Endocytic traffic is a complex and elegant operation involving cargo sorting, membrane budding and tubulation, generation of force, and the formation of organellar contacts. The role of specific proteins and lipids in these processes has been studied extensively. By comparison, precious little is understood about the contribution of the endocytic fluid to these events, despite much evidence that alteration of the contents can severely affect membrane traffic along the endocytic pathway. In particular, it has long been appreciated that dissipation of ionic gradients arrests endosome-to-lysosome maturation. How cells sense inorganic ions and transmit this information have remained largely enigmatic. Herein, we review the experimental findings that reveal an intimate association between luminal ions, their transport, and endocytic traffic. We then discuss the ionic sensors and the mechanisms proposed to convert ion concentrations into protein-based trafficking events, highlighting the current paucity of convincing explanations.

内吞交通是一种复杂而优雅的操作，涉及货物分拣、膜出芽和管状结构、力的产生以及细胞器接触的形成。已经广泛研究了特定蛋白质和脂质在这些过程中的作用。相比之下，尽管有很多证据表明内容物的改变会严重影响沿内吞途径的膜交通，但对内吞液对这些事件的贡献知之甚少。特别是，长期以来人们已经认识到离子梯度的消散会阻止内体到溶酶体的成熟。细胞如何感知无机离子并传递这些信息在很大程度上仍然是个谜。在此，我们回顾了揭示管腔离子、它们的运输和内吞运输之间的密切关联的实验结果。