THE IMPORTANCE OF THE GOLGI-COMPLEX FOR EPITHELIAL ION-TRANSPORT IN DROSOPHILA MALPIGHIAN TUBULES, STUDIED BY ELECTRON-MICROSCOPY, CYTOCHEMISTRY AND X-RAY-MICROANALYSIS

The distribution of potassium in the cells of Drosophila Malpighian tu bules is not homogeneous. In the microvilli of the apical part of the cell the cytoplasmic potassium content was found to be 2 to 3 times hi gher than in the neighboring intermediate cytoplasm, Data obtained by electron microscopy, histochemistry and electron probe X-ray microanal ysis indicate that glucosaminoglycans (GAGs), synthesized by the Golgi -ER complex, are responsible for potassium accumulation in the apical microvilli, Vesicles bud from the Golgi complex and then move to the a pical cell region, where they discharge their contents into the cytopl asm or into the lumen, Budded vesicles also discharge their contents i nto the hemolymph space between the folds of the basal plasma membrane . GAGs, transformed to proteoglycans (PGs), were identified on the fol ds of the basal cell surface including basal lamina by reaction with a lcian blue, Brefeldin A (BFA) was found to disintegrate Golgi-ER struc tures to vesicles, whereas budded vesicles vanished, Within the microv illi the K+-content decreased to 32%, the water content to 77%. These data provide evidence that the ER-Golgi complex is involved in the del ivery of GAGs (and PGs) into the luminal space and the hemolymph, Afte r disintegration of the Golgi complex, GAGs are missing as temporary i on stores from the vicinity of the membrane transporters.