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 from 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.