INSECT ION HOMEOSTASIS.

The constant composition of body fluids in insects is maintained by the cooperative interaction of gastrointestinal and urinary tissues. Water follows ionic movements, which are driven by the basolateral Na+/K+-ATPase and/or the apical 'K+(or Na+) pump'. The latter now is thought to be the functional expression of a parallel arrangement of a proton-motive V-ATPase and a K+(or Na+)/nH+ antiport. This review focuses on the pathways for the movement of monovalent inorganic ions through epithelia involved in ion homeostasis. A graphical summary compares the principal findings with respect to cation secretion in lepidopteran caterpillar midgut goblet cells (K+) and in brush-border cells of Malpighian tubules (K+, Na+).