title: Analysis of epithelial K(+) transport in Malpighian tubules of Drosophila melanogaster: evidence for spatial and temporal heterogeneity.
abstract: Transport of K(+) by the lower, main and distal segments of the Malpighian tubules of Drosophila melanogaster was analyzed using self-referencing K(+)-selective microelectrodes. Transport properties of the Malpighian tubules of Drosophila melanogaster change along their length. Self-referencing ion-selective (SeRIS) microelectrode measurements (relative to the bath concentration of 20 mmoll(-1)) showed a 1% reduction (P<0.05) of [K(+)] in the unstirred layer adjacent to the main segment of the Malpighian tubules, confirming secretion of K(+) from the bath to the tubule lumen. Conversely, SeRIS measurements showed a 0.7% increase (P<0.05) in [K(+)] in the unstirred layer adjacent to the lower segment of Malpighian tubules, confirming reabsorption of K(+) from the luminal fluid to the bath. Measurements using SeRIS also showed that the distal segment neither secreted nor reabsorbed K(+). There was pronounced spatial heterogeneity in K(+) transport by the lower segment and the main segment; not all morphologically similar cells participated equally in K(+) transport, nor did all main segment cells respond equally to stimulation of K(+) transport by cyclic AMP. Pronounced temporal heterogeneity in K(+) reabsorption by the lower Malpighian tubules was also observed. We suggest that this reflects periodic reduction in K(+) reabsorption due to retention of fluid within the lower segment when the ureter contracts.
authors.affiliation: Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4K1. rheaulmr@mcmaster.ca
authors.forename: M R
authors.initials: MR
authors.lastname: Rheault
authors.forename: M J
authors.initials: MJ
authors.lastname: O'Donnell
mesh_terms: D000042:Absorption; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D000242:Cyclic AMP / Q000494:pharmacology; D006152:Cyclic GMP / Q000494:pharmacology; D004331:Drosophila melanogaster / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism; D007700:Kinetics; D008317:Malpighian Tubules / Q000378:metabolism*; D008839:Microelectrodes; D011188:Potassium / Q000378:metabolism*; D012966:Sodium Cyanide / Q000494:pharmacology
chemical_list: D000242:Cyclic AMP; D006152:Cyclic GMP; D012966:Sodium Cyanide; D011188:Potassium