Department of Biology, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada.
J Exp Biol. 2012 Feb 1;215(Pt 3):461-70. doi: 10.1242/jeb.064048.
Drosophila provides a useful model system for studies of the mechanisms involved in regulation of internal ion levels in response to variations in dietary salt load. This study assessed whether alterations in Na(+) and K(+) transport by the gut of larval D. melanogaster reared on salt-rich diets contribute to haemolymph ionoregulation. Na(+) and K(+) fluxes across the isolated guts of third instar larvae reared on control or salt-rich diets were measured using the scanning ion-selective electrode technique (SIET). K(+) absorption across the anterior portion of the posterior midgut of larvae reared on diet in which the concentration of KCl was increased 0.4 mol l(-1) above that in the control diet was reduced eightfold relative to the same gut segment of larvae reared on the control diet. There was also an increase in the magnitude and extent of K(+) secretion across the posterior half of the posterior midgut. Na(+) was absorbed across the ileum of larvae reared on the control diet, but was secreted across the ileum of larvae reared on diet in which the concentration of NaCl was increased 0.4 mol l(-1) above that in the control diet. There was also a small reduction in the extent of Na(+) absorption across the middle midgut of larvae reared on the NaCl-rich diet. The results indicate considerable phenotypic plasticity with respect to K(+) and Na(+) transport by the gut epithelia of larval D. melanogaster. SIET measurements of K(+) and Na(+) fluxes along the length of the gut show that ion transport mechanisms of the gut are reconfigured during salt stress so that there are reductions in K(+) and Na(+) absorption and increases in K(+) and Na(+) secretion. Together with previously described changes in salt secretion by the Malpighian tubules, these changes contribute to haemolymph ionoregulation.
果蝇为研究在盐负荷饮食变化时内部离子水平调节的机制提供了一个有用的模型系统。本研究评估了幼虫肠道中钠离子和钾离子转运的改变是否有助于血淋巴离子调节。使用扫描离子选择性电极技术（SIET）测量了在富含盐的饮食中饲养的第三龄幼虫的分离肠道中钠离子和钾离子的通量。与在对照饮食中饲养的幼虫相比，在后肠前部分中饲养的幼虫中，饮食中 KCl 浓度增加 0.4 mol l(-1)时，K(+)吸收减少了 8 倍。在后肠后半部分中也增加了 K(+)分泌的幅度和程度。在对照饮食中饲养的幼虫的回肠中吸收钠离子，但在对照饮食中 NaCl 浓度增加 0.4 mol l(-1)的饮食中饲养的幼虫的回肠中分泌钠离子。在富含 NaCl 的饮食中饲养的幼虫的中肠中，Na(+)吸收的程度也略有降低。结果表明，幼虫肠道上皮细胞的 K(+)和 Na(+)转运具有相当大的表型可塑性。SIET 测量沿肠道长度的 K(+)和 Na(+)通量表明，在盐胁迫期间，肠道的离子转运机制被重新配置，导致 K(+)和 Na(+)吸收减少，K(+)和 Na(+)分泌增加。与先前描述的马氏管盐分泌的变化一起，这些变化有助于血淋巴离子调节。
