Links between osmoregulation and nitrogen-excretion in insects and crustaceans

Abstract

The epithelia involved in ionoregulation and detoxification in crustaceans and insects are quite distinct: the gills, hepatopancreas, and antennal gland serve these functions in crustaceans, whereas the Malpighian tubules, hindgut, and, to some extent, the midgut, are involved in insects. This article compares the means by which the Na+/K+-ATPase and the vacuolar type H+-ATPase are used to energize ionoregulatory processes in both groups. The vacuolar H+-ATPase is particularly important as a generator of both H+ gradients and transmembrane electrical gradients that can be used to energize electroneutral or electrogenic exchange of Na+ and/or K+ for H+. In addition to cation:proton antiporters, epithelia in both groups depend upon the activity of Na+:K+:2Cl- cotransporters, Cl-/HCO3- exchangers, and channels for K+ and Cl- for transepithelial ion transport. This article also contrasts the dominant role of ammonia as the primary nitrogenous waste in crustaceans, with the excretion of ammonia, uric acid, or both in insects.