Role of the choline exchanger in Na(+)-independent Mg(2+) efflux from rat erythrocytes.
Two types of Na(+)-independent Mg(2+) efflux exist in erythrocytes: (1) Mg(2+) efflux in sucrose medium and (2) Mg(2+) efflux in high Cl(-) media such as KCl-, LiCl- or choline Cl-medium. The mechanism of Na(+)-independent Mg(2+) 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(+)/Mg(2+)-, Na(+)/Ca(2+)- and K(+)(Na(+))/H(+) antiport, Ca(2+)-activated K(+) channel and Mg(2+) leak flux. We suggest that, in choline Cl medium, Na(+)-independent Mg(2+) efflux can be performed by non-selective transport via the choline exchanger. This was supported through inhibition of Mg(2+) 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 Mg(2+) to the same degree. The K(d) value for inhibition of [(14)C]choline efflux and for inhibition of Mg(2+) efflux by HC-3 were the same within the experimental error. Inhibition of choline efflux and of Mg(2+) efflux in choline medium occurred as follows: quinine>cinchonine>HC-3>DoTMA. Mg(2+) efflux was reduced to the same degree by these inhibitors as was the [(14)C]choline efflux.
Ebel
H
H
Institut für Klinische Physiologie, Klinikum Benjamin Franklin, Freie Universität Berlin, Germany. hans.ebel@medizin.fu-berlin.de
Hollstein
M
M
Gunther
T
T
D000818:Animals; D002794:Choline / Q000378:metabolism*; D002930:Cinchona Alkaloids / Q000494:pharmacology; D015536:Down-Regulation; D004912:Erythrocytes / Q000378:metabolism*; D006426:Hemicholinium 3 / Q000494:pharmacology; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D049990:Membrane Transport Modulators; D026901:Membrane Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar
D002930:Cinchona Alkaloids; D049990:Membrane Transport Modulators; D026901:Membrane Transport Proteins; D000644:Quaternary Ammonium Compounds; C065637:choline transporter; D006426:Hemicholinium 3; C022806:dodecyltrimethylammonium; D008274:Magnesium; D002794:Choline