Figure 4: Trafficking of K3 and K3Cys mutants.

Alexa 568-labelled native, K3 and K3Cys were introduced into mice (80 μg in 100 μl PBS; i.p.) and the retention of the labelled proteins was examined after 1 h. (a) Native Alexa 568-LCN2 was detected in kidney (proximal tubules), liver (Kupffer cells), spleen and heart, whereas K3 was nearly absent from the kidney but present in the other organs. K3Cys in contrast, was poorly visualized throughout the body. This is likely because K3Cys is rapidly and efficiently excreted. (b) Native Alexa 568-LCN2 was captured by the proximal tubule (left panel) whereas K3Cys was not visualized (middle panel). When the camera exposure time was increased (10 × ), K3Cys was found in the proximal tubule and in scattered cells in the medulla (right panel). (c) Analysis with AE1, V-ATPase and AQP2 immunocytochemistry demonstrated capture of K3Cys by principal and intercalated cells. There was limited capture of K3, and no evidence of native Alexa 568-LCN2 capture. (d) Speciation of K3Cys⁺ cells in kidney at the cortico-medullary junction. Scale bars a,b=100 μm; bars c=5 μm.