N,Nʹ-dicyclohexylcarbodi-imide (DCCD), N-ethylmaleimide (NEM) or bafilomycin A1. Bafilomycin A1 also inhibited the recovery of tachyzoite pHi after an acid load with sodium propionate. Similar concentrations of DCCD, NEM and bafilomycin A1 produced depolarization of the plasma membrane potential as measured with bis-(1,3-diethylthiobarbituric)trimethineoxonol (bisoxonol), and DCCD prevented the hyperpolarization that accompanies acid extrusion after the addition of propionate, in agreement with the electrogenic nature of this pump. Confocal laser scanning microscopy indicated that, in addition to being located in cytoplasmic vacuoles, the vacuolar (V)-H+-ATPase of T. gondii tachyzoites is also located in the plasma membrane. Surface localization of the V-H+-ATPase was confirmed by experiments using biotinylation of cell surface proteins and immunoprecipitation with antibodies against V-H+-ATPases. Taken together, the results are consistent with the presence of a functional V-H+-ATPase in the plasma membrane of these intracellular parasites and with an important role of this enzyme in the regulation of pHi homoeostasis in these cells.

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Retrograde Transport from the Pre-Golgi Intermediate Compartment and the Golgi Complex Is Affected by the Vacuolar H+-ATPase Inhibitor Bafilomycin A1

Molecular Biology of the Cell ◽

10.1091/mbc.9.12.3561 ◽

1998 ◽

Vol 9 (12) ◽

pp. 3561-3578 ◽

Cited By ~ 66

Author(s):

Harri Palokangas ◽

Ming Ying ◽

Kalervo Väänänen ◽

Jaakko Saraste

Keyword(s):

Brefeldin A ◽

Retrograde Transport ◽

Small Gtpase ◽

Bafilomycin A1 ◽

Atpase Inhibitor ◽

Marker Proteins ◽

Golgi Region ◽

Intermediate Compartment ◽

Acidic Compartments

The effect of the vacuolar H+-ATPase inhibitor bafilomycin A1 (Baf A1) on the localization of pre-Golgi intermediate compartment (IC) and Golgi marker proteins was used to study the role of acidification in the function of early secretory compartments. Baf A1 inhibited both brefeldin A- and nocodazole-induced retrograde transport of Golgi proteins to the endoplasmic reticulum (ER), whereas anterograde ER-to-Golgi transport remained largely unaffected. Furthermore, p58/ERGIC-53, which normally cycles between the ER, IC, and cis-Golgi, was arrested in pre-Golgi tubules and vacuoles, and the number of p58-positive ∼80-nm Golgi (coatomer protein I) vesicles was reduced, suggesting that the drug inhibits the retrieval of the protein from post-ER compartments. In parallel, redistribution of β-coatomer protein from the Golgi to peripheral pre-Golgi structures took place. The small GTPase rab1p was detected in short pre-Golgi tubules in control cells and was efficiently recruited to the tubules accumulating in the presence of Baf A1. In contrast, these tubules showed no enrichment of newly synthesized, anterogradely transported proteins, indicating that they participate in retrograde transport. These results suggest that the pre-Golgi structures contain an active H+-ATPase that regulates retrograde transport at the ER–Golgi boundary. Interestingly, although Baf A1 had distinct effects on peripheral pre-Golgi structures, only more central, p58-containing elements accumulated detectable amounts of 3-(2,4-dinitroanilino)-3′-amino-N-methyldipropylamine (DAMP), a marker for acidic compartments, raising the possibility that the lumenal pH of the pre-Golgi structures gradually changes in parallel with their translocation to the Golgi region.

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Effects of bafilomycin A1 on cytosolic pH of sheep alveolar and peritoneal macrophages: evaluation of the pH-regulatory role of plasma membrane V-ATPases.

Journal of Experimental Biology ◽

10.1242/jeb.198.8.1711 ◽

1995 ◽

Vol 198 (8) ◽

pp. 1711-1715 ◽

Cited By ~ 1

Author(s):

T A Heming ◽

D L Traber ◽

F Hinder ◽

A Bidani

Keyword(s):

Plasma Membrane ◽

Atpase Activity ◽

Initial Rate ◽

Cell Types ◽

Peritoneal Macrophages ◽

Bafilomycin A1 ◽

Atpase Inhibitor ◽

Cytosolic Ph ◽

Phi Regulation

The role of plasma membrane V-ATPase activity in the regulation of cytosolic pH (pHi) was determined for resident alveolar and peritoneal macrophages (m theta) from sheep. Cytosolic pH was measured using 2',7'-biscarboxyethyl-5,6-carboxyfluorescein (BCECF). The baseline pHi of both cell types was sensitive to the specific V-ATPase inhibitor bafilomycin A1. Bafilomycin A1 caused a significant (approximately 0.2 pH units) and rapid (within seconds) decline in baseline pHi. Further, bafilomycin A1 slowed the initial rate of pHi recovery (dpHi/dt) from intracellular acid loads. Amiloride had no effects on baseline pHi, but reduced dpHi/dt (acid-loaded pHi nadir < 6.8) by approximately 35%. Recovery of pHi was abolished by co-treatment of m theta with bafilomycin A1 and amiloride. These data indicate that plasma membrane V-ATPase activity is a major determinant of pHi regulation in resident alveolar and peritoneal m theta from sheep. Sheep m theta also appear to possess a Na+/H+ exchanger. However, Na+/H+ exchange either is inactive or can be effectively masked by V-ATPase-mediated H+ extrusion at physiological pHi values.

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Properties of neuroprotective cell-permeant Ca2+ chelators: effects on [Ca2+]i and glutamate neurotoxicity in vitro

Journal of Neurophysiology ◽

10.1152/jn.1994.72.4.1973 ◽

1994 ◽

Vol 72 (4) ◽

pp. 1973-1992 ◽

Cited By ~ 66

Author(s):

M. Tymianski ◽

M. P. Charlton ◽

P. L. Carlen ◽

C. H. Tator

Keyword(s):

Time Course ◽

Dependent Manner ◽

Protective Effects ◽

Tetraacetic Acid ◽

Acetoxymethyl Ester ◽

Neuroprotective Effects ◽

Concentration Dependent Manner ◽

Fura 2 ◽

Glutamate Neurotoxicity

1. Cell-permeant Ca2+ chelators such as 1,2-bis-(2-amino-phenoxy)ethane- N,N,N',N'-tetraacetic acid acetoxymethyl ester (BAPTA-AM) protect neurons against excitotoxic and ischemic neuronal injury in vitro and in vivo. Here we provide the first steps toward characterizing the mechanisms by which these agents produce their neuroprotective effects. 2. Cultured mouse spinal neurons were simultaneously loaded with the Ca2+ indicator fura-2 and with one of three permeant chelators derived from the fast Ca2+ buffer BAPTA, or with ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid acetoxymethyl ester (EGTA-AM). Adding these chelators did not interfere with the fluorescence spectrum of fura-2 and had no effect on baseline [Ca2+]i. 3. The neurons were challenged with 250 microM L-glutamate for 50 min, producing a marked transient [Ca2+]i increase followed by a decay of [Ca2+]i to a lower “plateau.” About 80% of control neurons succumbed to this excitotoxic insult. Neurons that survived adjusted their plateau [Ca2+]i to lower levels than those that succumbed. 4. Neurons that were pretreated with permeant Ca2+ chelators became more resistant to these neurotoxic challenges. 5. We examined whether this reduction in glutamate neurotoxicity could be related to the given buffer's known Ca2+ affinity (Kd), its Ca2+ binding kinetics, and its ability to attenuate glutamate-induced [Ca2+]i increases. 6. Pretreatment of neurons with BAPTA analogues having Kds ranging from 100 to 3,600 microM 1) attenuated the amplitude and 2) lengthened the time constant describing the rise and decay of the glutamate-evoked [Ca2+]i transient. The magnitude of these effects paralleled the affinity of the chelator for Ca2+. 7. BAPTA-AM and its analogues dramatically attenuated the early neurotoxicity of glutamate, reducing cell deaths by up to 80%. However, in contrast with the graded effects of chelators having different Ca2+ affinities on Ca2+ transients, all BAPTA analogues were equally protective. These protective effects did not relate to the chelators' Ca2+ affinity within a Kd range of 100 nM (for BAPTA) to 3,600 nM (for 5,5'-dibromo BAPTA). 8. BAPTA-AM protected neurons in a concentration-dependent manner with 50% protection obtained with 10 microM, a concentration having no effect on the [Ca2+]i transient amplitude. 9. EGTA, a slow Ca2+ buffer with a similar Ca2+ affinity to BAPTA produced the same effects as BAPTA on [Ca2+]i transient kinetics. However, it was far less protective than BAPTA. 10. The time course of early glutamate neurotoxicity was altered by the BAPTA analogues, but not EGTA. BAPTA analogues caused a small increase in cell deaths in the first minutes of each experiment, followed by relative sparing from further neurodegeneration. 11. The ability of low Ca2+ affinity chelators such as 5,5'-dibromo BAPTA to protect neurons without markedly attenuating measured [Ca2+]i increases conflicts with the hypothesis that global elevations in [Ca2+]i are responsible for triggering neurotoxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

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