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+).

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