Electrogenic k+-basic amino-acid cotransport in the midgut of lepidopteran larvae

Experiments performed on isolated midgut demonstrate that the model proposed for the absorption of neutral amino acids in the K+-transporting intestinal epithelium of lepidopteran larvae applies also to the transport of the basic amino acids histidine and lysine. The characteristics of these K+-basic amino-acid cotransports have been studied in brush-border membrane vesicles. Histidine and lysine are transported by different transport agencies, which share, to a different degree, a high sensitivity to transmembrane electrical potential difference. Kinetic analysis showed that Km for histidine and lysine increased 10-fold and three-fold, respectively, whereas Vmax was only slightly modified when the electrical potential difference was abolished. The relationship between potassium concentration and histidine uptake indicates a cooperative binding of more than one potassium to the transporter. Countertransport experiments with glutamine as elicitor show that histidine and glutamine are transported through the same system. © 1985 Springer-Verlag.