Determining rates of epithelial solute transport by optical measurement of fluorochrome concentration gradients in the unstirred layer

We describe a method for calculating rates of fluorochrome transport from unstirred layer (USL) concentration gradients measured using confocal microscopy. Isolated Malpighian tubules or guts of Drosophila melanogaster were secured to depression slides and bathed in saline containing a fluorescent compound. By measuring the concentration gradient of fluorescent organic anions (fluorescein, Texas Red) or the P-glycoprotein substrate daunorubicin …