Effects of trypsin on Na⁺ channel activity. Current–voltage relationships were generated under voltage-clamp conditions at 30-s intervals. Trypsin (3 μg/ml) was added to the bath at t = 0. Currents at −100 mV were corrected for leak current measured in the presence of 10 μM amiloride and normalized to values at t = 0. (A) Xenopus oocytes. Oocytes expressing rat αβγENaC were preincubated in low-Na solution and superfused with 110 mM Na solution. Currents were measured by two-electrode voltage clamp. Data represent means ± SEM for five oocytes. (B) Rat CCD. Whole-cell currents were measured in principal cells from the CCDs of rats maintained on a low-Na diet for 1 wk. Currents for trypsin treated (filled squares) and time controls (open squares) are plotted. Data represent means ± SEM for 13–14 cells.