Sulphate transport by rat ileum. Effect of molybdate and other anions

Kinetic constants for SO₄^2? transport by upper and lower rat ileum in vitro have been determined by computer fitting of rate vs concentration data obtained using the everted sac technique. MoO₄^2? inhibition of this transport is competitive, and kinetic constants for the inhibition were similarly determined. Transport is also inhibited by the anions WO₄^2?, S₂O₃^2? and SeO₄^2?, in the order $\text{S}{}_2\text{O}{}_3{}^{\mathrm{2?}}\text{> SeO}{}_4{}^{\mathrm{2?}}\text{≧ MoO}{}_4{}^{\mathrm{2?}}\text{> WO}{}_4{}^{\mathrm{2?}}$. These anions have no effect on the transport of l-valine. Low SO₄^2? transport rates were observed in sacs from animals fed a high-molybdenum diet. The significance of the results with respect to the problem of molybdate toxicity in animals is discussed, and related to the known protective effect of SO₄^2?.