title: Up-regulation of Na+-dependent Mg2+ transport by nitric oxide and cyclic GMP pathway in renal epithelial cells.
abstract: A putative, Na(+)-dependent Mg(2+) transport pathway controls the intracellular free Mg(2+) concentration ([Mg(2+)](i)) in various mammalian cells. The characteristics of this Mg(2+) transport pathway have not been clarified. Herein, we examined the regulatory mechanism of Na(+)-dependent Mg(2+) efflux in renal epithelial NRK-52E cells. Mg(2+) removal from the extracellular bathing solution induced an Na(+)-dependent [Mg(2+)](i) decrease in Mg(2+) (5 mM)-loaded cells but not in control cells. Amiloride inhibited the [Mg(2+)](i) decrease in a dose-dependent manner (IC(50) = 3 microM). Similarly, atomic absorption spectrophotometry showed that Mg(2+) removal decreased intracellular Mg(2+) content, while it increased Na(+) content. Calphostin C (1 microM), a protein kinase C inhibitor, and genistein, a tyrosine kinase inhibitor (10 microM), blocked the [Mg(2+)](i) decrease. The [Mg(2+)](i) decrease was accompanied by an increase in intracellular nitric oxide (NO) and cyclic GMP contents. (E)-4-methyl-2-[(E)-hydoxyimino]-5-nitro-6-methoxy-3-hexenamide (0.1 mM), an NO donor, and 8-bromo-cyclic GMP (0.1 mM), a membrane-permeable cyclic GMP analogue, accelerated the [Mg(2+)](i) decrease. In contrast, N(G)-monomethyl-L-arginine (L-NMMA, 0.1 mM), an NO competitive inhibitor, and 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ, 10 microM), an NO-sensitive guanylate cyclase inhibitor, significantly blocked the [Mg(2+)](i) decrease. These results indicate that a decrease in extracellular Mg(2+) concentration induces the production of NO and cyclic GMP, which leads to the up-regulation of Na(+)-dependent Mg(2+) efflux.
authors.affiliation: Department of Environmental Biochemistry and Toxicology, University of Shizuoka School of Pharmaceutical Sciences, 52-1 Yada, Shizuoka City, Shizuoka 422-8526, Japan. ikari@u-shizuoka-ken.ac.jp
authors.forename: Akira
authors.initials: A
authors.lastname: Ikari
authors.forename: Kumiko
authors.initials: K
authors.lastname: Nakajima
authors.forename: Sayuri
authors.initials: S
authors.lastname: Taki
authors.forename: Yasunobu
authors.initials: Y
authors.lastname: Suketa
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D006152:Cyclic GMP / Q000378:metabolism*; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D012964:Sodium / Q000378:metabolism*; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*
chemical_list: D009569:Nitric Oxide; D012964:Sodium; D006152:Cyclic GMP; D008274:Magnesium