1,721,814 research outputs found
The mechanism of action of ionophore A 23187 on guinea pig intestinal smooth muscle
No full text The cation ionophore A 23187 behaves similarly to the potent muscarinic agonist, cis-2-methyl-4-dimethylaminomethyl-1,3-dioxolane methiodide (CD) in guinea pig ileal longitudinal smooth muscle generating contractile responses that are gradedly sensitive to the concentrations of Ca2+ext and Na+ext. A 23187 and CD responses are insensitive to tetrodotoxin and A 23187 responses are insensitive to atropine. The responses to CD, A 23187, and veratridine are all similarly sensitive to the calcium antagonists D 600 and BAY-1040. D 600 failed to antagonize the ability of A 23187 to transport Ca2+ in a toluene-butanol: water two-phase system. It is suggested that in guinea pig ileal smooth muscle A 23187 does not translocate Ca2+ext exclusively but serves also to activate Ca2+ channels perhaps by an initial depolarizing Na+ entry. </jats:p
The Total Synthesis of A-23187 and Related Enantioselective Aldol Condensations
No full textA-23187 is a calcium specific ionophore which was isolated from Streptomyces chartreusis. The total synthesis of A-23187 and synthesis of related diacid ionophores are discussed.
[Chemical structure included in scanned thesis' Abstract, p. v.]
The synthetic approach used for A-23187 required stereoselective aldol condensations. In this regard, the development of enantioselective aldol condensations with boron enolates is detailed. The general applications of such condensations are also discussed.</p
The effects of the ionophore A-23187 on the rat vas deferens
No full text The calcium ionophore A-23187 induced spontaneous, rhythmic contractions in the rat isolated vas deferens in a concentration-dependent manner. Contractions were blocked by phentolamine and were abolished following pretreatment with reserpine. In tissues preloaded with [3H]noradrenaline, A-23187 (10 μM) caused a time-dependent increase in the release of tritium. The findings suggest that A-23187-induced contractions in the rat vas deferens are secondary to the release of endogenous noradrenaline from the adrenergic nerves, as are contractions induced in this preparation by X-537A (another calcium ionophore) described earlier by other investigators. </jats:p
Stimulation of GLUT-1 glucose transporter expression in response to exposure to calcium ionophore A-23187
No full textWe tested the hypothesis that an increase in cytosolic calcium concentration stimulates glucose transporter isoform (GLUT-1) gene expression. Exposure of a rat liver cell line (Clone 9) to 3 microM A-23187 for 12 h resulted in 3-, 5-, and 10-fold increases in cytochalasin B-inhibitable 3-O-methyl-D-glucose transport, GLUT-1 protein, and GLUT-1 mRNA content, respectively. The induction of GLUT-1 mRNA in response to A-23187 is not preceded by a significant decrease in cell ATP content. This induction is prevented by 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid in conjunction with ethylene glycol-bis(beta-aminoethyl ether)-N,N, N',N'-tetraacetic acid. To investigate the mechanism of GLUT-1 mRNA induction, we found that exposure to A-23187 stabilized GLUT-1 mRNA: with the employment of actinomycin D, GLUT-1 mRNA had a half-life of 1.5 and 5.5 h in control and A-23187-treated cells, respectively. In nuclear run-on assays, the rate of GLUT-1 gene transcription was stimulated 1.5- to 1.7-fold in nuclei isolated from cells exposed to A-23187 for either 30 min or 2 h. These results demonstrate that exposure to A-23187 stimulates GLUT-1 gene expression and that the increase in GLUT-1 mRNA content is mediated in part by enhanced GLUT-1 gene transcription as well as decreased GLUT-1 mRNA degradation. The increase in GLUT-1 mRNA content, in turn, is associated with increased cell GLUT-1 content and enhanced glucose transport.</jats:p
Calcium ionophore A-23187 inhibits the secretion of β-hexosaminidase from the GG2EE mouse macrophage cell line
No full textSecretion of the lysosomal enzyme β-N-acetylhexosaminidase is inhibited by calcium ionophore A-23187 in the GG2EE macrophage cell line. Such inhibition is time and dose dependent. Calcium ionophore A-23187 treatment causes a change in the pattern of hexosaminidase isoenzymes detectable in the cell extract, as assessed by DEAE-cellulose chromatography. In particular, control cells show two hexosaminidase isoenzymes corresponding to hexosaminidase A and B, whereas cells treated with calcium ionophore A-23187 express a third isoenzyme form with properties similar to hexosaminidase S
The Action of the Ionophores, X-537A and A-23187, on Smooth Muscle
No full text The cation ionophore X-537A in the concentration range of 10−6 to 3 × 10−5 M produced contractions in the rat and guinea-pig vas deferens. No contractile effect was produced in either of the vasa deferentia preparations by the ionophore A-23187 in the concentration range of 10−7 to 5 × 10−5 M. In contrast, X-537A had no contractile effect on the guinea-pig ileal longitudinal smooth muscle while A-23187 produced a dose and [Ca2+] dependent contraction.The contractile effect of X-537A in the vasa deferentia preparations is abolished by phenoxybenzamine or prior reserpine treatment and is therefore attributed to the release of norepinephrine. The effect of A-23187 in the intestinal smooth muscle is attributed to a direct Ca2+ transporting action since its contractile effect is unaffected by histamine, acetylcholine, or 5-hydroxytryptamine antagonists. </jats:p
In SHR aorta, calcium ionophore A-23187 releases prostacyclin and thromboxane A2 as endothelium-derived contracting factors
No full textIn mature spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY), acetylcholine and the calcium ionophore A-23187 release endothelium-derived contracting factors (EDCFs), cyclooxygenase derivatives that activate thromboxane-endoperoxide (TP) receptors on vascular smooth muscle. The EDCFs released by acetylcholine are most likely prostacyclin and prostaglandin (PG)H2, whereas those released by A-23187 remain to be identified. Isometric tension and the release of PGs were measured in rings of isolated aortas of WKY and SHR. A-23187 evoked the endothelium-dependent release of prostacyclin, thromboxane A2, PGF2α, PGE 2, and possibly PGH2 (PGI2 ≫ thromboxane A2 = PGF2α = PGE2). In SHR aortas, the release of prostacyclin and thromboxane A2 was significantly larger in response to A-23187 than to acetylcholine. In response to the calcium ionophore, the release of thromboxane A2 was significantly larger in aortas of SHR than in those of WKY. In both strains of rat, the inhibition of cyclooxygenase-1 prevented the release of PGs and the occurrence of endothelium-dependent contractions. Dazoxiben, the thromboxane synthase inhibitor, abolished the A-23187-dependent production of thromboxane A 2 and inhibited by approximately one-half the endothelium-dependent contractions. U-51605, an inhibitor of PGI synthase, reduced the release of prostacyclin elicited by A-23187 but induced a parallel increase in the production of PGE2 and PGF2α, suggestive of a PGH2 spillover, which was associated with the enhancement of the endothelium-dependent contractions. These results indicate that in the aorta of SHR and WKY, the endothelium-dependent contractions elicited by A-23187 involve the release of thromboxane A2 and prostacyclin with a most likely concomitant contribution of PGH2. Copyright © 2006 the American Physiological Society.link_to_subscribed_fulltex
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Calcium ionophore A-23187 inhibits the secretion of β-hexosaminidase from the GG2EE mouse macrophage cell line
No full textSecretion of the lysosomal enzyme β-N-acetylhexosaminidase is inhibited by calcium ionophore A-23187 in the GG2EE macrophage cell line. Such inhibition is time and dose dependent. Calcium ionophore A-23187 treatment causes a change in the pattern of hexosaminidase isoenzymes detectable in the cell extract, as assessed by DEAE-cellulose chromatography. In particular, control cells show two hexosaminidase isoenzymes corresponding to hexosaminidase A and B, whereas cells treated with calcium ionophore A-23187 express a third isoenzyme form with properties similar to hexosaminidase S
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