Does ionophore A23187 mediate Na transport in the absence of divalent cations?

Nature ◽  
1977 ◽  
Vol 270 (5636) ◽  
pp. 444-445 ◽  
Author(s):  
PETER FLATMAN ◽  
VIRGILIO L. LEW
Keyword(s):  
Divalent Cations ◽  
Ionophore A23187 ◽  
Na Transport

scholarly journals The role of divalent cations in the regulation of microtubule assembly. In vivo studies on microtubules of the heliozoan axopodium using the ionophore A23187.

1976 ◽  
Vol 70 (3) ◽  
pp. 527-540 ◽  
Author(s):  
M Schliwa
Keyword(s):  
Divalent Cations ◽  
Light And Electron Microscopy ◽  
Microtubule Assembly ◽  
In Vivo Studies ◽  
Ionophore A23187 ◽  
Low Concentrations ◽  
Microtubule Formation

Low concentrations of calcium and magnesium ions have been shown to influence microtubule assembly in vitro. To test whether these cations also have an effect on microtubules in vivo, specimens of Actinosphaerium eichhorni were exposed to different concentrations of Ca++ and Mg++ and the divalent cation ionophore A23187. Experimental degradation and reformation of axopodia were studied by light and electron microscopy. In the presence of Ca++ and the ionophore axopodia gradually shorten, the rate of shortening depending on the concentrations of Ca++ and the ionophore used. Retraction of axopodia was observed with a concentration of Ca++ as low as 0.01 mM. After transfer to a Ca++-free solution containing EGTA, axopodia re-extend; the initial length is reached after about 2 h. Likewise, reformation of axopodia of cold-treated organisms is observed only in solutions of EGTA or Mg++, whereas it is completely inhibited in a Ca++ solution. Electron microscope studies demonstrate degradation of the axonemal microtubular array in organisms treated with Ca++ and A23187. No alteration was observed in organisms treated with Mg++ or EGTA plus ionophore. The results suggest that, in the presence of the ionophore, formation of axonemal microtubules can be regulated by varying the Ca++ concentration in the medium. Since A23187 tends to equilibrate the concentrations of divalent cations between external medium and cell interior, it is likely that microtubule formation invivo is influenced by micromolar concentrations of Ca++. These concentrations are low enough to be of physiological significance for a role in the regulation of microtubule assembly in vivo.

Calcium Ionophore A23187 (Eli Lilly)

1975 ◽  
Vol 34 (01) ◽  
pp. 072-082 ◽  
Author(s):  
Erik H Mürer ◽  
Gwendolyn J Stewart ◽  
Michael A Rausch ◽  
H. James Day
Keyword(s):  
Divalent Cations ◽  
Adenine Nucleotides ◽  
Cell Metabolism ◽  
Calcium Ionophore ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Extracellular Medium ◽  
Inosine Monophosphate ◽  
Cytoplasmic Material ◽  
Physiologic Effect

SummaryThe addition of 0.1 μM ionophore A23187 to washed platelets incubated in citrated saline caused massive release of stored serotonin accompanied by intracellular accumulation of inosine monophosphate, but produced no detectable influx of externally added calcium or abnormal structural alterations. With increasing ionophore concentration there was a significant influx of calcium and a drastic alteration in the platelet ultrastructure. The increase in ionophore concentration was accompanied by the conversion of the major part of metabolic adenine nucleotides to inosine monophosphate and an almost complete blockage of further conversion to inosine and hypoxanthine. The metabolic changes were accentuated by the addition of calcium at concentrations less than 1/10 of the citrate concentration. In the presence of Ca++, or when citrate was omitted, there was a substantial leakage of cytoplasmic material, which at times suggested complete exchangeability between cytoplasm and extracellular medium. Our findings are consistent with the hypothesis that the platelet release reaction is triggered by intracellularly bound calcium. They also suggest that the application of high ionophore concentration has a toxicologic rather than a physiologic effect on platelets, and that a weak chelator added during incubation with the ionophore can in the absence of divalent cations prevent cell destruction, but not the toxic effect on cell metabolism.

scholarly journals Inhibition of K transport by divalent cations in sickle erythrocytes

Blood ◽  
1987 ◽  
Vol 70 (6) ◽  
pp. 1810-1815 ◽  
Author(s):  
C Brugnara ◽  
DC Tosteson
Keyword(s):  
Volume Regulation ◽  
Divalent Cations ◽  
Cell Swelling ◽  
Ionophore A23187 ◽  
Divalent Ions ◽  
Normal Cells ◽  
A Value ◽  
Sickle Erythrocytes ◽  
Mg Content ◽  
K Transport

Abstract We report experiments on the effect of intracellular divalent cations (Mg, Ca, Mn) on K transport and cell volume in erythrocytes from patients with homozygous hemoglobin S disease (SS cells). When CO- treated SS erythrocytes are exposed to the ionophore A23187, removal of cell Mg markedly stimulates K efflux, whereas increasing cell Mg inhibits K efflux. The Ki for the inhibition by internal free Mg is 0.38 +/- 0.10 mmol/L, a value comparable to the concentration of free Mg in normal cells (0.3 to 0.4 mmol/L). When swollen SS cells with increased Mg content were incubated in plasma-like medium, they shrunk much less than swollen SS cells with normal Mg content. Thus, elevation of cell Mg produces inhibition of swelling-induced K movement from SS cells. Internal Ca and Mn also inhibit K movement from SS cells. The inhibition of volume regulation by divalent cations suggests that increases in intracellular divalent ions, especially Mg, could induce a persistent degree of cell swelling in SS RBCs and thereby inhibit intracellular polymerization.

Ca-sensitive Na transport in sheep omasum

1999 ◽  
Vol 276 (6) ◽  
pp. G1331-G1344 ◽  
Author(s):  
Gerhard Schultheiss ◽  
Holger Martens
Keyword(s):  
Divalent Cations ◽  
Short Circuit ◽  
Short Circuit Current ◽  
Voltage Divider ◽  
Close Correlation ◽  
Na Transport ◽  
Luminal Side ◽  
Flux Measurements ◽  
Voltage Divider Ratio ◽  
Peak Value

Na transport across a preparation of sheep omasum was studied. All tissues exhibited a serosa-positive short-circuit current ( I sc), with a range of 1–4 μeq ⋅ h−1 ⋅ cm−2. A Michaelis-Menten-type kinetic was found between the Na concentration and the I sc(Michaelis-Menten constant for transport of Na = 6.7 mM; maximal transport capacity of Na = 4.16 μeq ⋅ h−1 ⋅ cm−2). Mucosal amiloride (1 mM), phenamil (1 or 10 μ), or serosal aldosterone (1 μM for 6 h) did not change I sc. Removal of divalent cations (Ca and Mg) enhanced I sc considerably from 2.61 ± 0.24 to a peak value of 11.18 ± 1.1 μeq ⋅ h−1 ⋅ cm−2. The peak I sc(overshoot) immediately declined to a plateau I sc of ∼6–7 μeq ⋅ h−1 ⋅ cm−2. Na flux measurements showed a close correlation between changes in I sc and Na transport. Transepithelial studies demonstrated that K, Cs, Rb, and Li are transported, indicating putative nonselective cation channels, which are inhibited by divalent cations (including Ca, Mg, Sr, Ba) and by (trivalent) La. Intracellular microelectrode recordings from the luminal side clearly showed changes of voltage divider ratio when mucosal divalent cations were removed. The obtained data support the assumption of a distinct electrogenic Na transport mechanism in sheep omasum.

scholarly journals Gap junction dynamics: reversible effects of divalent cations.

1980 ◽  
Vol 87 (3) ◽  
pp. 708-718 ◽  
Author(s):  
C Peracchia ◽  
L L Peracchia
Keyword(s):  
Gap Junction ◽  
Divalent Cations ◽  
Ionophore A23187 ◽  
Channel Narrowing ◽  
Lens Fibers ◽  
Electrical Uncoupling ◽  
Cytoplasmic Surface ◽  
Particle Packings ◽  
Cytoskeletal Elements ◽  
Junction Structure

Reversible changes in gap junction structure similar to those previously seen to parallel electrical uncoupling (9, 33, 34) are produced by treating with Ca++ or Mg++ gap junctions isolated in EDTA from calf lens fibers. The changes, characterized primarily by a switch from disordered to crystalline particle packings, occur at a [Ca++] of 5 x 10(-7) M or higher and a [Mg++] of 1 x 10(-3) M or higher and can be reversed by exposing the junctions to Ca++- and Mg++-free EGTA solutions. Similar changes are obtained in junctions of rat stomach epithelia incubated at 37 degrees C in well-oxygenated Tyrode's solutions containing a Ca++ ionophore (A23187). Deep etching experiments on isolated lens junctions show that the true cytoplasmic surface of the junctions (PS face) is mostly bare, suggesting that the particles may not be connected to cytoskeletal elements. A hypothesis is proposed suggesting a mechanism of particle aggregation and channel narrowing based on neutralization of negative charges by divalent cations or H+.

scholarly journals Intermittent swimming in live sea urchin sperm.

1980 ◽  
Vol 84 (1) ◽  
pp. 1-12 ◽  
Author(s):  
B H Gibbons
Keyword(s):  
Sea Urchin ◽  
Divalent Cations ◽  
Dark Field ◽  
Proximal Region ◽  
Ionophore A23187 ◽  
Quiescent State ◽  
Sodium Barbital ◽  
Dark Field Microscopy ◽  
Short Period ◽  
Live Sperm

Sperm of the sea urchin Tripneustes gratilla repeatedly start and stop swimming when suspended in seawater and observed by dark-field microscopy. While in the quiescent state, which usually lasts about a second, the sperm assume s shape resembling a cane, with a sharp bend of approximately 3.4 rad in the proximal region of the flagellum and very little curvature in the rest of the flagellum except for a slight curve near the tip. The occurrence of quiescence requires the presence of at least 2 mM Ca2+ in the seawater, and the percentage of sperm quiescent at any one time increases substantially when the sperm are illuminated with blue light. With intense illumination, close to 100% of the sperm become quiescent, and this percentage decreases gradually to approximately 0.3% over a 10(4)-fold decrease in light intensity. An increased concentration of K+ in the seawater also increases the percentage of quiescence, with a majority of the sperm being quiescent in seawater containing 80 mM KCl. The induction of quiescence by light or by increased KCl is completely inhibited by 10 micrometers chlorpromazine, and approximately 90% inhibited by 1 mM procaine or sodium barbital. Sperm treated with the divalent-cation ionophore A23187 swim quite normally, although for a relatively short period, in artificial seawater lacking divalent cations, but are abruptly arrested upon addition of 0.04--0.2 mM free Ca2%. The flagellar waveform of these arrested sperm is almost identical to that of light-induced quiescence in the live sperm. The results support the hypothesis that quiescence is induced by a rise in intracellular Ca2%, perhaps as a consequence of a membrane depolarization, and that it is similar to the arrest response in cilia.

scholarly journals Regulation of macrophage lysosomal enzyme secretion: role of arachidonate metabolites, divalent cations and cyclic AMP

1980 ◽  
Vol 44 (1) ◽  
pp. 299-315
Author(s):  
R.M. McMillan ◽  
D.E. Macintyre ◽  
J.E. Beesley ◽  
J.L. Gordon
Keyword(s):  
Cyclic Amp ◽  
Lysosomal Enzyme ◽  
Lysosomal Enzymes ◽  
Divalent Cations ◽  
Cell Types ◽  
Enzyme Secretion ◽  
Ionophore A23187 ◽  
Enzyme Release ◽  
Arachidonate Metabolites

We have investigated the role in macrophage lysosomal enzyme release of arachidonate metabolites, extracellular divalent cations and cyclic AMP (cAMP) which modulate secretion in other cell types. Lysosomal enzyme secretion induced by zymosan was accompanied by release of malondialdehyde (MDA), which is derived from arachidonic acid via prostaglandin synthase. Blockade of MDA formation, by aspirin or indomethacin, was associated with only a small inhibitory effect on lysosomal enzyme release by zymosan: arachidonate metabolites thus play only a minor role in mediating macrophage lysosomal enzyme release. Zymosan-induced secretion of lysosomal enzymes from macrophages did not require extracellular magnesium or calcium although release was enhanced by magnesium and inhibited by calcium. These effects may be related to an influence of the ions on phagocytosis. Elevation of intracellular divalent cation concentrations, by ionophore A23187, induced release of lysosomal enzymes but this was a result of cell lysis. Adenylate cyclase stimulants and dibutyryl cAMP produced slight inhibition of zymosan-induced lysosomal enzyme release. Aminophylline and papaverine caused more marked inhibition but their effects may be due to actions independent of phosphodiesterase inhibition. Our data indicate that arachidonate metabolites and cAMP do not play a major role in regulating zymosan-induced enzyme release from macrophages. Extracellular calcium and magnesium may modulate secretion but the role of intracellular divalent cations remains to be established. We conclude that macrophage lysosomal enzyme secretion is controlled by regulatory mechanisms different from those which control similar degranulation processes in other cell types.

scholarly journals Role of calcium ions in the control of embryogenesis of Xenopus. Changes in the subcellular distribution of calcium in early cleavage embryos after treatment with the ionophore A23187.

1979 ◽  
Vol 80 (3) ◽  
pp. 589-604 ◽  
Author(s):  
J C Osborn ◽  
C J Duncan ◽  
J L Smith
Keyword(s):  
Divalent Cations ◽  
Subsequent Development ◽  
Abnormal Development ◽  
Ionophore A23187 ◽  
Early Cleavage ◽  
Amphibian Embryo ◽  
High Incidence ◽  
Intracellular Action

Treatment of stage 5 Xenopus embryos with the ionophore A23187 for only 10 min, in the absence of extracellular Mg2+ and Ca2+, causes cortical contractions and a high incidence of abnormal embryos during subsequent development. Cation analysis shows that divalent ions are not lost from the embryos, but that Ca2+ is redistributed within the subcellular fractions. Ca2+ is probably released from yolk platelets and/or pigment granules by the action of A23187, [Ca2+] rises in the cytosol, and the mitochondria attempt to take up this free Ca2+. The mitochondria concomitantly undergo characteristic ultrastructural transformations, changing towards energized-twisted and energized-zigzag conformations. A23187 allows these changes to be demonstrated in situ. Extracellular divalent cations (10(-4) M) interfere with this intracellular action of A23187. Intracellular accumulation of Na+ (by treatment with ouabain) or Li+ also causes abnormal development, probably by promoting a release of Ca2+ from the mitochondria. It is suggested (a) that all these treatments cause a rise in [Ca2+]i which interferes with normal, integrated cell division, so causing, in turn, abnormal embryogenesis, (b) that levels of [Ca2+]i are of importance in regulating cleavage, (c) that the mitochondria could well have a function in regulating [Ca2+]i during embryogenesis in Xenopus, and (d) that vegetalizing agents may well act by promoting a rise in [Ca2+]i in specific cells in the amphibian embryo.

Equilibria between ionophore A23187 and divalent cations: stability of 1:1 complexes in solutions of 80% methanol/water

Biochemistry ◽  
1987 ◽  
Vol 26 (16) ◽  
pp. 5009-5018 ◽  
Author(s):  
Clifford J. Chapman ◽  
Anil K. Puri ◽  
Richard W. Taylor ◽  
Douglas R. Pfeiffer
Keyword(s):  
Divalent Cations ◽  
Ionophore A23187
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