Physical properties of biological membranes determined by the fluorescence of the calcium ionophore A23187

Case, George D.; Vanderkooi, Jane M.; Scarpa, Antonio

doi:10.1016/0003-9861(74)90116-7

Cited by 111 publications

(36 citation statements)

References 33 publications

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“…It has recently been established that one of the earliest steps occurring at the acinar cell membrane in response to stimulation by ACh and pancreozymin is an increase in the permeability to Na+ with a consequent depolarization (Matthews & Petersen, 1973;Nishiyama & Petersen, 1974;Nishiyama & Petersen, 1975 (Pressman, 1973;Case, Vanderkooi & Scarpa, 1974). Also the failure of A23187 to evoke any marked depolarization at a Mg2+ concentration of 10 mm in the absence of Ca2+ makes the simple interpretation unlikely, since it is known that the ionophore complexes Mg2+ equally well as Ca2+ (Reed & Lardy, 1972).…”

Section: Discussionmentioning

confidence: 99%

Effects of the calcium ionophore A23187 on pancreatic acinar cell membrane potentials and amylase release.

Poulsen¹,

Williams²

1977

The Journal of Physiology

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SUMMARY1. The effects of the Ca2+-ionophore A23187 and the non-metabolizable cholinergic agonist bethanechol on acinar cell membrane potentials and amylase release from the superfused mouse pancreas were studied.2. In the presence of extracellular Ca2+ (2.56 mM), A23187 (10-5M) and bethanechol (3 x 10-, M) caused an equal increase in the release of amylase. Both stimulants depolarized the acinar cells, A23187 by 60 mV and bethanechol by 12-3 mV.3. When Ca2+ and Mg2+ were removed from the superfusate, the ability of A23187 to increase the rate of amylase release was virtually abolished, while the effect of bethanechol remained unaltered. Similarly, in the absence of these divalent cations, A23187 did not cause depolarization of the acinar cells, while depolarization in response to bethanechol was largely normal. Consequently it is unlikely that cholinergic agonists initiate secretion by activating a Ca2+-ionophore-like mechanism in the cell membrane.4. When the concentration of Ca2+ in the medium was raised to 10 mM, as the only divalent cation present, the depolarization in response to A23187 was increased to 11-8 mV. When Mg2+ in a concentration of 10 mM was the only extracellular divalent cation, the depolarization was only 2-1 mV.5. The Ca2+ dependent, A23187-induced depolarization was abolished in the absence of Na+ (Tris substitution). Addition of Na+ to the superfusate caused an immediate depolarization.6. It is concluded that the Ca2+ dependent depolarization of pancreatic acinar cells induced by A23187 is not directly due to an increased divalent

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Section: Discussionmentioning

confidence: 99%

Effects of the calcium ionophore A23187 on pancreatic acinar cell membrane potentials and amylase release.

Poulsen¹,

Williams²

1977

The Journal of Physiology

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“…However, because both ionophores have been shown to transport monovalent cations as well, it is possible that the effect observed is due to the movement of ions other than calcium (7,(29)(30)(31)(32)(33). Further studies will be required to investigate this possibility.…”

Section: Introductionmentioning

confidence: 99%

Bone resorption in organ culture: inhibition by the divalent cation ionophores A23187 and X-537A.

Ivey¹,

Wright²,

Tashjian³

1976

J. Clin. Invest.

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The ionophores A23187 and X-537A were used as probes to investigate the possible role of calcium uptake by bone as a mediator for the stimulation of bone resorption induced by parathyroid hormone (PTH) and other agents in cultured mouse calvaria. The ionophores alone at concentrations from 1 nM to 20 ,uM did not stimulate bone resorption, nor did they potentiate bone resorption stimulated by submaximal concentrations of PTH after either brief (15-60 min) or extended (1-3 day) exposure to the ionophores. Unexpectedly, we found that the ionophores inhibit in a dose-dependent manner bone resorption stimulated by PTH and a wide variety of other compounds (prostaglandin E2, la-hydroxycholecalciferol, 3-isobutyl-l-methylxanthine, and phorbol myristate acetate). This inhibition was not due to irreversible damage to the bones by the ionophores, because the inhibition was reversible even after 24 h of treatment. Inhibition of bone resorption by the ionophores was observed in media of both high and low calcium concentration, indicating that the inhibition was not due to a critical extracellular calcium concentration. Inhibition by the ionophores differs qualitatively in several ways from that produced by calcitonin, a natural inhibitor of bone resorption. Furthermore, A23187 at 1.0 ,ug/ml had no effect on the accumulation of cyclic AMP in the medium of either control, PTH-or calcitonintreated calvaria. We conclude that the ionophores A23187 or X-537A do not stimulate bone resorption

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“…This substance promotes transmembrane transport of divalent cations with a high affinity for Ca ++ and Mg ++ (28,34). Recently, A23187 has repeatedly been used in the study of Ca++-dependent cellular activities (e.g., references 4,9,19,22,43,46).…”

mentioning

confidence: 99%

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

Schliwa¹

1976

The Journal of Cell Biology

103

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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 in vivo 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.Many functions with which microtubules are associated depend on their ordered assembly and disassembly. In vivo studies clearly show that formation and breakdown of microtubules are influenced by temperature, hydrostatic pressure, and D20 (for review, see reference 48). These

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Physical properties of biological membranes determined by the fluorescence of the calcium ionophore A23187

Cited by 111 publications

References 33 publications

Effects of the calcium ionophore A23187 on pancreatic acinar cell membrane potentials and amylase release.

Effects of the calcium ionophore A23187 on pancreatic acinar cell membrane potentials and amylase release.

Bone resorption in organ culture: inhibition by the divalent cation ionophores A23187 and X-537A.

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

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