Mjc. Bijvelds et al., MAGNESIUM TRANSPORT ACROSS THE BASOLATERAL PLASMA-MEMBRANE OF THE FISH ENTEROCYTE, The Journal of membrane biology, 154(3), 1996, pp. 217-225
In tilapia (Oreochromis mossambicus) intestine, Mg2+ transport across
the epithelium involves a transcellular, Na+- and Na+/K+-ATPase depend
ent pathway. In our search for the Mg2+ extrusion mechanism of the bas
olateral compartment of the enterocyte, we could exclude Na+/Mg2+ anti
port or ATP-driven transport. Evidence is provided, however, that Mg2 movement across the membrane is coupled to anion transport. In basola
teral plasma membrane vesicles, an inwardly directed CT gradient stimu
lated Mg2+ uptake (as followed with the radionuclide Mg-27) twofold. A
s Cl--stimulated uptake was inhibited by the detergent saponin and by
the ionophore A23187, Mg2+ may be accumulated intravesicularly above c
hemical equilibrium. Valinomycin did not affect uptake, suggesting tha
t electroneutral symport activity occurred. The involvement of anion c
oupled transport was further indicated by the inhibition of Mg2+ uptak
e by the stilbene derivative, 4,4'-diisothiocyanato-stilbene-2,2'-disu
lfonic acid. Kinetic analyses of the Cl--stimulated Mg2+ uptake yielde
d a K-m (Mg2+) of 6.08 +/- 1.29 mmol . l(-1) and a K-m (Cl-) of 26.5 /- 6.5 mmol . l(-1), compatible with transport activity at intracellul
ar Mg2+- and Cl--levels. We propose that Mg2+ absorption in the tilapi
a intestine involves an electrically neutral anion symport mechanism.