Alexander E A, Shih T, Schwartz J H
Renal Section, Boston Medical Center, Massachusetts, USA.
Am J Physiol. 1997 Dec;273(6):F1054-7. doi: 10.1152/ajprenal.1997.273.6.F1054.
Renal epithelial cell H+ secretion is an exocytic-endocytic phenomenon. In the inner medullary collecting duct (IMCD) cell line, which we have utilized as a model of renal epithelial cell acid secretion, we found previously that acidification increased exocytosis and alkalinization increased endocytosis. It is likely, therefore, that the rate of proton secretion is regulated by the membrane insertion and retrieval of proton pumps. There is abundant evidence from studies in the nerve terminal and the chromaffin cell that vesicle docking, membrane fusion, and discharge of vesicular contents (exocytosis) involve a series of interactions among so-called trafficking proteins. The clostridial toxins, botulinum and tetanus are proteases that specifically inactivate some of these proteins. In these experiments we demonstrated, by immunoblot and immunoprecipitation, the presence in this IMCD cell line of the specific protein targets of these toxins, synaptobrevin/vesicle-associated membrane proteins (VAMP), syntaxin, and synaptosomal-associated protein-25 (SNAP-25). Furthermore, we showed that these toxins markedly inhibit the capacity of these cells to realkalinize after an acid load. Thus these data provide new insight into the mechanism for H+ secretion in the IMCD.
肾上皮细胞氢离子分泌是一种胞吐 - 胞吞现象。在我们用作肾上皮细胞酸分泌模型的髓质内集合管（IMCD）细胞系中，我们之前发现酸化会增加胞吐作用，碱化会增加胞吞作用。因此，质子分泌速率可能受质子泵的膜插入和回收调节。来自神经末梢和嗜铬细胞研究的大量证据表明，囊泡对接、膜融合以及囊泡内容物的释放（胞吐作用）涉及一系列所谓转运蛋白之间的相互作用。肉毒杆菌毒素和破伤风毒素这两种梭菌毒素是特异性使其中一些蛋白质失活的蛋白酶。在这些实验中，我们通过免疫印迹和免疫沉淀证明，在该IMCD细胞系中存在这些毒素的特异性蛋白质靶点，即突触小泡蛋白/囊泡相关膜蛋白（VAMP）、 syntaxin和突触体相关蛋白25（SNAP - 25）。此外，我们表明这些毒素显著抑制这些细胞在酸负荷后重新碱化的能力。因此，这些数据为IMCD中氢离子分泌机制提供了新的见解。
