Stellate cells in the Malpighian tubules of Drosophila hydei and D. melanogaster larvae (Insecta, Diptera)

The Malpighian tubules of Drosophila hydei and D. melanogaster larvae are c omposed of two types of cell, principal cells and stellate cells. In the an terior larval Malpighian tubules approximately 26% (D. hydei) and 18% (D. m elanogaster), respectively, of all cells are stellate cells. In the larvae of D. melanogaster, the stellate cells are fenestrated and the hemolymph sp ace and tubule lumen are separated only by the basal lamina. Injection of d yes into the hemolymph did not indicate any facilitated transfer of substan ces through the fenestrated cells. The principal cells of the distal segmen t are carbonic anhydrase positive indicating transport activity, whereas th e stellate cells lack this enzyme. In the stellate cells of the transitiona l segment, the sodium content is strikingly high in comparison to the neigh bouring principal cells and lumen where no sodium was detected. This findin g indicates that stellate cells reabsorb sodium as supposed earlier in 1969 by Berridge and Oschman (Tissue Cell 1:247-272).