Purpose: The inwardly rectifying potassium channel protein Kir4.1 and the water channel protein aquaporin-4 (AQP4) have been suggested to play essential roles in the potassium and water homeostasis of the retina. In this study, we investigated the expression of Kir4.1 and AQP4 in the retina during endotoxin-induced uveitis (EIU) in rats.
Methods: EIU was induced in male Wistar rats by intravitreal injection of lipopolysaccharide (LPS). The severity of the EIU was evaluated by clinical and histopathological examination. The expression of Kir4.1 and AQP4 in the retina was detected by semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR), Western blotting, and immunohistochemical staining.
Results: In the animal model of EIU, the clinical changes correlated well with the histopathological findings. The inflammation peaked at 24 h and resolved by seven day. After an intravitreal LPS injection, the expression of Kir4.1 in the retina showed a significant decline at both the protein and mRNA levels. In the early stages of EIU, the expression of Kir4.1 mRNA decreased sharply, reaching a minimum at 12 h (31%, p<0.001). It then increased gradually and had partially recovered 14 days after LPS injection (92%, p>0.05). The expression of Kir4.1 protein decreased significantly, reaching a minimum at three days after the LPS injection (43%, p<0.001). Thereafter, it increased slightly but was maintained at a low level until 14 days after LPS injection (64%, p<0.001). In contrast, the expression of AQP4 mRNA remained almost unchanged after LPS treatment (p>0.05). The expression of AQP4 protein was only slightly reduced at one day (82%, p>0.05) after LPS injection and then increased gradually and had nearly recovered to the basal level at 14 days after LPS injection.
Conclusions: EIU differently alters the expression of Kir4.1 and AQP4 in the retina. The differential expression of Kir4.1 and AQP4 during EIU implies a disturbance of water and potassium transport in the retina, which may contribute to the retinal edema during ocular inflammation.