Insulin secretagogues induce Ca(2+)-like changes in cytoplasmic Mg2+ in pancreatic beta-cells.
The effects of insulin secretagogues on the cytoplasmic Mg2+ concentration ([Mg2+]i) of pancreatic beta-cells were studied in suspensions and in individual beta-cells using dual-wavelength fluorometry and the indicator mag-fura-2. Average [Mg2+]i was in the 800-900 microM range in a medium containing 3 mM glucose. When the sugar concentration was raised to 20 mM, the cells reacted with an initial lowering of [Mg2+]i followed by an increase. The sugar apparently also stimulated leakage of the Mg2+ indicator. Addition of 100 microM tolbutamide or raising the K+ concentration by 25 mM caused relatively rapid increases of [Mg2+]i. Methoxyverapamil prevented the [Mg2+]i-increasing actions of glucose, K+ and tolbutamide. The greatest change in [Mg2+]i was obtained when beta-cells were exposed to 100 microM carbachol. In this case there was a more than 10% lowering, which was reversed upon removal of the agonist. Measurements of [Mg2+]i are important not only for understanding fluctuations of this ion, but may also aid to elucidate the mechanisms involved in the regulation of cytoplasmic Ca2+.
Gylfe
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Department of Medical Cell Biology, Uppsala University, Sweden.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D005947:Glucose / Q000502:physiology; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism*; D051379:Mice; D014044:Tolbutamide / Q000494:pharmacology
D007328:Insulin; D002217:Carbachol; D014044:Tolbutamide; D008274:Magnesium; D005947:Glucose; D002118:Calcium