Meeting Abstract
The functional kidney in insects is comprised of the Malpighian tubules and hindgut. Together, these tissues play preeminent roles in osmoregulation and excretion. In crustaceans, the gills contribute to multiple processes, including osmotic and ionic regulation, nitrogenous waste excretion, pH homeostasis and gas exchange. Antennal and maxillary glands constitute the principal crustacean excretory organs. Uric acid is the primary nitrogenous waste in insects, but ammonia may also make an important contribution. By contrast, crustaceans have retained ammonotely, even in terrestrial groups. Both the V-type H+-ATPase and the Na+/K+ ATPase are implicated as the energizers of transepithelial ion transport in the crustacean gill. In insect Malpighian tubules, however, the V-ATPase plays the pivotal role, perhaps as a consequence of coevolution of insects and flowering plants, resulting in a high K, low Na diet for most insects. The presence of high levels of allelochemicals in plants has also lead to the development of extraordinary capacities for detoxification and excretion by the gut and Malpighian tubules of insects. Ingestion of experimental diets containing high levels of potential toxins is correlated with increases in gene expression for both detoxification enzymes and toxin transporters in the Malpighian tubules of fruit flies. Recent studies of tubule toxin transport have made use of RNAi knockdown or P-element insertion mutation of organic anion transporter genes as a means of identifying the transporters involved. The urinary bladder of the crustacean antennal gland and the insect Malpighian tubule can provide useful models for understanding mechanisms of toxin transport by their functional analogue, the vertebrate proximal kidney tubule.
