Wessing A, Zierold K
Institut fur Allgemeine und Spezielle Zoologie der Justus-Liebig-Universitat, Giessen, Germany.
Eur J Cell Biol. 1996 Feb;69(2):116-27.
The distribution of potassium in the cells of Drosophila Malpighian tubules 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 higher than in the neighboring intermediate cytoplasm. Data obtained by electron microscopy, histochemistry and electron probe X-ray microanalysis 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 apical cell region, where they discharge their contents into the cytoplasm or into the lumen. Budded vesicles also discharge their contents into the hemolymph space between the folds of the basal plasma membrane. GAGs, transformed to proteoglycans (PGs), were identified on the folds of the basal cell surface including basal lamina by reaction with alcian blue. Brefeldin A (BFA) was found to disintegrate Golgi-ER structures to vesicles, whereas budded vesicles vanished. Within the microvilli the K+-content decreased to 32%, the water content to 77%. These data provide evidence that the ER-Golgi complex is involved in the delivery of GAGs (and PGs) into the luminal space and the hemolymph. After disintegration of the Golgi complex, GAGs are missing as temporary ion stores from the vicinity of the membrane transporters.
果蝇马氏管细胞中钾的分布并不均匀。在细胞顶端部分的微绒毛中，发现细胞质中的钾含量比相邻的中间细胞质高2至3倍。通过电子显微镜、组织化学和电子探针X射线微分析获得的数据表明，由高尔基体-内质网复合体合成的糖胺聚糖（GAGs）负责顶端微绒毛中的钾积累。囊泡从高尔基体复合体出芽，然后移动到细胞顶端区域，在那里它们将内容物释放到细胞质或管腔中。出芽的囊泡也将其内容物释放到基底质膜褶皱之间的血淋巴空间中。通过与阿尔辛蓝反应，在包括基膜在内的基底细胞表面褶皱上鉴定出转化为蛋白聚糖（PGs）的GAGs。发现布雷菲德菌素A（BFA）会将高尔基体-内质网结构分解成囊泡，而出芽的囊泡则消失。在微绒毛内，钾含量降至32%，水分含量降至77%。这些数据证明内质网-高尔基体复合体参与了将GAGs（和PGs）输送到管腔空间和血淋巴中。高尔基体复合体解体后，GAGs作为膜转运蛋白附近的临时离子储存缺失。
