Calcium ionophore, A23187, and

Br > Cl > I. This conductance was not time-dependent. On the other hand, Cl conductance stimulated by the Ca2+ ionophore A23187 (2.5 pM) or elevation in the free Ca2+ levels in the pipet from 100 to 500 nM was time-dependent and exhibited a nonlinear current-voltage relationship that was outwardly rectifying. The permselectivity of this Ca2+-stimulated conductance was 1 > Br > cr, distinguishing it from the cAMP-stimulated Cfr conductance. As both calcium ionophore A23187 and cAMP were shown to elevate the Cl conductance of the cornea, it is quite likely that these two types of Cr channels are present in the corneal epithelium [96,106,114],... 

Horse platelets contain a large nonmetabohe pool of serotonin and adenine nucleotides within dense bodies (White et al. 1976). Calcium ionophore (A23187) and high doses of thrmnbin (0.4 unitsAnl), but not collagen, ADP, or arachadonic acid, induced secretion of ATP and/or C-serotonin (Weiss et al. 1990, Boudreaux et al. 1988). 

Values are presented as mU/min/mg and mean (SEM) of 4-6 muscles. Muscles were either Incubated without any further treatment, stimulated for 30 min with repetitive tetanii or treated with the calcium ionophore (A23187 - 20 /im) for 30 min. Data presented represent efflux over 90-120 min post-treatment. Animals were fed either a vitamin E-deficient or vitamin E-supplemented diet (Phoenix et al., 1990) for 6 weeks prior to study. Data derived from O Farrell (1994). 

MF effects on FA relatives and healthy donors. (Fanconi anemia is an autosomal recessive disease associated with the overproduction of free radicals, Chapter 31.) It has been shown earlier [215] that FA leukocytes produce the enhanced amount of hydroxyl or hydroxyl-like free radicals, which are probably formed by the Fenton reaction. It was suggested that MF would be able to accelerate hydroxyl radical production by FA leukocytes. Indeed, we found that MF significantly enhanced luminol-amplified CL produced by non-stimulated and PMA-stimulated FA leukocytes but did not affect at all oxygen radical production by leukocytes from FA relatives and healthy donors (Table 21.3). It is interesting that MF did not also affect the calcium ionophore A23187-stimulated CL by FA leukocytes, indicating the absence of the calcium-mediated mechanism of MF activity, at least for FA leukocytes. 

Interestingly, pretreatment of isolated rat peritoneal mast cells with NT desensitizes the cells to the subsequent stimulation by compound 48/80 (Figure 4.3). However, the desensitized cells are still responsive to stimulation by the calcium ionophore, A23187, in the presence of Ca (Figure 4.3). A similar observation has been made when compound 48/80 and the peptides,... 

The histamine- and leukotriene B4-releasing potential of the RCBPA P743 has been investigated in vitro on the RBL-2H3 mast cell line [25]. RBL-2H3 cells (with permission of Dr RP Siraganian, National Institutes of Health, Bethesda, MD, USA) were replated on Eagle s minimum essential medium and incubated for 30 minutes at 37 °C in 5% CO2 with the test-solutions. Calcium ionophore A23187 was used as a positive control. The viability of mast cells was determined by means of a quantitative colorimetric assay that is based on the abiUty of viable cells to cleave the reagent MTT [33]. 

In contrast to the reports by Wang et al. (1997) and Grant et al. (1994), (see page 28) it was also reported that H-7 and staurosporine blocked apoptosis following induction by ara-C in HL-60 cells (Kharbanda, et al, 1991). The calcium ionophore A23187 induced apoptosis in immature mouse thymocytes. H-7 inhibited the DNA fragmentation and cell death (Kizaki et al.. 

APP cleavage to occur (Shi et al., 2001), and removal is carried out by furin, a member of the pro-protein convertase enzymes (Bennett et al., 2000). Furin is a calcium dependent protease and so increases in calcium lead to an increase in activity. Treatment of cells with a calcium ionophore (A23187), which depleted intracellular stores of calcium, leads to a reduction in both furin and BACE activity (Bennett et al., 2000) and thus demonstrates one pathway through how intracellular calcium can regulate A 3 production through BACE. 

Studies with ovarian cells have also shown that extracellular calcium is required to give maximum steroidogenesis [29]. The calcium channel blockers, verapamil or diltiazem also suppressed LH-stimulated progesterone production. The calcium ionophore A23187 significantly enhanced the stimulatory effects of LH. Recently it was shown that FSH, prostaglandin E2 and F2 have distinct effects on steady state calcium exchange in ovarian cells [30]. 

Table 13. Inhibition of TXBi-Release from Human Platelets Stimulated with Calcium Ionophore A23187 (1.8 x 10 M) by Budlejasaponin IV and Sandrosaponin L...

Burke, L.A., Crea, A.E., Wilkinson, J.R, Arm, J.P., Spur, B.W. and Lee, T.H. (1990). Comparison of the generation of platelet-activating fector and leukotriene C in human eosinophils stimulated by unopsonized zymosan and by the calcium ionophore A23187 the effects of nedocromil sodium. J. Allergy Clin. Immunol. 85, 26-35. 

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