Carbon dioxide causes exocytosis of vesicles containing H+ pumps in isolated perfused proximal and collecting tubules.
Carbon dioxide causes exocytosis of vesicles containing H+ pumps in isolated perfused proximal and collecting tubules.
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二氧化碳引起分离的灌注近端管和集合管中含有 H 泵的囊泡的胞吐作用。
DOI：
10.1172/jci111871
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发表时间：
1985
期刊：
影响因子：
--
通讯作者：
Al-Awqati,Q
中科院分区：
文献类型：
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作者：
Schwartz,GJ;Al-Awqati,Q
最近研究表明，在海龟膀胱中，CO2 至少部分通过引起富含 H+ 泵的囊泡与管腔质膜融合来刺激 H+ 分泌。为了测试肾脏中是否存在这种机制，我们在倒置落射荧光显微镜的载物台上用荧光素异硫氰酸酯葡聚糖（70,000 mol wt）在无CO2培养基中灌注集合管和近端直管。冲洗后，我们注意到一些集合管和所有近端直管细胞中的内吞小泡中存在点状荧光。与皮质集合管相比，外髓中更多的细胞吸收荧光右旋糖酐。利用荧光素激发光谱的 pH 依赖性，我们发现囊泡的 pH 值呈酸性（大约 pH 6）。添加质子离子载体使囊泡 pH 值增加 0.6 +/- 0.1 U，表明囊泡的酸性是由 H+ 泵引起的。添加到培养基中的 CO2（25 mmHg，pH 7.6，37°C）使皮质集合管中的荧光强度降低了 24 +/- 5%，髓质集合管中的荧光强度降低了 27 +/- 5%，近端直小管中的荧光强度降低了 25 +/- 5%。由于预先在浴液中添加秋水仙碱可以防止这种效应，因此我们认为 CO2 通过刺激囊泡的胞吐融合并从而分泌荧光右旋糖酐而导致细胞质荧光减少。当 pCO2 为 37 mmHg 的小管等水暴露于 pCO2 为 114 mmHg 时，也会发生这种胞吐融合。平均下降幅度为 53 +/- 4%。我们得出结论，集合管中的一些细胞和近端直管中的所有细胞将荧光右旋糖酐掺入顶端细胞质囊泡中，并用 H+ 泵酸化它们。 CO2 导致这些囊泡与腔膜融合，但 CO2 是否通过增加功能性 H+ 泵的数量来刺激 H+ 分泌仍有待确定。
In the turtle bladder it has recently been shown that CO2 stimulates H+ secretion, at least in part, by causing fusion of vesicles enriched in H+ pumps with the luminal plasma membrane. To test for the presence of this mechanism in the kidney we perfused collecting ducts and proximal straight tubules on the stage of an inverted epifluorescence microscope with fluorescein isothiocyanate dextran (70,000 mol wt) in CO2-free medium. After washout we noted punctate fluorescence in endocytic vesicles in some collecting ducts and in all proximal straight tubule cells. More cells took up fluorescent dextran in outer medullary than in cortical collecting ducts. Using the pH dependence of the excitation spectrum of fluorescein we found the pH of the vesicles to be acid (approximately pH 6). Addition of proton ionophores increased vesicular pH by 0.6 +/- 0.1 U, suggesting that the acidity of the vesicles was caused by H+ pumps. CO2 added to the medium (25 mmHg, pH 7.6 at 37 degrees C) reduced fluorescence intensity by 24 +/- 5% in cortical collecting ducts, 27 +/- 5% in medullary collecting ducts, and 25 +/- 5% in proximal straight tubules. Since this effect was prevented by the prior addition of colchicine to the bath, we believe that CO2 caused a decrease in cytoplasmic fluorescence by stimulating exocytotic fusion of the vesicles and thereby secretion of fluorescent dextran. This exocytotic fusion also occurred when tubules that were loaded with fluorescent dextran at a pCO2 of 37 mmHg were exposed isohydrically to a pCO2 of 114 mmHg; the mean decrease was 53 +/- 4%. We conclude that some cells in the collecting ducts and all cells in the proximal straight tubule incorporate fluorescent dextran into the apical cytoplasmic vesicles and acidify them with H+ pumps. CO2 causes fusion of these vesicles with the luminal membrane, but whether CO2 stimulates H+ secretion by increasing the number of functioning H+ pumps remains to be determined.Images