The properties of the Malpighian tubules of Drosophila melanogaster change along their length. The upstream main segments secrete K(+)-rich fluid at a high rate. From this, the lower tubules reabsorb significant amounts of water and K+. Under stimulation, K+ reabsorption is accelerated. In addition, the lower tubules acidify the fluid passed to them by the main segments and secrete Ca2+ into it, adding to that transported there by the upstream epithelium. In contrast to the lumen-positive transepithelial potential difference (TEP) of the main segments, the TEP in the lower tubules is much lower and becomes lumen-negative close to their downstream junction with the common ureter. We suggest that the role of the lower tubule is to reduce the flow of K(+)-rich fluid that passes to the hindgut; this allows the hindgut to process the flow of excretory fluid more thoroughly.
Fluid reabsorption and ion transport by the lower Malpighian tubules of adult female Drosophila.
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M J O'Donnell, S H Maddrell; Fluid reabsorption and ion transport by the lower Malpighian tubules of adult female Drosophila.. J Exp Biol 1 January 1995; 198 (8): 1647–1653. doi: https://doi.org/10.1242/jeb.198.8.1647
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