Intracellular magnesium: transport and regulation in epithelial secretory cells.
The mechanisms of magnesium (Mg2+) transport, the regulation of intracellular Mg2+ concentrations and the relationship between Mg2+ and Ca2+ signaling during the stimulus-secretion coupling process in pancreatic acinar cells and other secretory epithelia are reviewed in this article. Our results demonstrate the existence of a Na+- and ATP-dependent transport system for Mg2+ extrusion from Mg2+-loaded cells. Moreover, employing such different techniques as spectrofluorimetry and atomic absorbance spectroscopy to measure intracellular free magnesium concentration [Mg2+]i from magfura-2-loaded acini and acinar cells and Mg2+ content in effluent samples from perfused pancreatic segments, respectively, confirm that secretagogues such as acetylcholine (ACh) and cholecystokinin-octapeptide (CCK-8) can evoke marked and significant extrusion of Mg2+ which is closely associated with the mobilization of intracellular calcium. These effects may be modulated by different mediators including cAMP, Protein Kinase C and nitric oxide/cGMP. This reduction in [Mg2+]i seems to be a prerequisite for optimal generation and maintenance of the calcium signal and subsequently, the secretion of enzymes, since an increase in extracellular Mg2+ concentration, [Mg2+]o and an increase in [Mg2+]i inhibit secretagogue-induced secretory responses, an effect exerted through a derangement of the calcium signaling events. In conclusion, the evidence presented in this review strongly supports an important modulatory role of magnesium in the control of secretory epithelial cells function.
Yago
M D
MD
Department of Biological Sciences, University of Central Lancashire, Preston, PR1 2HE, England.
Manas
M
M
Singh
J
J
D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism*; D005088:Exocrine Glands / Q000378:metabolism; D006801:Humans; D008274:Magnesium / Q000032:analysis / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D010179:Pancreas / Q000378:metabolism
D008274:Magnesium; D002118:Calcium