Electrodiffusive magnesium transport across the intestinal brush border membrane of tilapia (Oreochromis mossambicus)

Mg2+ transport across the brush border of proximal intestinal epithelium of the teleost fish Oreochromis mossambicus was investigated, using Mg-27(2+) to trace movement of Mg2+. Mg2+ uptake in brush border membrane vesicles was stimulated by a K+ diffusion potential (inside negative). Electrodiffusive Mg2+ transport obeyed simple Michaelis-Menten kinetics and was strongly temperature dependent, indicative of a carrier mechanism. The metal ion specificity of this electrodiffusive pathway (inhibition potency order: Co > Mn = Ni > La > Ca > Gd > Ba), predicts a specific role in Mg2+ transport. Competitive inhibition by Co(III) hexammine [Co(NH3)(6)(3 +) ] suggests that this transport system interacts with the solvated Mg ion. We propose that this novel transport system allows the uptake of Mg2+ across the apical brush border membrane, and is involved in transcellular Mg2+ transport. Consequently, the prevailing potential difference across the apical membrane represents a major driving force for intestinal Mg2+ absorption.