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  • Title: Complex pattern of inhibition by Mg2+ of exocytosis from permeabilised eosinophils.
    Author: Larbi KY, Gomperts BD.
    Journal: Cell Calcium; 1997 Mar; 21(3):213-9. PubMed ID: 9105730.
    Abstract:
    Inhibition by Mg2+ ions of exocytotic secretion from permeabilised eosinophils, stimulated by Ca2+ and GTP gamma S, and in the presence and absence of ATP, has been examined. While Mg2+ inhibits release of aryl sulphatase, hexosaminidase and peroxidase, we found no evidence that this occurs by competition at a Ca(2+)-binding site. On the other hand, the IC50 for Mg2+ approximates a simple inverse relationship to EC50 for GTP gamma S over a wide range of concentrations, indicative of a possible competition with events directly controlled by a GTP-binding protein. However, for secretion stimulated by GTP gamma S in the absence of Ca2+ (which necessitates provision of ATP), the effect of Mg2+ becomes biphasic. Initially, secretion is dependent on the presence of Mg2+ as a component of the complex ligand Mg.ATP. At high concentrations, Mg2+ inhibits secretion and the IC50 was found to be fixed at a concentration of about 8 mM regardless of the strength of the stimulus. The presence of ATP appears to divert the site of inhibition due to Mg2+.
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