Oxidative stress-induced up-regulation of the chloride channel and Na ⁺/Ca²⁺ exchanger during cataractogenesis in diabetic rats

We have determined the abundance of the chloride channel, ClC-3, and Na⁺/Ca²⁺ exchanger proteins in isolated rat lens cortex fiber cells by immunofluorescence method using polyclonal anti-ClC-3 antibodies and monoclonal antibodies against the canine cardiac Na⁺/Ca ²⁺ exchanger protein. These proteins were also quantified in the lens cortex of streptozotocin-injected rats by Western blots. Also, mRNA for ClC-3 was determined by Northern blot analysis. The isolated rat lens cortical fibers expressed basal levels of ClC-3 and Na⁺/Ca²⁺ exchanger proteins. As compared to controls, the ClC-3 protein in the lens cortex of diabetic rats (blood glucose>400 mg%) increased by 2.5-fold in 7 days and 4.5-fold in 14 days. However, the ClC-3 protein decreased to near-normal values in 40 days. The changes in ClC-3 mRNA closely followed the protein levels. Similarly, as compared to controls, on Day 7, the Na⁺/Ca²⁺ exchanger protein in the diabetic rat lens cortex increased by 3.5-fold and on Day14 by 5.5-fold. Subsequently, it decreased to control levels on Day 40. Treatment with the antioxidant, Trolox (2 mg/kg body weight), prevented the initial increase in ClC-3 and Na⁺/Ca²⁺ exchanger proteins. The up-regulation of ClC-3 and Na⁺/Ca²⁺ exchanger proteins during the early stages of diabetes and its prevention by antioxidants suggests that the proteins regulating ion transport may have a pathophysiological role in the development of diabetic cataracts.