The mechanisms of magnesium (Mg2+) transport, the regulation of intracellul
ar 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 dem
onstrate the existence of a Na+ - and ATP-dependent transport system for Mg
2+ extrusion from Mg2+-loaded cells. Moreover, employing such different tec
hniques 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 acety
lcholine (ACh) and cholecystokinin-octapeptide (CCK-8) can evoke marked and
significant extrusion of Mg2+ which is closely associated with the mobiliz
ation of intracellular calcium. These effects may be modulated by different
mediators including cAMP, Protein Kinase C and nitric oxide/cGMP. This red
uction in [Mg2+](i) seems to be a prerequisite for optimal generation and m
aintenance of the calcium signal and subsequently, the secretion of enzymes
, since an increase in extracellular Mg2+ concentration, [Mg2+](o) and an i
ncrease in [Mg2+](i) inhibit secretagogue-induced secretory responses, an e
ffect exerted through a derangement of the calcium signaling events. In con
clusion, the evidence presented in this review strongly supports an importa
nt modulatory role of magnesium in the control of secretory epithelial cell
s function.