Brush border membrane vesicles from dipteran midgut: a tool for studies on nutrient absorption

Brush border membrane vesicles (BBMV) from insects midgut can be successfully used to study several membrane phenomena, including nutrient absorption, ions permeability and insecticides mode of action. Midgut BBMV, purified from Musca domestica whole larvae, were used for the functional characterization of leucine transport. The amino acid uptake was accelerated in the presence of sodium or potassium and increased significantly when the extravesicular pH was 5.0, in agreement with the luminal pH in vivo. Radiolabelled leucine uptake was significantly reduced by an excess of cold leucine, histidine, serine and glycine, suggesting that the amino acid transporter is a broad scope carrier that does not recognize proline, glutamine and the dibasic amino acids lysine and arginine. Midgut BBMV were also obtained from homogenization of M. domestica and Bactrocera oleae adults. The final preparations showed a high enrichment in the specific activity of the BBM marker enzymes aminopeptidase N and γ-glutamyl transpeptidase, and were poorly contaminated by basolateral membranes, as indicated by the low specific activities of their marker enzyme Na/K ATPase. Electron microscopy of B. oleae BBM fraction showed the presence of closed vesicles. Similar SDS-PAGE patterns, with numerous distinct bands, were detected for both B. oleae and M. domestica BBMV.