Role of the choline exchanger in Na-independent Mg efflux from rat erythrocytes |
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Authors: | H Ebel M Hollstein T Günther |
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Institution: | a Institut für Klinische Physiologie, Klinikum Benjamin Franklin, Freie Universität Berlin, Hindenburgdamm 30, 12200 Berlin, Germany b Institut für Molekularbiologie und Biochemie, Klinikum Benjamin Franklin, Freie Universität Berlin, Arnimallee 22, 14195 Berlin, Germany |
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Abstract: | 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 non-selective 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 Kd value for inhibition of 14C]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 14C]choline efflux. |
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Keywords: | Na+-independent Mg2+ efflux Choline exchanger Hemicholinum-3 Cinchona alkaloids Rat erythrocytes |
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