STRUCTURE-RELATIONSHIP STUDY OF THE UPTAKE OF ALIPHATIC POLYAMINE COMPOUNDS BY RAT INTESTINAL BRUSH-BORDER MEMBRANE-VESICLES

The effects of lipophilicity, ion-diffusion potential and membrane sur face potential on the uptake of various aliphatic polyamine compounds by rat intestinal brush-border membrane vesicles (BBMV) have been inve stigated. A valinomycin-induced potassium-diffusion potential (inside- negative) stimulated the initial uptake of diamine compounds, and good correlation was observed between lipophilicity and the amount of diff usion potential-dependent transport of the diamines. In contrast, beca use of their much lower lipophilicity, tri- and tetraamine compounds w ere not affected by the diffusion potential. Tetracaine, which can mak e the membrane surface potential more positive, inhibited the transpor t rate of 1,9-nonanediamine, spermidine and spermine by the BBMV. Thes e data suggest that the transport mechanism of diamines is similar to that of monoamine compounds in respect to its dependence on ion-diffus ion potential and on the membrane surface potential. The extent of the effect of ion-diffusion potential on the rate of transport of the dia mines was closely related to the lipophilicity of the diamine. In cont rast, only the surface potential contributed to the transport mechanis m of lower lipophilic tri- and tetraamine compounds.