title: Regulation by extracellular Na+ of cytosolic Mg2+ concentration in Mg(2+)-loaded rat sublingual acini.
abstract: The regulation of cytosolic free Mg2+ concentration ([Mg2+]i) in Mg(2+)-loaded rat sublingual mucous acini was examined using the Mg(2+)-sensitive fluorescent indicator mag-fura-2. Loading sublingual acini with 5 mM Mg2+ elevated the [Mg2+]i from 0.35 +/- 0.01 mM to 0.66 +/- 0.01 mM. Removal of extracellular Mg2+ resulted in a significantly faster [Mg2+]i decrease in Mg(2+)-loaded acini than in unloaded acini. Membrane depolarization with high extracellular [K+] and inhibition of P-type ATPases by vanadate did not alter the [Mg2+]i decrease, indicating that the Mg2+ efflux mechanism is not electrogenic. Na(+)-free medium inhibited 80% of the [Mg2+]i decrease suggesting that a Na(+)-dependent Mg2+ efflux pathway mediates the [Mg2+]i decrease. Accordingly, the Na(+)-dependent antiport inhibitor quinidine reduced > 80% of the [Mg2+]i decrease, suggesting that the Na(+)-dependent Mg2+ efflux is mediated by the Na+/Mg2+ antiport system. Mg2+ efflux was also partly driven by K+. The [Mg2+]i decreased was significantly inhibited by carbachol, a muscarinic agonist, but not by cAMP. These results indicate that in sublingual acinar cells a Na(+)-dependent pathway mediates Mg2+ efflux and that muscarinic stimulation may regulate Mg2+ extrusion.
authors.affiliation: Department of Dental Research, University of Rochester, NY 14642, USA.
authors.forename: G H
authors.initials: GH
authors.lastname: Zhang
authors.forename: J E
authors.initials: JE
authors.lastname: Melvin
mesh_terms: D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors; D000818:Animals; D017920:Antiporters / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2 / Q000031:analogs & derivatives; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials; D011802:Quinidine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000502:physiology*; D013361:Sublingual Gland / Q000166:cytology / Q000378:metabolism*; D014638:Vanadates / Q000494:pharmacology
chemical_list: D017920:Antiporters; D005456:Fluorescent Dyes; C046250:sodium-magnesium antiporter; C058776:2-(2-(5-carboxy)oxazole)-5-hydroxy-6-aminobenzofuran-N,N,O-triacetic acid; D014638:Vanadates; D002217:Carbachol; D012964:Sodium; D000242:Cyclic AMP; D000251:Adenosine Triphosphatases; D008274:Magnesium; D011802:Quinidine; D002118:Calcium; D016257:Fura-2