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  • 1
    Electronic Resource
    Electronic Resource
    Cytosolic free Ca2+ in insulin secreting cells and its regulation by isolated organelles (1984)
    Springer
    Cellular and molecular life sciences 40 (1984), S. 1052-1060 
    Details
    ISSN: 1420-9071
    Keywords: Pancreatic B-cell ; insulin secretion ; cytosolic free Ca2+
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The role of Ca2+ in secretagogue-induced insulin release is documented not only by the measurements of45Ca fluxes in pancreatic islets, but also, by direct monitoring of cytosolic free Ca2+, [Ca2+]i. As demonstrated, using the fluorescent indicator quin 2, glyceraldehyde, carbamylcholine and alanine raise [Ca2+]i in the insulin secreting cell line RINm5F, whereas glucose has a similar effect in pancreatic islet cells. The regulation of cellular Ca2+ homeostasis by organelles from a rat insulinoma, was investigated with a Ca2+ selective electrode. The results suggest that both the endoplasmic reticulum and the mitochondria participate in this regulation, albeit at different Ca2+ concentrations. By contrast, the secretory granules do not appear to be involved in the short-term regulation of [Ca2+]i. Evidence is presented that inositol 1,4,5-trisphosphate, which is shown to mobilize Ca2+ from the endoplasmic reticulum, is acting as an intracellular mediator in the stimulation of insulin release.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01971451
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Stimulatory and inhibitory effects of cyclic AMP on pancreatic glucagon release from monolayer cultures and the controlling role of calcium (1976)
    Springer
    Diabetologia 12 (1976), S. 269-277 
    Details
    ISSN: 1432-0428
    Keywords: Monolayer culture ; glucagon release ; cyclic AMP ; Ca++ ; cholera toxin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary When glucagon release from monolayer cultures of newborn rat pancreas was measured over four hours in media containing 2.5 mM Ca++, a significant cyclic AMP-related inhibition of release was observed. This was noted whether intracellular cyclic AMP levels were raised by the addition of exogenous cyclic AMP or dibutyryl cyclic AMP, by phosphodiesterase inhibition with theophylline, or by the stimulation of adenylate cyclase with cholera toxin. The inhibition was concentration dependent for cyclic AMP and could not be reproduced by the addition of AMP, ADP or ATP. Adenosine also inhibited glucagon release while ATP was stimulatory. From time course studies it appeared that the inhibitory effects of cyclic AMP and cholera toxin were progressive after two hours of incubation. With cholera toxin an early stimulation of glucagon release was observed. The effects of cyclic AMP and cholera toxin on argininestimulated glucagon release were to stimulate further the glucagon release during the first hour of the incubation. Thus, the effects of raising intracellular cyclic AMP levels were biphasic in that both an early stimulation and a late inhibition of glucagon release were observed. In examining the nature of these responses a remarkable controlling role for Ca++ was uncovered: at Ca++ concentrations of 0.3 mM and lower no effect of cyclic AMP on glucagon release was found. With 1 mM Ca++ in the medium cyclic AMP stimulated glucagon release early (30 min) and thereafter had no further effect. In the presence of 2.5 mM Ca++ cyclic AMP did not stimulate early but did cause the delayed inhibition of release. It is concluded that the effect of cyclic AMP on glucagon release can be either stimulatory or inhibitory depending upon the Ca++ concentration of the medium and the duration of exposure to raised cyclic AMP levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00422095
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    Paper (German National Licenses)
    Fulltext
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