ENaC activity along the distal nephron under control conditions. Mice were fed a diet containing 0.5% K for 6–8 d. (A) The composite micrograph shows an isolated fragment containing two DCT segments with corresponding CNTs. The arrows indicate five regions of the fragments selected for electrophysiological analysis after being split to expose the luminal membrane. The bar graph indicates mean values of amiloride-sensitive currents in these regions in mice fed a control diet. Data represent mean ± SEM for 18, 17, 34, 29, and 17 cells, respectively, from four (DCT2, DCT2/CNT) or six (CNT, CNT/CCD) different animals. (B) ENaC currents under whole-cell voltage-clamp conditions in a cell from region 2. Currents were measured at the end of a voltage pulse of 150 ms in the presence and absence of 10 µM amiloride. The amiloride-sensitive current (I_Na) was calculated as the difference in currents at a voltage of −100 mV. (C) ENaC currents under whole-cell voltage-clamp conditions in a cell from region 4. There was no detectable response to amiloride in this cell.