Figure 1.

Schematic of mechanisms of acid-base regulation of citrate transport in the proximal tubule as discussed in the text. (A) The signal transduction mechanisms addressed by Zacchia et al. (1) that act via protein trafficking between recycling endosomes (B) and the apical membrane. (C) The transported ionic species citrate⁻² increases as the pH decreases, [H⁺] increases. (D) pH also directly affects NaDC1 such that a lower pH stimulates transport. (E) Acidosis stimulates cytoplasmic and mitochondrial metabolism of citrate, promoting its reabsorption. (F) Acidosis also increases transcription of NaDC1 mRNA.