An animal homolog of plant Mep/Amt transporters promotes ammonia excretion by the anal papillae of the disease vector mosquito, Aedes aegypti

Abstract

The transcripts of three putative ammonia (NH3/NH4+) transporters, Rhesus-like glycoproteins AeRh50-1, AeRh50-2 and Amt/Mep-like AeAmt1 were detected in the anal papillae of larval Aedes aegypti. Quantitative PCR studies revealed 12-fold higher transcript levels of AeAmt1 in anal papillae relative to AeRh50-1, and levels of AeRh50-2 were even lower. Immunoblotting revealed AeAmt1 in anal papillae as a preprotein with putative monomeric and trimeric forms. AeAmt1 was immunolocalized to the basal side of the anal papillae epithelium where it co-localized with Na+/K+-ATPase. Ammonium concentration gradients were measured adjacent to anal papillae using the scanning ion-selective electrode technique (SIET) and used to calculate ammonia efflux by the anal papillae. dsRNA-mediated reductions in AeAmt1 decreased ammonia efflux at larval anal papillae and significantly increased ammonia levels in hemolymph, indicating a principal role for AeAmt1 in ammonia excretion. Pharmacological characterization of ammonia transport mechanisms in the anal papillae suggest that, in addition to AeAmt1, the ionomotive pumps V-type H+-ATPase and Na+/K+-ATPase as well as NHE3 are involved in ammonia excretion at the anal papillae.