HORMONALLY CONTROLLED CHLORIDE MOVEMENT ACROSS DROSOPHILA TUBULES IS VIA ION CHANNELS IN STELLATE CELLS

Anion conductance across the Drosophila melanogaster Malpighian (renal ) tubule was investigated by a combination of physiological and transg enic techniques. Patch-clamp recordings identified clusters of 4,4'-di isothiocyanostilbene-2,2'-disulfonic acid (DIDS)-sensitive ''maxi-chlo ride'' channels in a small domain of the apical membrane. Fluid secret ion assays demonstrated sensitivity to the chloride channel blockers 5 -nitro-2-(3-phenylpropylamino)benzoic acid, diphenylamine-2-carboxylat e, anthracene-9-carboxylic acid, and niflumic acid. Electrophysiologic al analysis showed that the calcium-mediated increase in anion conduct ance was blocked by the same agents. Vibrating probe analysis revealed a small number of current density hot spots, coincident with ''stella te'' cells, that were abolished by low-chloride saline or the same chl oride channel blockers. GAL-4-targeted expression of an aequorin trans gene revealed that the neurohormone leucokinin elicits a rapid increas e in intracellular calcium levels in stellate cells that precedes the fastest demonstrable physiological effect. Taken together, these data show that leucokinins act on stellate cells through intracellular calc ium to increase transcellular chloride conductance through channels. A s electrogenic cation conductance is confined to principal cells, the two pathways are spatially segregated in this tissue.