Hormonally controlled chloride movement acrossDrosophilatubules is via ion channels in stellate cells

Abstract

Anion conductance across the Drosophila melanogaster Malpighian (renal) tubule was investigated by a combination of physiological and transgenic techniques. Patch-clamp recordings identified clusters of 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (DIDS)-sensitive “maxi-chloride” channels in a small domain of the apical membrane. Fluid secretion assays demonstrated sensitivity to the chloride channel blockers 5-nitro-2-(3-phenylpropylamino)benzoic acid, diphenylamine-2-carboxylate, anthracene-9-carboxylic acid, and niflumic acid. Electrophysiological analysis showed that the calcium-mediated increase in anion conductance was blocked by the same agents. Vibrating probe analysis revealed a small number of current density hot spots, coincident with “stellate” cells, that were abolished by low-chloride saline or the same chloride channel blockers. GAL-4-targeted expression of an aequorin transgene revealed that the neurohormone leucokinin elicits a rapid increase 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 calcium to increase transcellular chloride conductance through channels. As electrogenic cation conductance is confined to principal cells, the two pathways are spatially segregated in this tissue.

The maxi-anion channel: a classical channel playing novel roles through an unidentified molecular entity

“…These channels were similar to those observed in cultured cortical astrocytes from rats [4,49,50] and mice [5][6][7]51] as well as in a rat astrocytic RGCN cell line [52]. In epithelia, the urinary bladder [53], gastric [54], pancreatic [55][56][57], colonic [58][59][60], airway [61][62][63], choroid plexus [64], bile duct [65,66], ciliary [67][68][69], renal [9,19,[70][71][72][73][74][75][76][77][78], vestibular [79], placental [80][81][82][83][84][85][86], ruminal [87] and ovarian [84] epithelial cells were also found to express the maxianion channel with properties similar to those of excitable cells. Resembling maxi-anion channels were also found in fibroblasts [14,…”

Ecdysone signaling is required for proper organization and fluid secretion of stellate cells in the Malpighian tubules of Drosophila melanogaster

“…Malpighian tubules is an interesting tissue to study developmental biology, because firstly it does not undergo ecdysone induced degeneration (Jiang et al, 1997) and secondly it is made of cells from two different lineages (Denholm et al, 2003) which have physiologically distinct functions (Davies et al, 1996;Dow et al, 1994Dow et al, , 1998O'Donnell et al, 1996;Sozen et al, 1997;O'Donnell et al, 1998). Though ecdysone signaling in larval MTs does not lead to cell death, we find that disruption of ecdysone signaling using EcR-DN in SCs during early development results in improper morphogenesis of MTs which affects their functioning as reflected in the reduced DRIP expression.…”

“…The primary function of MTs is secretion of isotonic fluid, which is accomplished by concerted action of physiologically distinct PCs and SCs. PCs are enriched with vacuolar-H + -ATPase transporter which use Na + /H + and K + /H + exchanger to transport cations into the lumen (Davies et al, 1996;Dow et al, 1994Dow et al, , 1998O'Donnell et al, 1996;Sozen et al, 1997) while SCs express channels which permit flow of Cl -ions (O'Donnell et al, 1998) and aquaporins which permit water flow into the lumen (Dow et al, 1995;Kaufmann et al, 2005). One of the Drosophila aquaporins, Drosophila Integral Protein (DRIP), a water specific aquaporin with very high transport rate is expressed in SCs of MTs (Kaufmann et al, 2005).…”

Renal Tubule Development in Drosophila

“…Patterned cell differentiation results in the onset of the physiologic function of the tubules by the end of embryogenesis, which can be monitored by the appearance of uric acid in the lumen ( Figure 1F Figures 1G and 2F) (20). Primary urine production relies on the combined activity of the PC, which secrete K ϩ into the lumen by a vacuolar-H ϩ -ATPase transporter and K ϩ /H ϩ exchanger (21,22), and the SC, which express channels to permit the consequent flow of chloride ions and water (23,24). In insects, the activity of these transporters is hormonally regulated by diuretic peptides (for review, see reference 25).…”