Role of the choline exchanger in Na+-independent Mg2+ efflux from rat erythrocytes

Two types of Na+-independent Mg2+ efflux exist in erythrocytes: (1) Mg2+ efflux in sucrose medium and (2) Mg2+ efflux in high Cl- media such as KCl-, LiCl- or choline Cl-medium. The mechanism of Na+-independent Mg2+ efflux in choline Cl medium was investigated in this study. Non-selective transport by the following transport mechanisms has been excluded: K+,Cl-- and Na+, K+, Cl--symport, Na+/H+-, Na+/Mg2+-, Na+/Ca2+ - and K+(Na+)/H+ antiport, Ca2+-activated K+ channel and Mg2+ leak flux. We suggest that, in choline Cl medium, Na+-independent Mg2+ efflux can be performed by nonselective transport via the choline exchanger. This was supported through inhibition of Mg2+ efflux by hemicholinum-3 (HC-3), dodecyltrimethylammonium bromide (DoTMA) and cinchona alkaloids, which are inhibitors of the choline exchanger. Increasing concentrations of HC-3 inhibited the efflux of choline and efflux of Mg2+ to the same degree. The K-d value for inhibition of [C-14]choline efflux and for inhibition of Mg2+ efflux by HC-3 were the same within the experimental error. Inhibition of choline efflux and of Mg2+ efflux in choline medium occurred as follows: quinine > cinchonine > HC-3 > DoTMA. Mg2+ efflux was reduced to the same degree by these inhibitors as was the [C-14]choline efflux. (C) 2002 Elsevier Science B.V. All rights reserved.