CELL-TYPE-SPECIFIC CALCIUM SIGNALING IN A DROSOPHILA-EPITHELIUM

Calcium is a ubiquitous second messenger that plays a critical role in both excitable and non-excitable cells. Calcium mobilisation in ident ified cell types within an intact renal epithelium, the Drosophila mel anogaster Malpighian tubule, was studied by GAL4-directed expression o f an aequorin transgene, CAP(2b), a cardioactive neuropeptide that sti mulates fluid secretion by a mechanism involving nitric oxide, causes a rapid, dose-dependent rise in cytosolic calcium in only a single, ge netically-defined, set of 77 principal cells in the main (secretory) s egment of the tubule, In the absence of external calcium, the CAP(2b)- induced calcium response is abolished, In Ca2+-free medium, the endopl asmic reticulum Ca2+ ATPase inhibitor, thapsigargin, elevates [Ca2+](i ) only in the smaller stellate cells, suggesting that principal cells do not contain a thapsigargin-sensitive intracellular pool, Assays for epithelial function confirm that calcium entry is essential for CAP(2 b) to induce a physiological response in the whole organ, Furthermore, the data suggest a role for calcium signalling in the modulation of t he nitric oxide signalling pathway in this epithelium. The GAL4-target ing system allows general application to studies of cell-signalling an d pharmacology that does not rely on invasive or cytotoxic techniques.