Effects of extracellular chloride ion on epithelial sodium channel (ENaC) in arginine vasotocin (AVT)-stimulated renal epithelial cells

The epithelial Na+ channel (ENaC) contributes to Control of blood pressure by reabsorbing Na+ in the cortical collecting duct of the kidney. The luminal Cl- concentration in the duct Varies Under physiological conditions. As the body Na+ content is lower, the luminal Cl concentration in the duct becomes lower. Thus, we hypothesized that the extracellular Cl- elevates ENaC activity in AVT-stimulated renal epithelial A6 cells (a model cell line of the cortical collecting duct) leading to recovery from a low body Na+ content. To clarify this point, We Studied effects of extracellular Cl- concentration on ENaC activity using cell-attached patch clamp technique. We found that ENaC had a single-channel conductance of 4.6 +/- 0.1 pS (mean +/- SE) and channel activity (open probability, Po) of 0.30 +/- 0.02 at a pipette potential of 60 mV. Lowering pipette Cl- concentration diminished Po to 0.23 +/- 0.02 associated with a significant decrease in open time front 0.78 +/- 0.03 to 0.61 +/- 0.02 s with no significant change in closed time, and shifted the current-voltage relationship leftward. These results Suggest that the extracellular Cl- regulates the ENaC-mediated Na+ reabsorption by affecting ENaC properties in AVT-stimulated renal epithelial cells.