Regulation of the Human Epithelial Sodium Channel (ENaC) by Urokinase and Gingerol

The ENaC plays a significant role in Na+ transport through the epithelium and maintains the homeostasis of extracellular fluid volume and osmolality. Studying the proteolytic activation mechanism of the ENaC by plasmin and uPA could help improve the current understanding of the pathogenesis of salt sensitive hypertension and acute lung injury. We used oocytes from Xenopus laevis to express human ENaC and two-electrode voltage-clamp to measure the ENaC current. We found that plasmin and urokinase plasminogen activator (uPA) increase ENaC activity by 6 fold over time and the maximum activation occurred at 1 hour. To further examine the underlying mechanism, we tested several mutations of alpha and gamma ENaC in frog oocytes. Two-electrode voltage-clamp data showed that the activity of alpha422-444 truncated ENaC increased 1.3 fold with uPA treatment which was a low increase compared to the 6 fold increase we observed using uPA-treated wild type ENaC. It is possible that the 422 to 444 regions within alpha ENaC are related to the regulation of uPA on ENaC. We next treated the oocytes with gingerol, which is the major active component of fresh ginger. Gingerol immediately activated the deltabetagamma ENaC activity followed by a decrease in the channel activity within 2 min. The cRNA injected oocytes treated with gingerol had a higher death rate compared with vehicle injected oocyte.