Summary of K+ and Na+ transport across the gut and Malpighian tubules (MTs) of larval D. melanogaster. Summary of K+ and Na+ transport across the gut and Malpighian tubules (MTs) of larval D. melanogaster. The positive values represent movement of K+ or Na+ from the lumen to the haemolymph (absorption) and the negative values represent movement of K+ or Na+ from the haemolymph to the lumen (secretion). (A) K+ transport across the gut of larvae reared on the control versus the KCl-rich diet. (B) Na+ transport across the gut of larvae reared on the control versus the NaCl-rich diet. Fluxes for each segment in pmol s-1 have been calculated from scanning ion-selective electrode technique measurements (pmol cm-2 s-1) and surface areas (cm2) of each tissue segment, as described in the Materials and methods. Values are means ± s.e.m. (N=5-7 larvae). Asterisks denote significant differences (t-test, P<0.05) relative to the corresponding control. Fluxes for the main segment of the MTs were measured using the Ramsay assay (Naikkhwah and O'Donnell, 2011) and have been included for comparison. Wida Naikkhwah, and Michael J. O'Donnell J Exp Biol 2012;215:461-470 © 2012.