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The Journal of Experimental Biology 204, 2289-2299 (2001)
© 2001 The Company of Biologists Limited

Analysis of epithelial K⁺ transport in Malpighian tubules of Drosophila melanogaster: evidence for spatial and temporal heterogeneity

Mark R. Rheault^* and Michael J. O’Donnell

Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4K1

*e-mail: rheaulmr{at}mcmaster.ca

Accepted April 30, 2001

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.

Key words: Drosophila melanogaster, Malpighian tubule, K⁺ transport, unstirred layer, self-referencing ion-selective microelectrode.

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