Characterization of transepithelial potential oscillations in the Drosophila Malpighian tubule.
The Malpighian tubule of Drosophila melanogaster is a useful model system for studying the regulation of epithelial ion transport. In acutely isolated tubules, the transepithelial potential (TEP) undergoes large oscillations in amplitude with a period of approximately 30s. The TEP oscillations are diminished by reductions in the peritubular chloride concentration in a manner consistent with their being caused by fluctuations in chloride conductance. The oscillations are eliminated by pretreating tubules with the calcium chelator BAPTA-AM, although removal of peritubular calcium has no effect, suggesting that the oscillations are a result of either the release of calcium from intracellular stores or the entry of calcium from the tubule lumen. Transcripts encoding two calcium-release channels, the ryanodine receptor and the inositol trisphosphate receptor, are detectable in the tubule by reverse transcription-polymerase chain reaction. To identify the cell type responsible for the oscillations, tubules were treated with diuretic hormones known to alter calcium levels in each of the two cell types. Leucokinin-IV, which increases calcium levels in the stellate cells, suppressed the oscillations, whereas cardioacceleratory peptide 2b (CAP(2b)), which increases calcium levels in the principal cells, had no effect. These data are consistent with a model in which rhythmic changes in transepithelial chloride conductance, regulated by intracellular calcium levels in the stellate cells, cause the TEP oscillations.
Blumenthal
E M
EM
Department of Biology and NSF Center for Biological Timing, PO Box 400328, University of Virginia, Charlottesville, 22904-4328, USA. eb5f@virginia.edu
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics; D002614:Chelating Agents / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism; D004331:Drosophila melanogaster / Q000502:physiology*; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004553:Electric Conductivity; D004848:Epithelium / Q000502:physiology; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008317:Malpighian Tubules / Q000737:chemistry / Q000502:physiology* / Q000648:ultrastructure; D008564:Membrane Potentials / Q000187:drug effects; D009479:Neuropeptides / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics
D015220:Calcium Channels; D002614:Chelating Agents; D002712:Chlorides; D053496:Inositol 1,4,5-Trisphosphate Receptors; D009479:Neuropeptides; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D019837:Ryanodine Receptor Calcium Release Channel; C439570:leucokinin 4; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D002118:Calcium