Uptake characteristics of polyamines into rat intestinal brush-border membrane

The uptake characteristics of polyamines, such as spermine, spermidine and putrescine, have been investigated using brush-border membrane vesicles isolated from the small intestine of rats. The uptake of these polyamines into the membrane vesicles was high and the order of uptake was spermine greater than spermidine greater than putrescine at medium pH 7.5, respectively. The medium pH considerably affected the uptake of these polyamines and the amount of uptake increased remarkably with an increase of the medium pH (pH 7.5 or 8.0 greater than pH 5.5). An inward Na+ gradient did not stimulate the uptake rate of any of these polyamines. We have also examined the binding behaviour to the membrane lipid, phospholipids and total lipid, and there was a good correlation in the binding properties, pH-dependency and uptake activity, between the liposomes and brush-border membrane vesicles. These results suggest that the uptake of the polyamine into the vesicles consisted of rapid binding to the outside intestinal surface and slower binding to the inside membrane after permeation. Furthermore, findings from experiments concerning the mutual inhibition among these polyamines and concerning the effect of other polycations, having 2-5 amines in number, on the uptake of spermine, suggest that the number of amino groups in the polyamine molecules plays an important role in the uptake process into the brush-border membrane vesicles.