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Changes in fluid secretion rate alter net transepithelial transport of MRP2 and P‐glycoprotein substrates in Malpighian tubules of Drosophila melanogaster
Author(s) -
O'Donnell Michael J.,
Leader John P.
Publication year - 2006
Publication title -
archives of insect biochemistry and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.576
H-Index - 66
eISSN - 1520-6327
pISSN - 0739-4462
DOI - 10.1002/arch.20148
Subject(s) - malpighian tubule system , secretion , multidrug resistance associated protein 2 , transepithelial potential difference , biology , medicine , endocrinology , efflux , p glycoprotein , ion transporter , chemistry , biophysics , transporter , biochemistry , atp binding cassette transporter , midgut , membrane , botany , multiple drug resistance , larva , gene , antibiotics
The effects of stimulants of fluid secretion on net transepithelial transport of the MRP2 substrate Texas Red and the p‐glycoprotein substrate daunorubicin were examined in Malpighian tubules of Drosophila melanogaster . Fluid secretion rates were determined using the Ramsay assay and secreted fluid concentrations of Texas Red and daunorubicin were determined using a microfluorometric technique. Nanoliter droplets of secreted fluid were collected in optically flat glass capillaries and dye concentration was determined from fluorescence intensity measured by confocal laser scanning microscopy. Net transepithelial flux of each compound was then calculated as the product of its concentration in the secreted fluid and the fluid secretion rate. Net transepithelial flux of Texas Red increased when fluid secretion was stimulated by tyramine, cyclic AMP or hypoosmotic saline. Net flux decreased when fluid secretion rate of cAMP‐stimulated tubules was reduced by elevating saline osmolality with sucrose. Net transepithelial flux of daunorubicin increased when fluid secretion was stimulated by cAMP. Significant increases in dye flux were seen only when the dyes were present at concentrations close to or greater than the concentration required for half maximal transport. Regression analyses showed that 57– 88% of the change in dye flux was attributable to the change in fluid secretion rate when tubules were stimulated with cAMP, cGMP, or tyramine. The results do not suggest that the effects of tyramine and cAMP are mediated through changes in transepithelial potential, nor do they indicate the direct effects of the stimulants on MRP2‐like or p‐glycoprotein‐like transporters (e.g., via protein kinases). Instead, the results suggest that increases in fluid secretion rate minimize diffusive backflux of these dyes and, thus, facilitate higher rates of net transepithelial transport indirectly. Arch. Insect Biochem. Physiol. 63:123–134, 2006. © 2006 Wiley‐Liss, Inc.