THE TRANSPORT MECHANISMS OF ORGANIC CATIONS AND THEIR ZWITTERIONIC DERIVATIVES ACROSS RAT INTESTINAL BRUSH-BORDER MEMBRANE .2. COMPARISON OF THE MEMBRANE-POTENTIAL EFFECT ON THE UPTAKE BY MEMBRANE-VESICLES

Further investigation of organic cation transport mechanisms were cont inued using rat intestinal brush-border membranes following our previo us report [1,2]. The net uptake of organic cations was superior to tha t of their zwitterionic derivatives. This result agreed with the absor ption behaviour of these compounds from rat intestinal loop. The uptak e of tyramine and 5-benzyloxytryptamine was significantly stimulated b y the valinomycin-generated K+-diffusion potential (inside-negative). On the other hand, the uptake of zwitterionic derivatives was not affe cted by the valinomycin-induced K+-diffusion potential. The voltage-cl amped brush-border membrane vesicles exhibited a complete disappearanc e of the overshoot-uptake of organic cations. Therefore, this permeati on mechanism across the intestinal brush-border membrane seems to be d ifferent from the well-known H+-antiport system of organic cation foun d in other organs such as kidney and liver, and depends upon an inside -negative H+- or K+-diffusion potential.