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Membrane Transport
Published in Lelio G. Colombetti, Biological Transport of Radiotracers, 2020
These ionophores have also been shown to exchange ions in biological systems. In red cells, the use of ionophores indicated that Cl- transport occurs according to a “silent” mechanism (see below). K+ release from red cells is measured (see Figure 10). Adding valinomycin did not significantly speed up K+ flux, because there was no net Cl- efflux to provide electroneutrality. Adding the proton carrier FCCP did enhance K+ efflux because K+ could be exchanged for protons. Adding nigericin instead did the same as the combination of valinomycin and FCCP because nigericin by itself can act as a K+–H+ exchange carrier.
Membrane Properties of Peritoneal Macrophage
Published in Richard C. Niemtzow, Transmembrane Potentials and Characteristics of Immune and Tumor Cell, 2020
The potential importance of an increase in membrane permeability to Ca+ + and an increase in intracellular Ca++ in initiating the events which lead to activation of macrophage is demonstrated by two observations. Specifically, the artificial increase of Ca+ + permeability by the application of the calcium ionophore, A23187, alters the electrical properties of nonactivated macrophage to resemble those of activated ones. In Figure 6, the current-voltage relationships of several macrophage are depicted. One plot shows the current-voltage relationship obtained from a typical cell obtained from a sample of activated cells, while the other plots show the I-V relationship for a nonactivated cell and the same cell after addition of 10 6M calcium ionophore. The ionophore causes an alteration of the relationship in a manner suggestive of activation.
Prostaglandins and the Mechanism of Bone Resorption
Published in Wilson Harvey, Alan Bennett, Prostaglandins in Bone Resorption, 2020
Unfortunately the use of calcium ionophores and antagonists has produced some conflicting results. Ivey et al.44 found that two ionophores inhibited resorption induced by PGE2, PTH, isobutylmethylxanthine (α phosphodiesterase inhibitor), and phorbol ester, despite intracellular accumulation of cAMP. Yu et al.38 however, found that a calcium antagonist also inhibited PGE2-stimulated resorption. Increasing the extracellular concentration of calcium in cultured OB-enriched cells enhanced the cAMP response to PGE2 and PTH;45 inclusion of verapamil (α calcium antagonist) reduced the size of this cAMP increase, whereas the calcium ionophore A23187 enhanced the response. This implies that calcium has a regulatory function in the cAMP response to these hormones, but the full extent of its role in the control of resorption is poorly understood.
A retrospective analysis of artificial oocyte activation in patients with low or no fertilisation in intracytoplasmic sperm injection cycles
Published in Journal of Obstetrics and Gynaecology, 2022
Kevin K. W. Lam, Jacki Y. Y. Wong, Tak-Ming Cheung, Raymond H. W. Li, Ernest H. Y. Ng, William S. B. Yeung
Calcium ionophores are lipid soluble molecules. They transport calcium ions across the cell membrane which in turn induce a single transient rise in intracellular calcium level. When used for AOA, the concentration of A23187 varies from 5–10 µM (Montag et al. 2012; Lv et al. 2020). Although the concentration of the ready-to-use A23187 reagent is not disclosed by the manufacturer, it has been shown to induce a single rise in intracellular calcium to a peak within two minutes (Nikiforaki et al. 2016). The safety and efficacy of the ready-to-use A23187 has been proven in previous studies (Ebner et al. 2012; Caglar et al. 2015; Ebner et al. 2015). Exposure of A23187 in conjunction with calcium chloride injection together with spermatozoon has also been reported (Vanden Meerschaut et al. 2012). Our data indicated that the performance of two protocols were comparable. The observation is understandable as the injection of calcium chloride and the subsequent A23187 exposure might increase the intracellular calcium concentration to a level higher than that using A23187 alone, both protocols could not generate calcium oscillations (Nikiforaki et al. 2016). To the best of our knowledge, there is no commercially available mouse embryo-tested calcium chloride for AOA. The calcium chloride solution was mainly prepared from research grade chemicals (Vanden Meerschaut et al. 2012; Nikiforaki et al. 2016), the safety of which is in doubt. Based on the current data, AOA should be performed without the concomitant injection of calcium chloride.
Auranofin, a thioredoxin reductase inhibitor, causes platelet death through calcium overload
Published in Platelets, 2019
Auranofin has been reported to induce death of many different cell types. Platelet dysfunction and death was assessed by several approaches. First, the effect of auranofin on the capacity of platelets to respond to stimulation was determined. Platelets were treated with auranofin (10 µM) for up to 2 hours (or DMSO as vehicle control) then stimulated with thrombin (1 U/ml). DMSO-treated platelets underwent rapid and extensive aggregation, as indicated by the decrease in optical density (Figure 1B). In contrast, platelets treated with auranofin for 2 hours did not aggregate. Second, lactate dehydrogenase (LDH) release was determined as a marker of loss of plasma membrane integrity. LDH was detected in the medium following auranofin treatment, whereas treatment with DMSO had no significant effect (Figure 1C). LDH release was also in platelets treated with the Ca2+ ionophore, A23187 (10 µM). Ca2+ ionophores have been previously shown to induce platelet necrosis [19]. Third, treatment with auranofin also resulted in a time-dependent increase in annexin V (AnV) binding, indicative of PS exposure and platelet procoagulant activity (Figure 1D–E). The AnV-positive fraction (AnV+Total) could be resolved into two populations, designated AnV+Med and AnV+High. PS exposure was not due to prolonged platelet incubation at 37 °C, since treatment with DMSO did not induce AnV binding even up to 2 hours (Figure 1F).
Assisted oocyte activation with calcium ionophore 44 hours after intracytoplasmic sperm injection resulting in successful pregnancy
Published in Gynecological Endocrinology, 2020
Haitao Xi, Yanghua Fu, Chang Liu, Xiaosheng Lu, Liucai Sui, Yulu Chen, Junzhao Zhao
During in vitro fertilization, both sperm and ovum need to undergo the process of capacitation. Sperm capacitation could be operated by using A23187 calcium solution or heparin. Calcium ionophore A23187 is a kind of mobile ionophore, which could transport bivalent cation such as calcium ion or magnesium ion into the cells and take two hydrogen ions outside the cells simultaneously. When A23187 is added to the culture medium containing calcium ion, the calcium ion could enter into the cytoplasm quickly. Thus, A23187 is widely used in cell biological research to increase the concentration of free calcium in the cytoplasm.