Secretagogue-evoked changes in intracellular free magnesium concentrations in rat pancreatic acinar cells

1. This study employs the fluorescent dye Mag-Fura-2 acetoxymethyl ester (AM) to measure intracellular free magnesium concentration [Mg2+]i in isolated rat pancreatic acinar cells. Initially a number of protocols were investigated to develop optimal loading conditions for the dye Mag-Fura-2 AM. The procedure yielding cells which showed minimal dye loss and no adverse compartmentalization was adopted for subsequent experiments. 2. The mean resting [Mg2+]i is 1.39 +/- 0.08 mM (n = 39). 3. Acetylcholine (ACh), cholescystokinin-octapeptide (CCK8), carbamylcholine chloride evoked marked reduction in [Mg2+]i in pancreatic acinar cells compared to resting values in the absence of secretagogues. The ACh-evoked decrease in [Mg2+]i was abolished by pre-treatment with atropine. In contrast, noradrenaline, adrenaline and histamine had no significant effect on [Mg2+]i. 4. In acinar cells loaded with the Ca(2+)-sensitive dye, Fura-2 acetoxymethyl ester (AM), ACh stimulation resulted in a marked elevation in intracellular free Ca2+ concentration [Ca2+]i. This response was blocked by pre-treatment with atropine. 5. Atomic absorption spectrophotometry was used to measure Mg2+ levels in effluent samples from pancreatic segments. Stimulation of pancreatic segments with ACh resulted in a marked elevation in Mg2+ concentrations (net efflux). On removal of ACh, Mg2+ concentration returned to resting level followed by a small net influx of Mg2+ into pancreatic tissue. 6. The results demonstrate that secretagogue-evoked alteration in [Mg2+]i may occur concurrently with Mg2+ release from pancreatic tissue.