The formation of type-I concretions in Drosophila Malpighian tubules studied by electron microscopy and X-ray microanalysis

There are two types of concretions in Drosophila Malpighian tubules: Type-I concretions originate in the distal segments of the anterior tubules, type -II concretions in the adjacent transitional segment between the apical mic rovilli. Type-I concretions are formed with the aid of carbonic anhydrase w ithin intracellular vesicles, which migrate to the apical cell membrane whe re they are discharged into the lumen by exocytosis. The carbonic anhydrase inhibitors acetazolamide or hydrochlorothiazide prevent the formation of c oncretions by interruption of bicarbonate supply. In addition, the formatio n of concretions can be reduced by feeding with sodium cellulose phosphate. (C) 1998 Elsevier Science Ltd. All rights reserved.