a-AMINOISOBUTYRIC ACID TRANSPORT IN THE MIDGUT OF TWO LEPIDOPTERAN LARVAE

1. A net absorption of a-aminoisobutyric acid (AIB) takes place in vitro in the midgut of two lepidopteran larvae, Philosamia cynthia Drury and Bombyx mori L. 2. lnP. cynthia the midgut epithelium accumulates AIB from the lumen, while in the same conditions AIB accumulation is not observed in B. mori midgut cells. 3. In P. cynthia, when the lumen is bathed with a low K solution, the net absorption of AIB is reduced and the intracellular accumulation from the lumen is abolished. 4. Brush border membrane vesicles, prepared from the midgut of both species, show a transient K-dependent concentrative uptake of AIB. 5. The relationship between AIB uptake and AIB concentration in the presence of a transmembrane K gradient was studied in B. mori vesicles and the kinetic constants were calculated. 6. These results confirm that there is a K-amino acid co-transport system on the brush border of columnar cells in the midgut of both larvae.