Permeability and disruption of the peritrophic matrix and caecal membrane from Aedes aegypti and Anopheles gambiae mosquito larvae

In mosquito larvae, the peritrophic matrix (PM) separates the gut contents from the intestinal epithelium. This report describes a new in vivo assay f or estimating PM permeability. The assay also allows for assessment of the permeability of the caecal membrane, a structure that separates each caecum from the gut lumen. Permeability was estimated by the appearance of fluore scently-labeled dextrans (size range 4,400 to 2 million Dal within the gast ric caecae of mosquito larvae. While the intact peritrophic matrix was impe rmeable to 2 million Da dextran particles, it was permeable to dextran part icles of 148 kDa and smaller. The caecal membrane appears to have considera bly smaller pores, being permeable only to dextrans of 19.5 kDa and smaller . The assay was also used to devise a treatment that disrupts the PM suffic iently to allow the passage of virus-sized particles. Dithiothreitol and to a lesser extent, chitinase were effective in disrupting the PM. Cyclohexim ide had a small effect; Polyoxin D, Pronase and calcofluor did not alter th e permeability to 2 million Da dextran particles. Disruption of the PM is d iscussed in the context of infecting mosquitoes with retroviral transformat ion vectors. (C) 2000 Elsevier Science Ltd. All rights reserved.