ROMK currents along the distal nephron under control conditions. (A and B) Whole-cell currents were continuously measured at a voltage of 0 mV during addition of TPNQ (0.1 µM) and Ba²⁺ (5 mM) to the superfusate in region 1 and region 5 (see Fig. 1 A). (C) The currents through ROMK channels (I_SK) were assessed as the decrease in outward current with TPNQ and are shown as mean ± SEM for 23, 16, and 22 cells, respectively.