Magnesium transport in ferret red cells.
1. Mg2+ efflux from ferret red cells into a nominally Mg2(+)-free medium is 41 +/- 2 mumol (l cell)-1 h-1. The properties of Mg2+ transport can be measured in these cells without the need for Mg2+ loading. 2. Amiloride, quinidine, imipramine and external divalent cations partially inhibit Mg2+ efflux. Maximal inhibition by these agents is about 60-70% suggesting that at least two Mg2+ transport pathways exist. 3. As external Na+ is replaced by choline or N-methyl-D-glucamine Mg2+ efflux is first stimulated, reaching a peak when external [Na+] ([Na+]o) is about 10 mM, and then inhibited. Mg2+ transport reverses direction so net Mg2+ uptake occurs when [Na+]o is reduced below 1 mM. 4. Mg2+ efflux is stimulated when 0.1 mM-EDTA is added to the medium only when [Na+]o is low. 5. Reduction of cell ATP content to about 20 mumol (l cell)-1 by treating cells with 2-deoxyglucose stimulates Mg2+ efflux measured over the 2 h period following depletion. 6. Substantial Mg2+ influx can be observed in ferret red cells when they are incubated in media containing 10 mM-Mg2+. Influx is stimulated by reducing [Na+]o to 10 mM. Further reduction of [Na+]o to below 1 mM reduces Mg2+ uptake. A component of uptake is inhibited by external Co2+. 7. Na(+)-Mg2+ antiport may account for a substantial component of Mg2+ transport in ferret red cells. The direction of transport can be reversed by sufficiently lowering [Na+]o or by increasing external [Mg2+]. Analysis of the conditions at which transport reverses direction suggests transport with a stoichiometry of 1 Na+:1 Mg2+. Antiport with this stoichiometry would also explain maintenance of the physiological level of intracellular ionized Mg2+ in these cells.
Flatman
P W
PW
Department of Physiology, University Medical School, Edinburgh.
Smith
L M
LM
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002413:Cations, Divalent / Q000494:pharmacology; D002794:Choline / Q000494:pharmacology; D003035:Cobalt / Q000494:pharmacology; D003847:Deoxyglucose / Q000494:pharmacology; D003864:Depression, Chemical; D004912:Erythrocytes / Q000378:metabolism*; D005289:Ferrets / Q000097:blood*; D007099:Imipramine / Q000494:pharmacology; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism*; D008536:Meglumine / Q000494:pharmacology; D011802:Quinidine / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D013696:Temperature
D002413:Cations, Divalent; D003035:Cobalt; D008536:Meglumine; D000584:Amiloride; D003847:Deoxyglucose; D012964:Sodium; D008274:Magnesium; D011802:Quinidine; D002794:Choline; D007099:Imipramine