The drosophila NKCC Ncc69 is required for normal renal tubule function

Epithelial ion transport is essential to renal homeostatic function, and it is dysregulated in several diseases, such as hypertension. An understanding of the insect renal (Malpighian) tubule yields insights into conserved epithelial ion transport processes in higher organisms and also has implications for the control of insect infectious disease vectors. Here, we examine the role of the Na⁺-K⁺-2Cl~ (NKCC) cotransporter Ncc69 in Drosophila tubule function. Ncc69 mutant tubules have decreased rates of fluid secretion and K⁺ flux, and these phenotypes were rescued by expression of wild-type Ncc69 in the principal cells of the tubule. Na⁺ flux was unaltered in Ncc69 mutants, suggesting Na⁺ recycling across the basolateral membrane. In unstimulated tubules, the principal role of the Na⁺-K⁺-ATPase is to generate a favorable electrochemical gradient for Ncc69 activity: while the Na⁺-K⁺-ATPase inhibitor ouabain decreased K⁺ flux in wild-type tubules, it had no effect in Ncc69 mutant tubules. However, in the presence of cAMP, which stimulates diuresis, additional Na⁺-K⁺-ATPase-dependent K⁺ transport pathways are recruited. In studying the effects of capa-1 on wild-type and Ncc69 mutant tubules, we found a novel antidiuretic role for this hormone that is dependent on intact Ncc69, as it was abolished in Ncc69 mutant tubules. Thus, Ncc69 plays an important role in trans-epithelial ion and fluid transport in the fly renal tubule and is a target for regulation in antidiuretic states.