Na +-dependent and Na +-independent transport of l-arginine and l-alanine across dog intestinal brush border membrane vesicles

We prepared intestinal brush border membrane vesicles (BBMVs) from beagle dogs fed a commercial diet (protein content: 24–26%), and investigated the characteristics of transport for basic and neutral amino acids across the intestinal BBMVs. To determined the kinetic parameters for l-arginine and l-alanine uptake, their total uptake was resolved into three routes: (1) Na +-dependent carrier-mediated transport; (2) Na +-independent carrier-mediated transport; and (3) simple diffusion. We could observe subtle, but clear-cut, Na +-dependent basic amino acid transport for the first time among studies with intestinal BBMVs prepared from mammals fed a normal diet. The Na +-dependent system for l-arginine transport can be best characterized as ‘low affinity, low capacity’, in contrast to that for l-alanine transport, which is ‘low affinity, high capacity’. Maximal velocities of the Na +-dependent carrier-mediated transport are estimated to be higher for both l-arginine and l-alanine in dog intestinal BBMVs than in rabbit intestinal BBMVs reported previously. These results suggest that food habit of mammals is an important factor to decide the characteristic of system B 0,+, a Na +-dependent carrier-mediated transport system common to basic and neutral amino acids across intestinal brush border membranes, as is protein content of the diet.